linux/fs/fs-writeback.c
Linus Torvalds 8834147f95 fscache rewrite
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Merge tag 'fscache-rewrite-20220111' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

Pull fscache rewrite from David Howells:
 "This is a set of patches that rewrites the fscache driver and the
  cachefiles driver, significantly simplifying the code compared to
  what's upstream, removing the complex operation scheduling and object
  state machine in favour of something much smaller and simpler.

  The series is structured such that the first few patches disable
  fscache use by the network filesystems using it, remove the cachefiles
  driver entirely and as much of the fscache driver as can be got away
  with without causing build failures in the network filesystems.

  The patches after that recreate fscache and then cachefiles,
  attempting to add the pieces in a logical order. Finally, the
  filesystems are reenabled and then the very last patch changes the
  documentation.

  [!] Note: I have dropped the cifs patch for the moment, leaving local
      caching in cifs disabled. I've been having trouble getting that
      working. I think I have it done, but it needs more testing (there
      seem to be some test failures occurring with v5.16 also from
      xfstests), so I propose deferring that patch to the end of the
      merge window.

  WHY REWRITE?
  ============

  Fscache's operation scheduling API was intended to handle sequencing
  of cache operations, which were all required (where possible) to run
  asynchronously in parallel with the operations being done by the
  network filesystem, whilst allowing the cache to be brought online and
  offline and to interrupt service for invalidation.

  With the advent of the tmpfile capacity in the VFS, however, an
  opportunity arises to do invalidation much more simply, without having
  to wait for I/O that's actually in progress: Cachefiles can simply
  create a tmpfile, cut over the file pointer for the backing object
  attached to a cookie and abandon the in-progress I/O, dismissing it
  upon completion.

  Future work here would involve using Omar Sandoval's vfs_link() with
  AT_LINK_REPLACE[1] to allow an extant file to be displaced by a new
  hard link from a tmpfile as currently I have to unlink the old file
  first.

  These patches can also simplify the object state handling as I/O
  operations to the cache don't all have to be brought to a stop in
  order to invalidate a file. To that end, and with an eye on to writing
  a new backing cache model in the future, I've taken the opportunity to
  simplify the indexing structure.

  I've separated the index cookie concept from the file cookie concept
  by C type now. The former is now called a "volume cookie" (struct
  fscache_volume) and there is a container of file cookies. There are
  then just the two levels. All the index cookie levels are collapsed
  into a single volume cookie, and this has a single printable string as
  a key. For instance, an AFS volume would have a key of something like
  "afs,example.com,1000555", combining the filesystem name, cell name
  and volume ID. This is freeform, but must not have '/' chars in it.

  I've also eliminated all pointers back from fscache into the network
  filesystem. This required the duplication of a little bit of data in
  the cookie (cookie key, coherency data and file size), but it's not
  actually that much. This gets rid of problems with making sure we keep
  netfs data structures around so that the cache can access them.

  These patches mean that most of the code that was in the drivers
  before is simply gone and those drivers are now almost entirely new
  code. That being the case, there doesn't seem any particular reason to
  try and maintain bisectability across it. Further, there has to be a
  point in the middle where things are cut over as there's a single
  point everything has to go through (ie. /dev/cachefiles) and it can't
  be in use by two drivers at once.

  ISSUES YET OUTSTANDING
  ======================

  There are some issues still outstanding, unaddressed by this patchset,
  that will need fixing in future patchsets, but that don't stop this
  series from being usable:

  (1) The cachefiles driver needs to stop using the backing filesystem's
      metadata to store information about what parts of the cache are
      populated. This is not reliable with modern extent-based
      filesystems.

      Fixing this is deferred to a separate patchset as it involves
      negotiation with the network filesystem and the VM as to how much
      data to download to fulfil a read - which brings me on to (2)...

  (2) NFS (and CIFS with the dropped patch) do not take account of how
      the cache would like I/O to be structured to meet its granularity
      requirements. Previously, the cache used page granularity, which
      was fine as the network filesystems also dealt in page
      granularity, and the backing filesystem (ext4, xfs or whatever)
      did whatever it did out of sight. However, we now have folios to
      deal with and the cache will now have to store its own metadata to
      track its contents.

      The change I'm looking at making for cachefiles is to store
      content bitmaps in one or more xattrs and making a bit in the map
      correspond to something like a 256KiB block. However, the size of
      an xattr and the fact that they have to be read/updated in one go
      means that I'm looking at covering 1GiB of data per 512-byte map
      and storing each map in an xattr. Cachefiles has the potential to
      grow into a fully fledged filesystem of its very own if I'm not
      careful.

      However, I'm also looking at changing things even more radically
      and going to a different model of how the cache is arranged and
      managed - one that's more akin to the way, say, openafs does
      things - which brings me on to (3)...

  (3) The way cachefilesd does culling is very inefficient for large
      caches and it would be better to move it into the kernel if I can
      as cachefilesd has to keep asking the kernel if it can cull a
      file. Changing the way the backend works would allow this to be
      addressed.

  BITS THAT MAY BE CONTROVERSIAL
  ==============================

  There are some bits I've added that may be controversial:

  (1) I've provided a flag, S_KERNEL_FILE, that cachefiles uses to check
      if a files is already being used by some other kernel service
      (e.g. a duplicate cachefiles cache in the same directory) and
      reject it if it is. This isn't entirely necessary, but it helps
      prevent accidental data corruption.

      I don't want to use S_SWAPFILE as that has other effects, but
      quite possibly swapon() should set S_KERNEL_FILE too.

      Note that it doesn't prevent userspace from interfering, though
      perhaps it should. (I have made it prevent a marked directory from
      being rmdir-able).

  (2) Cachefiles wants to keep the backing file for a cookie open whilst
      we might need to write to it from network filesystem writeback.
      The problem is that the network filesystem unuses its cookie when
      its file is closed, and so we have nothing pinning the cachefiles
      file open and it will get closed automatically after a short time
      to avoid EMFILE/ENFILE problems.

      Reopening the cache file, however, is a problem if this is being
      done due to writeback triggered by exit(). Some filesystems will
      oops if we try to open a file in that context because they want to
      access current->fs or suchlike.

      To get around this, I added the following:

      (A) An inode flag, I_PINNING_FSCACHE_WB, to be set on a network
          filesystem inode to indicate that we have a usage count on the
          cookie caching that inode.

      (B) A flag in struct writeback_control, unpinned_fscache_wb, that
          is set when __writeback_single_inode() clears the last dirty
          page from i_pages - at which point it clears
          I_PINNING_FSCACHE_WB and sets this flag.

          This has to be done here so that clearing I_PINNING_FSCACHE_WB
          can be done atomically with the check of PAGECACHE_TAG_DIRTY
          that clears I_DIRTY_PAGES.

      (C) A function, fscache_set_page_dirty(), which if it is not set,
          sets I_PINNING_FSCACHE_WB and calls fscache_use_cookie() to
          pin the cache resources.

      (D) A function, fscache_unpin_writeback(), to be called by
          ->write_inode() to unuse the cookie.

      (E) A function, fscache_clear_inode_writeback(), to be called when
          the inode is evicted, before clear_inode() is called. This
          cleans up any lingering I_PINNING_FSCACHE_WB.

      The network filesystem can then use these tools to make sure that
      fscache_write_to_cache() can write locally modified data to the
      cache as well as to the server.

      For the future, I'm working on write helpers for netfs lib that
      should allow this facility to be removed by keeping track of the
      dirty regions separately - but that's incomplete at the moment and
      is also going to be affected by folios, one way or another, since
      it deals with pages"

Link: https://lore.kernel.org/all/510611.1641942444@warthog.procyon.org.uk/
Tested-by: Dominique Martinet <asmadeus@codewreck.org> # 9p
Tested-by: kafs-testing@auristor.com # afs
Tested-by: Jeff Layton <jlayton@kernel.org> # ceph
Tested-by: Dave Wysochanski <dwysocha@redhat.com> # nfs
Tested-by: Daire Byrne <daire@dneg.com> # nfs

* tag 'fscache-rewrite-20220111' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs: (67 commits)
  9p, afs, ceph, nfs: Use current_is_kswapd() rather than gfpflags_allow_blocking()
  fscache: Add a tracepoint for cookie use/unuse
  fscache: Rewrite documentation
  ceph: add fscache writeback support
  ceph: conversion to new fscache API
  nfs: Implement cache I/O by accessing the cache directly
  nfs: Convert to new fscache volume/cookie API
  9p: Copy local writes to the cache when writing to the server
  9p: Use fscache indexing rewrite and reenable caching
  afs: Skip truncation on the server of data we haven't written yet
  afs: Copy local writes to the cache when writing to the server
  afs: Convert afs to use the new fscache API
  fscache, cachefiles: Display stat of culling events
  fscache, cachefiles: Display stats of no-space events
  cachefiles: Allow cachefiles to actually function
  fscache, cachefiles: Store the volume coherency data
  cachefiles: Implement the I/O routines
  cachefiles: Implement cookie resize for truncate
  cachefiles: Implement begin and end I/O operation
  cachefiles: Implement backing file wrangling
  ...
2022-01-12 13:45:12 -08:00

2762 lines
79 KiB
C

// SPDX-License-Identifier: GPL-2.0-only
/*
* fs/fs-writeback.c
*
* Copyright (C) 2002, Linus Torvalds.
*
* Contains all the functions related to writing back and waiting
* upon dirty inodes against superblocks, and writing back dirty
* pages against inodes. ie: data writeback. Writeout of the
* inode itself is not handled here.
*
* 10Apr2002 Andrew Morton
* Split out of fs/inode.c
* Additions for address_space-based writeback
*/
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/spinlock.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/kthread.h>
#include <linux/writeback.h>
#include <linux/blkdev.h>
#include <linux/backing-dev.h>
#include <linux/tracepoint.h>
#include <linux/device.h>
#include <linux/memcontrol.h>
#include "internal.h"
/*
* 4MB minimal write chunk size
*/
#define MIN_WRITEBACK_PAGES (4096UL >> (PAGE_SHIFT - 10))
/*
* Passed into wb_writeback(), essentially a subset of writeback_control
*/
struct wb_writeback_work {
long nr_pages;
struct super_block *sb;
enum writeback_sync_modes sync_mode;
unsigned int tagged_writepages:1;
unsigned int for_kupdate:1;
unsigned int range_cyclic:1;
unsigned int for_background:1;
unsigned int for_sync:1; /* sync(2) WB_SYNC_ALL writeback */
unsigned int auto_free:1; /* free on completion */
enum wb_reason reason; /* why was writeback initiated? */
struct list_head list; /* pending work list */
struct wb_completion *done; /* set if the caller waits */
};
/*
* If an inode is constantly having its pages dirtied, but then the
* updates stop dirtytime_expire_interval seconds in the past, it's
* possible for the worst case time between when an inode has its
* timestamps updated and when they finally get written out to be two
* dirtytime_expire_intervals. We set the default to 12 hours (in
* seconds), which means most of the time inodes will have their
* timestamps written to disk after 12 hours, but in the worst case a
* few inodes might not their timestamps updated for 24 hours.
*/
unsigned int dirtytime_expire_interval = 12 * 60 * 60;
static inline struct inode *wb_inode(struct list_head *head)
{
return list_entry(head, struct inode, i_io_list);
}
/*
* Include the creation of the trace points after defining the
* wb_writeback_work structure and inline functions so that the definition
* remains local to this file.
*/
#define CREATE_TRACE_POINTS
#include <trace/events/writeback.h>
EXPORT_TRACEPOINT_SYMBOL_GPL(wbc_writepage);
static bool wb_io_lists_populated(struct bdi_writeback *wb)
{
if (wb_has_dirty_io(wb)) {
return false;
} else {
set_bit(WB_has_dirty_io, &wb->state);
WARN_ON_ONCE(!wb->avg_write_bandwidth);
atomic_long_add(wb->avg_write_bandwidth,
&wb->bdi->tot_write_bandwidth);
return true;
}
}
static void wb_io_lists_depopulated(struct bdi_writeback *wb)
{
if (wb_has_dirty_io(wb) && list_empty(&wb->b_dirty) &&
list_empty(&wb->b_io) && list_empty(&wb->b_more_io)) {
clear_bit(WB_has_dirty_io, &wb->state);
WARN_ON_ONCE(atomic_long_sub_return(wb->avg_write_bandwidth,
&wb->bdi->tot_write_bandwidth) < 0);
}
}
/**
* inode_io_list_move_locked - move an inode onto a bdi_writeback IO list
* @inode: inode to be moved
* @wb: target bdi_writeback
* @head: one of @wb->b_{dirty|io|more_io|dirty_time}
*
* Move @inode->i_io_list to @list of @wb and set %WB_has_dirty_io.
* Returns %true if @inode is the first occupant of the !dirty_time IO
* lists; otherwise, %false.
*/
static bool inode_io_list_move_locked(struct inode *inode,
struct bdi_writeback *wb,
struct list_head *head)
{
assert_spin_locked(&wb->list_lock);
list_move(&inode->i_io_list, head);
/* dirty_time doesn't count as dirty_io until expiration */
if (head != &wb->b_dirty_time)
return wb_io_lists_populated(wb);
wb_io_lists_depopulated(wb);
return false;
}
static void wb_wakeup(struct bdi_writeback *wb)
{
spin_lock_bh(&wb->work_lock);
if (test_bit(WB_registered, &wb->state))
mod_delayed_work(bdi_wq, &wb->dwork, 0);
spin_unlock_bh(&wb->work_lock);
}
static void finish_writeback_work(struct bdi_writeback *wb,
struct wb_writeback_work *work)
{
struct wb_completion *done = work->done;
if (work->auto_free)
kfree(work);
if (done) {
wait_queue_head_t *waitq = done->waitq;
/* @done can't be accessed after the following dec */
if (atomic_dec_and_test(&done->cnt))
wake_up_all(waitq);
}
}
static void wb_queue_work(struct bdi_writeback *wb,
struct wb_writeback_work *work)
{
trace_writeback_queue(wb, work);
if (work->done)
atomic_inc(&work->done->cnt);
spin_lock_bh(&wb->work_lock);
if (test_bit(WB_registered, &wb->state)) {
list_add_tail(&work->list, &wb->work_list);
mod_delayed_work(bdi_wq, &wb->dwork, 0);
} else
finish_writeback_work(wb, work);
spin_unlock_bh(&wb->work_lock);
}
/**
* wb_wait_for_completion - wait for completion of bdi_writeback_works
* @done: target wb_completion
*
* Wait for one or more work items issued to @bdi with their ->done field
* set to @done, which should have been initialized with
* DEFINE_WB_COMPLETION(). This function returns after all such work items
* are completed. Work items which are waited upon aren't freed
* automatically on completion.
*/
void wb_wait_for_completion(struct wb_completion *done)
{
atomic_dec(&done->cnt); /* put down the initial count */
wait_event(*done->waitq, !atomic_read(&done->cnt));
}
#ifdef CONFIG_CGROUP_WRITEBACK
/*
* Parameters for foreign inode detection, see wbc_detach_inode() to see
* how they're used.
*
* These paramters are inherently heuristical as the detection target
* itself is fuzzy. All we want to do is detaching an inode from the
* current owner if it's being written to by some other cgroups too much.
*
* The current cgroup writeback is built on the assumption that multiple
* cgroups writing to the same inode concurrently is very rare and a mode
* of operation which isn't well supported. As such, the goal is not
* taking too long when a different cgroup takes over an inode while
* avoiding too aggressive flip-flops from occasional foreign writes.
*
* We record, very roughly, 2s worth of IO time history and if more than
* half of that is foreign, trigger the switch. The recording is quantized
* to 16 slots. To avoid tiny writes from swinging the decision too much,
* writes smaller than 1/8 of avg size are ignored.
*/
#define WB_FRN_TIME_SHIFT 13 /* 1s = 2^13, upto 8 secs w/ 16bit */
#define WB_FRN_TIME_AVG_SHIFT 3 /* avg = avg * 7/8 + new * 1/8 */
#define WB_FRN_TIME_CUT_DIV 8 /* ignore rounds < avg / 8 */
#define WB_FRN_TIME_PERIOD (2 * (1 << WB_FRN_TIME_SHIFT)) /* 2s */
#define WB_FRN_HIST_SLOTS 16 /* inode->i_wb_frn_history is 16bit */
#define WB_FRN_HIST_UNIT (WB_FRN_TIME_PERIOD / WB_FRN_HIST_SLOTS)
/* each slot's duration is 2s / 16 */
#define WB_FRN_HIST_THR_SLOTS (WB_FRN_HIST_SLOTS / 2)
/* if foreign slots >= 8, switch */
#define WB_FRN_HIST_MAX_SLOTS (WB_FRN_HIST_THR_SLOTS / 2 + 1)
/* one round can affect upto 5 slots */
#define WB_FRN_MAX_IN_FLIGHT 1024 /* don't queue too many concurrently */
/*
* Maximum inodes per isw. A specific value has been chosen to make
* struct inode_switch_wbs_context fit into 1024 bytes kmalloc.
*/
#define WB_MAX_INODES_PER_ISW ((1024UL - sizeof(struct inode_switch_wbs_context)) \
/ sizeof(struct inode *))
static atomic_t isw_nr_in_flight = ATOMIC_INIT(0);
static struct workqueue_struct *isw_wq;
void __inode_attach_wb(struct inode *inode, struct page *page)
{
struct backing_dev_info *bdi = inode_to_bdi(inode);
struct bdi_writeback *wb = NULL;
if (inode_cgwb_enabled(inode)) {
struct cgroup_subsys_state *memcg_css;
if (page) {
memcg_css = mem_cgroup_css_from_page(page);
wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
} else {
/* must pin memcg_css, see wb_get_create() */
memcg_css = task_get_css(current, memory_cgrp_id);
wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
css_put(memcg_css);
}
}
if (!wb)
wb = &bdi->wb;
/*
* There may be multiple instances of this function racing to
* update the same inode. Use cmpxchg() to tell the winner.
*/
if (unlikely(cmpxchg(&inode->i_wb, NULL, wb)))
wb_put(wb);
}
EXPORT_SYMBOL_GPL(__inode_attach_wb);
/**
* inode_cgwb_move_to_attached - put the inode onto wb->b_attached list
* @inode: inode of interest with i_lock held
* @wb: target bdi_writeback
*
* Remove the inode from wb's io lists and if necessarily put onto b_attached
* list. Only inodes attached to cgwb's are kept on this list.
*/
static void inode_cgwb_move_to_attached(struct inode *inode,
struct bdi_writeback *wb)
{
assert_spin_locked(&wb->list_lock);
assert_spin_locked(&inode->i_lock);
inode->i_state &= ~I_SYNC_QUEUED;
if (wb != &wb->bdi->wb)
list_move(&inode->i_io_list, &wb->b_attached);
else
list_del_init(&inode->i_io_list);
wb_io_lists_depopulated(wb);
}
/**
* locked_inode_to_wb_and_lock_list - determine a locked inode's wb and lock it
* @inode: inode of interest with i_lock held
*
* Returns @inode's wb with its list_lock held. @inode->i_lock must be
* held on entry and is released on return. The returned wb is guaranteed
* to stay @inode's associated wb until its list_lock is released.
*/
static struct bdi_writeback *
locked_inode_to_wb_and_lock_list(struct inode *inode)
__releases(&inode->i_lock)
__acquires(&wb->list_lock)
{
while (true) {
struct bdi_writeback *wb = inode_to_wb(inode);
/*
* inode_to_wb() association is protected by both
* @inode->i_lock and @wb->list_lock but list_lock nests
* outside i_lock. Drop i_lock and verify that the
* association hasn't changed after acquiring list_lock.
*/
wb_get(wb);
spin_unlock(&inode->i_lock);
spin_lock(&wb->list_lock);
/* i_wb may have changed inbetween, can't use inode_to_wb() */
if (likely(wb == inode->i_wb)) {
wb_put(wb); /* @inode already has ref */
return wb;
}
spin_unlock(&wb->list_lock);
wb_put(wb);
cpu_relax();
spin_lock(&inode->i_lock);
}
}
/**
* inode_to_wb_and_lock_list - determine an inode's wb and lock it
* @inode: inode of interest
*
* Same as locked_inode_to_wb_and_lock_list() but @inode->i_lock isn't held
* on entry.
*/
static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
__acquires(&wb->list_lock)
{
spin_lock(&inode->i_lock);
return locked_inode_to_wb_and_lock_list(inode);
}
struct inode_switch_wbs_context {
struct rcu_work work;
/*
* Multiple inodes can be switched at once. The switching procedure
* consists of two parts, separated by a RCU grace period. To make
* sure that the second part is executed for each inode gone through
* the first part, all inode pointers are placed into a NULL-terminated
* array embedded into struct inode_switch_wbs_context. Otherwise
* an inode could be left in a non-consistent state.
*/
struct bdi_writeback *new_wb;
struct inode *inodes[];
};
static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi)
{
down_write(&bdi->wb_switch_rwsem);
}
static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info *bdi)
{
up_write(&bdi->wb_switch_rwsem);
}
static bool inode_do_switch_wbs(struct inode *inode,
struct bdi_writeback *old_wb,
struct bdi_writeback *new_wb)
{
struct address_space *mapping = inode->i_mapping;
XA_STATE(xas, &mapping->i_pages, 0);
struct folio *folio;
bool switched = false;
spin_lock(&inode->i_lock);
xa_lock_irq(&mapping->i_pages);
/*
* Once I_FREEING or I_WILL_FREE are visible under i_lock, the eviction
* path owns the inode and we shouldn't modify ->i_io_list.
*/
if (unlikely(inode->i_state & (I_FREEING | I_WILL_FREE)))
goto skip_switch;
trace_inode_switch_wbs(inode, old_wb, new_wb);
/*
* Count and transfer stats. Note that PAGECACHE_TAG_DIRTY points
* to possibly dirty folios while PAGECACHE_TAG_WRITEBACK points to
* folios actually under writeback.
*/
xas_for_each_marked(&xas, folio, ULONG_MAX, PAGECACHE_TAG_DIRTY) {
if (folio_test_dirty(folio)) {
long nr = folio_nr_pages(folio);
wb_stat_mod(old_wb, WB_RECLAIMABLE, -nr);
wb_stat_mod(new_wb, WB_RECLAIMABLE, nr);
}
}
xas_set(&xas, 0);
xas_for_each_marked(&xas, folio, ULONG_MAX, PAGECACHE_TAG_WRITEBACK) {
long nr = folio_nr_pages(folio);
WARN_ON_ONCE(!folio_test_writeback(folio));
wb_stat_mod(old_wb, WB_WRITEBACK, -nr);
wb_stat_mod(new_wb, WB_WRITEBACK, nr);
}
if (mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK)) {
atomic_dec(&old_wb->writeback_inodes);
atomic_inc(&new_wb->writeback_inodes);
}
wb_get(new_wb);
/*
* Transfer to @new_wb's IO list if necessary. If the @inode is dirty,
* the specific list @inode was on is ignored and the @inode is put on
* ->b_dirty which is always correct including from ->b_dirty_time.
* The transfer preserves @inode->dirtied_when ordering. If the @inode
* was clean, it means it was on the b_attached list, so move it onto
* the b_attached list of @new_wb.
*/
if (!list_empty(&inode->i_io_list)) {
inode->i_wb = new_wb;
if (inode->i_state & I_DIRTY_ALL) {
struct inode *pos;
list_for_each_entry(pos, &new_wb->b_dirty, i_io_list)
if (time_after_eq(inode->dirtied_when,
pos->dirtied_when))
break;
inode_io_list_move_locked(inode, new_wb,
pos->i_io_list.prev);
} else {
inode_cgwb_move_to_attached(inode, new_wb);
}
} else {
inode->i_wb = new_wb;
}
/* ->i_wb_frn updates may race wbc_detach_inode() but doesn't matter */
inode->i_wb_frn_winner = 0;
inode->i_wb_frn_avg_time = 0;
inode->i_wb_frn_history = 0;
switched = true;
skip_switch:
/*
* Paired with load_acquire in unlocked_inode_to_wb_begin() and
* ensures that the new wb is visible if they see !I_WB_SWITCH.
*/
smp_store_release(&inode->i_state, inode->i_state & ~I_WB_SWITCH);
xa_unlock_irq(&mapping->i_pages);
spin_unlock(&inode->i_lock);
return switched;
}
static void inode_switch_wbs_work_fn(struct work_struct *work)
{
struct inode_switch_wbs_context *isw =
container_of(to_rcu_work(work), struct inode_switch_wbs_context, work);
struct backing_dev_info *bdi = inode_to_bdi(isw->inodes[0]);
struct bdi_writeback *old_wb = isw->inodes[0]->i_wb;
struct bdi_writeback *new_wb = isw->new_wb;
unsigned long nr_switched = 0;
struct inode **inodep;
/*
* If @inode switches cgwb membership while sync_inodes_sb() is
* being issued, sync_inodes_sb() might miss it. Synchronize.
*/
down_read(&bdi->wb_switch_rwsem);
/*
* By the time control reaches here, RCU grace period has passed
* since I_WB_SWITCH assertion and all wb stat update transactions
* between unlocked_inode_to_wb_begin/end() are guaranteed to be
* synchronizing against the i_pages lock.
*
* Grabbing old_wb->list_lock, inode->i_lock and the i_pages lock
* gives us exclusion against all wb related operations on @inode
* including IO list manipulations and stat updates.
*/
if (old_wb < new_wb) {
spin_lock(&old_wb->list_lock);
spin_lock_nested(&new_wb->list_lock, SINGLE_DEPTH_NESTING);
} else {
spin_lock(&new_wb->list_lock);
spin_lock_nested(&old_wb->list_lock, SINGLE_DEPTH_NESTING);
}
for (inodep = isw->inodes; *inodep; inodep++) {
WARN_ON_ONCE((*inodep)->i_wb != old_wb);
if (inode_do_switch_wbs(*inodep, old_wb, new_wb))
nr_switched++;
}
spin_unlock(&new_wb->list_lock);
spin_unlock(&old_wb->list_lock);
up_read(&bdi->wb_switch_rwsem);
if (nr_switched) {
wb_wakeup(new_wb);
wb_put_many(old_wb, nr_switched);
}
for (inodep = isw->inodes; *inodep; inodep++)
iput(*inodep);
wb_put(new_wb);
kfree(isw);
atomic_dec(&isw_nr_in_flight);
}
static bool inode_prepare_wbs_switch(struct inode *inode,
struct bdi_writeback *new_wb)
{
/*
* Paired with smp_mb() in cgroup_writeback_umount().
* isw_nr_in_flight must be increased before checking SB_ACTIVE and
* grabbing an inode, otherwise isw_nr_in_flight can be observed as 0
* in cgroup_writeback_umount() and the isw_wq will be not flushed.
*/
smp_mb();
if (IS_DAX(inode))
return false;
/* while holding I_WB_SWITCH, no one else can update the association */
spin_lock(&inode->i_lock);
if (!(inode->i_sb->s_flags & SB_ACTIVE) ||
inode->i_state & (I_WB_SWITCH | I_FREEING | I_WILL_FREE) ||
inode_to_wb(inode) == new_wb) {
spin_unlock(&inode->i_lock);
return false;
}
inode->i_state |= I_WB_SWITCH;
__iget(inode);
spin_unlock(&inode->i_lock);
return true;
}
/**
* inode_switch_wbs - change the wb association of an inode
* @inode: target inode
* @new_wb_id: ID of the new wb
*
* Switch @inode's wb association to the wb identified by @new_wb_id. The
* switching is performed asynchronously and may fail silently.
*/
static void inode_switch_wbs(struct inode *inode, int new_wb_id)
{
struct backing_dev_info *bdi = inode_to_bdi(inode);
struct cgroup_subsys_state *memcg_css;
struct inode_switch_wbs_context *isw;
/* noop if seems to be already in progress */
if (inode->i_state & I_WB_SWITCH)
return;
/* avoid queueing a new switch if too many are already in flight */
if (atomic_read(&isw_nr_in_flight) > WB_FRN_MAX_IN_FLIGHT)
return;
isw = kzalloc(struct_size(isw, inodes, 2), GFP_ATOMIC);
if (!isw)
return;
atomic_inc(&isw_nr_in_flight);
/* find and pin the new wb */
rcu_read_lock();
memcg_css = css_from_id(new_wb_id, &memory_cgrp_subsys);
if (memcg_css && !css_tryget(memcg_css))
memcg_css = NULL;
rcu_read_unlock();
if (!memcg_css)
goto out_free;
isw->new_wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
css_put(memcg_css);
if (!isw->new_wb)
goto out_free;
if (!inode_prepare_wbs_switch(inode, isw->new_wb))
goto out_free;
isw->inodes[0] = inode;
/*
* In addition to synchronizing among switchers, I_WB_SWITCH tells
* the RCU protected stat update paths to grab the i_page
* lock so that stat transfer can synchronize against them.
* Let's continue after I_WB_SWITCH is guaranteed to be visible.
*/
INIT_RCU_WORK(&isw->work, inode_switch_wbs_work_fn);
queue_rcu_work(isw_wq, &isw->work);
return;
out_free:
atomic_dec(&isw_nr_in_flight);
if (isw->new_wb)
wb_put(isw->new_wb);
kfree(isw);
}
/**
* cleanup_offline_cgwb - detach associated inodes
* @wb: target wb
*
* Switch all inodes attached to @wb to a nearest living ancestor's wb in order
* to eventually release the dying @wb. Returns %true if not all inodes were
* switched and the function has to be restarted.
*/
bool cleanup_offline_cgwb(struct bdi_writeback *wb)
{
struct cgroup_subsys_state *memcg_css;
struct inode_switch_wbs_context *isw;
struct inode *inode;
int nr;
bool restart = false;
isw = kzalloc(struct_size(isw, inodes, WB_MAX_INODES_PER_ISW),
GFP_KERNEL);
if (!isw)
return restart;
atomic_inc(&isw_nr_in_flight);
for (memcg_css = wb->memcg_css->parent; memcg_css;
memcg_css = memcg_css->parent) {
isw->new_wb = wb_get_create(wb->bdi, memcg_css, GFP_KERNEL);
if (isw->new_wb)
break;
}
if (unlikely(!isw->new_wb))
isw->new_wb = &wb->bdi->wb; /* wb_get() is noop for bdi's wb */
nr = 0;
spin_lock(&wb->list_lock);
list_for_each_entry(inode, &wb->b_attached, i_io_list) {
if (!inode_prepare_wbs_switch(inode, isw->new_wb))
continue;
isw->inodes[nr++] = inode;
if (nr >= WB_MAX_INODES_PER_ISW - 1) {
restart = true;
break;
}
}
spin_unlock(&wb->list_lock);
/* no attached inodes? bail out */
if (nr == 0) {
atomic_dec(&isw_nr_in_flight);
wb_put(isw->new_wb);
kfree(isw);
return restart;
}
/*
* In addition to synchronizing among switchers, I_WB_SWITCH tells
* the RCU protected stat update paths to grab the i_page
* lock so that stat transfer can synchronize against them.
* Let's continue after I_WB_SWITCH is guaranteed to be visible.
*/
INIT_RCU_WORK(&isw->work, inode_switch_wbs_work_fn);
queue_rcu_work(isw_wq, &isw->work);
return restart;
}
/**
* wbc_attach_and_unlock_inode - associate wbc with target inode and unlock it
* @wbc: writeback_control of interest
* @inode: target inode
*
* @inode is locked and about to be written back under the control of @wbc.
* Record @inode's writeback context into @wbc and unlock the i_lock. On
* writeback completion, wbc_detach_inode() should be called. This is used
* to track the cgroup writeback context.
*/
void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
struct inode *inode)
{
if (!inode_cgwb_enabled(inode)) {
spin_unlock(&inode->i_lock);
return;
}
wbc->wb = inode_to_wb(inode);
wbc->inode = inode;
wbc->wb_id = wbc->wb->memcg_css->id;
wbc->wb_lcand_id = inode->i_wb_frn_winner;
wbc->wb_tcand_id = 0;
wbc->wb_bytes = 0;
wbc->wb_lcand_bytes = 0;
wbc->wb_tcand_bytes = 0;
wb_get(wbc->wb);
spin_unlock(&inode->i_lock);
/*
* A dying wb indicates that either the blkcg associated with the
* memcg changed or the associated memcg is dying. In the first
* case, a replacement wb should already be available and we should
* refresh the wb immediately. In the second case, trying to
* refresh will keep failing.
*/
if (unlikely(wb_dying(wbc->wb) && !css_is_dying(wbc->wb->memcg_css)))
inode_switch_wbs(inode, wbc->wb_id);
}
EXPORT_SYMBOL_GPL(wbc_attach_and_unlock_inode);
/**
* wbc_detach_inode - disassociate wbc from inode and perform foreign detection
* @wbc: writeback_control of the just finished writeback
*
* To be called after a writeback attempt of an inode finishes and undoes
* wbc_attach_and_unlock_inode(). Can be called under any context.
*
* As concurrent write sharing of an inode is expected to be very rare and
* memcg only tracks page ownership on first-use basis severely confining
* the usefulness of such sharing, cgroup writeback tracks ownership
* per-inode. While the support for concurrent write sharing of an inode
* is deemed unnecessary, an inode being written to by different cgroups at
* different points in time is a lot more common, and, more importantly,
* charging only by first-use can too readily lead to grossly incorrect
* behaviors (single foreign page can lead to gigabytes of writeback to be
* incorrectly attributed).
*
* To resolve this issue, cgroup writeback detects the majority dirtier of
* an inode and transfers the ownership to it. To avoid unnnecessary
* oscillation, the detection mechanism keeps track of history and gives
* out the switch verdict only if the foreign usage pattern is stable over
* a certain amount of time and/or writeback attempts.
*
* On each writeback attempt, @wbc tries to detect the majority writer
* using Boyer-Moore majority vote algorithm. In addition to the byte
* count from the majority voting, it also counts the bytes written for the
* current wb and the last round's winner wb (max of last round's current
* wb, the winner from two rounds ago, and the last round's majority
* candidate). Keeping track of the historical winner helps the algorithm
* to semi-reliably detect the most active writer even when it's not the
* absolute majority.
*
* Once the winner of the round is determined, whether the winner is
* foreign or not and how much IO time the round consumed is recorded in
* inode->i_wb_frn_history. If the amount of recorded foreign IO time is
* over a certain threshold, the switch verdict is given.
*/
void wbc_detach_inode(struct writeback_control *wbc)
{
struct bdi_writeback *wb = wbc->wb;
struct inode *inode = wbc->inode;
unsigned long avg_time, max_bytes, max_time;
u16 history;
int max_id;
if (!wb)
return;
history = inode->i_wb_frn_history;
avg_time = inode->i_wb_frn_avg_time;
/* pick the winner of this round */
if (wbc->wb_bytes >= wbc->wb_lcand_bytes &&
wbc->wb_bytes >= wbc->wb_tcand_bytes) {
max_id = wbc->wb_id;
max_bytes = wbc->wb_bytes;
} else if (wbc->wb_lcand_bytes >= wbc->wb_tcand_bytes) {
max_id = wbc->wb_lcand_id;
max_bytes = wbc->wb_lcand_bytes;
} else {
max_id = wbc->wb_tcand_id;
max_bytes = wbc->wb_tcand_bytes;
}
/*
* Calculate the amount of IO time the winner consumed and fold it
* into the running average kept per inode. If the consumed IO
* time is lower than avag / WB_FRN_TIME_CUT_DIV, ignore it for
* deciding whether to switch or not. This is to prevent one-off
* small dirtiers from skewing the verdict.
*/
max_time = DIV_ROUND_UP((max_bytes >> PAGE_SHIFT) << WB_FRN_TIME_SHIFT,
wb->avg_write_bandwidth);
if (avg_time)
avg_time += (max_time >> WB_FRN_TIME_AVG_SHIFT) -
(avg_time >> WB_FRN_TIME_AVG_SHIFT);
else
avg_time = max_time; /* immediate catch up on first run */
if (max_time >= avg_time / WB_FRN_TIME_CUT_DIV) {
int slots;
/*
* The switch verdict is reached if foreign wb's consume
* more than a certain proportion of IO time in a
* WB_FRN_TIME_PERIOD. This is loosely tracked by 16 slot
* history mask where each bit represents one sixteenth of
* the period. Determine the number of slots to shift into
* history from @max_time.
*/
slots = min(DIV_ROUND_UP(max_time, WB_FRN_HIST_UNIT),
(unsigned long)WB_FRN_HIST_MAX_SLOTS);
history <<= slots;
if (wbc->wb_id != max_id)
history |= (1U << slots) - 1;
if (history)
trace_inode_foreign_history(inode, wbc, history);
/*
* Switch if the current wb isn't the consistent winner.
* If there are multiple closely competing dirtiers, the
* inode may switch across them repeatedly over time, which
* is okay. The main goal is avoiding keeping an inode on
* the wrong wb for an extended period of time.
*/
if (hweight32(history) > WB_FRN_HIST_THR_SLOTS)
inode_switch_wbs(inode, max_id);
}
/*
* Multiple instances of this function may race to update the
* following fields but we don't mind occassional inaccuracies.
*/
inode->i_wb_frn_winner = max_id;
inode->i_wb_frn_avg_time = min(avg_time, (unsigned long)U16_MAX);
inode->i_wb_frn_history = history;
wb_put(wbc->wb);
wbc->wb = NULL;
}
EXPORT_SYMBOL_GPL(wbc_detach_inode);
/**
* wbc_account_cgroup_owner - account writeback to update inode cgroup ownership
* @wbc: writeback_control of the writeback in progress
* @page: page being written out
* @bytes: number of bytes being written out
*
* @bytes from @page are about to written out during the writeback
* controlled by @wbc. Keep the book for foreign inode detection. See
* wbc_detach_inode().
*/
void wbc_account_cgroup_owner(struct writeback_control *wbc, struct page *page,
size_t bytes)
{
struct cgroup_subsys_state *css;
int id;
/*
* pageout() path doesn't attach @wbc to the inode being written
* out. This is intentional as we don't want the function to block
* behind a slow cgroup. Ultimately, we want pageout() to kick off
* regular writeback instead of writing things out itself.
*/
if (!wbc->wb || wbc->no_cgroup_owner)
return;
css = mem_cgroup_css_from_page(page);
/* dead cgroups shouldn't contribute to inode ownership arbitration */
if (!(css->flags & CSS_ONLINE))
return;
id = css->id;
if (id == wbc->wb_id) {
wbc->wb_bytes += bytes;
return;
}
if (id == wbc->wb_lcand_id)
wbc->wb_lcand_bytes += bytes;
/* Boyer-Moore majority vote algorithm */
if (!wbc->wb_tcand_bytes)
wbc->wb_tcand_id = id;
if (id == wbc->wb_tcand_id)
wbc->wb_tcand_bytes += bytes;
else
wbc->wb_tcand_bytes -= min(bytes, wbc->wb_tcand_bytes);
}
EXPORT_SYMBOL_GPL(wbc_account_cgroup_owner);
/**
* inode_congested - test whether an inode is congested
* @inode: inode to test for congestion (may be NULL)
* @cong_bits: mask of WB_[a]sync_congested bits to test
*
* Tests whether @inode is congested. @cong_bits is the mask of congestion
* bits to test and the return value is the mask of set bits.
*
* If cgroup writeback is enabled for @inode, the congestion state is
* determined by whether the cgwb (cgroup bdi_writeback) for the blkcg
* associated with @inode is congested; otherwise, the root wb's congestion
* state is used.
*
* @inode is allowed to be NULL as this function is often called on
* mapping->host which is NULL for the swapper space.
*/
int inode_congested(struct inode *inode, int cong_bits)
{
/*
* Once set, ->i_wb never becomes NULL while the inode is alive.
* Start transaction iff ->i_wb is visible.
*/
if (inode && inode_to_wb_is_valid(inode)) {
struct bdi_writeback *wb;
struct wb_lock_cookie lock_cookie = {};
bool congested;
wb = unlocked_inode_to_wb_begin(inode, &lock_cookie);
congested = wb_congested(wb, cong_bits);
unlocked_inode_to_wb_end(inode, &lock_cookie);
return congested;
}
return wb_congested(&inode_to_bdi(inode)->wb, cong_bits);
}
EXPORT_SYMBOL_GPL(inode_congested);
/**
* wb_split_bdi_pages - split nr_pages to write according to bandwidth
* @wb: target bdi_writeback to split @nr_pages to
* @nr_pages: number of pages to write for the whole bdi
*
* Split @wb's portion of @nr_pages according to @wb's write bandwidth in
* relation to the total write bandwidth of all wb's w/ dirty inodes on
* @wb->bdi.
*/
static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
{
unsigned long this_bw = wb->avg_write_bandwidth;
unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
if (nr_pages == LONG_MAX)
return LONG_MAX;
/*
* This may be called on clean wb's and proportional distribution
* may not make sense, just use the original @nr_pages in those
* cases. In general, we wanna err on the side of writing more.
*/
if (!tot_bw || this_bw >= tot_bw)
return nr_pages;
else
return DIV_ROUND_UP_ULL((u64)nr_pages * this_bw, tot_bw);
}
/**
* bdi_split_work_to_wbs - split a wb_writeback_work to all wb's of a bdi
* @bdi: target backing_dev_info
* @base_work: wb_writeback_work to issue
* @skip_if_busy: skip wb's which already have writeback in progress
*
* Split and issue @base_work to all wb's (bdi_writeback's) of @bdi which
* have dirty inodes. If @base_work->nr_page isn't %LONG_MAX, it's
* distributed to the busy wbs according to each wb's proportion in the
* total active write bandwidth of @bdi.
*/
static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
struct wb_writeback_work *base_work,
bool skip_if_busy)
{
struct bdi_writeback *last_wb = NULL;
struct bdi_writeback *wb = list_entry(&bdi->wb_list,
struct bdi_writeback, bdi_node);
might_sleep();
restart:
rcu_read_lock();
list_for_each_entry_continue_rcu(wb, &bdi->wb_list, bdi_node) {
DEFINE_WB_COMPLETION(fallback_work_done, bdi);
struct wb_writeback_work fallback_work;
struct wb_writeback_work *work;
long nr_pages;
if (last_wb) {
wb_put(last_wb);
last_wb = NULL;
}
/* SYNC_ALL writes out I_DIRTY_TIME too */
if (!wb_has_dirty_io(wb) &&
(base_work->sync_mode == WB_SYNC_NONE ||
list_empty(&wb->b_dirty_time)))
continue;
if (skip_if_busy && writeback_in_progress(wb))
continue;
nr_pages = wb_split_bdi_pages(wb, base_work->nr_pages);
work = kmalloc(sizeof(*work), GFP_ATOMIC);
if (work) {
*work = *base_work;
work->nr_pages = nr_pages;
work->auto_free = 1;
wb_queue_work(wb, work);
continue;
}
/* alloc failed, execute synchronously using on-stack fallback */
work = &fallback_work;
*work = *base_work;
work->nr_pages = nr_pages;
work->auto_free = 0;
work->done = &fallback_work_done;
wb_queue_work(wb, work);
/*
* Pin @wb so that it stays on @bdi->wb_list. This allows
* continuing iteration from @wb after dropping and
* regrabbing rcu read lock.
*/
wb_get(wb);
last_wb = wb;
rcu_read_unlock();
wb_wait_for_completion(&fallback_work_done);
goto restart;
}
rcu_read_unlock();
if (last_wb)
wb_put(last_wb);
}
/**
* cgroup_writeback_by_id - initiate cgroup writeback from bdi and memcg IDs
* @bdi_id: target bdi id
* @memcg_id: target memcg css id
* @reason: reason why some writeback work initiated
* @done: target wb_completion
*
* Initiate flush of the bdi_writeback identified by @bdi_id and @memcg_id
* with the specified parameters.
*/
int cgroup_writeback_by_id(u64 bdi_id, int memcg_id,
enum wb_reason reason, struct wb_completion *done)
{
struct backing_dev_info *bdi;
struct cgroup_subsys_state *memcg_css;
struct bdi_writeback *wb;
struct wb_writeback_work *work;
unsigned long dirty;
int ret;
/* lookup bdi and memcg */
bdi = bdi_get_by_id(bdi_id);
if (!bdi)
return -ENOENT;
rcu_read_lock();
memcg_css = css_from_id(memcg_id, &memory_cgrp_subsys);
if (memcg_css && !css_tryget(memcg_css))
memcg_css = NULL;
rcu_read_unlock();
if (!memcg_css) {
ret = -ENOENT;
goto out_bdi_put;
}
/*
* And find the associated wb. If the wb isn't there already
* there's nothing to flush, don't create one.
*/
wb = wb_get_lookup(bdi, memcg_css);
if (!wb) {
ret = -ENOENT;
goto out_css_put;
}
/*
* The caller is attempting to write out most of
* the currently dirty pages. Let's take the current dirty page
* count and inflate it by 25% which should be large enough to
* flush out most dirty pages while avoiding getting livelocked by
* concurrent dirtiers.
*
* BTW the memcg stats are flushed periodically and this is best-effort
* estimation, so some potential error is ok.
*/
dirty = memcg_page_state(mem_cgroup_from_css(memcg_css), NR_FILE_DIRTY);
dirty = dirty * 10 / 8;
/* issue the writeback work */
work = kzalloc(sizeof(*work), GFP_NOWAIT | __GFP_NOWARN);
if (work) {
work->nr_pages = dirty;
work->sync_mode = WB_SYNC_NONE;
work->range_cyclic = 1;
work->reason = reason;
work->done = done;
work->auto_free = 1;
wb_queue_work(wb, work);
ret = 0;
} else {
ret = -ENOMEM;
}
wb_put(wb);
out_css_put:
css_put(memcg_css);
out_bdi_put:
bdi_put(bdi);
return ret;
}
/**
* cgroup_writeback_umount - flush inode wb switches for umount
*
* This function is called when a super_block is about to be destroyed and
* flushes in-flight inode wb switches. An inode wb switch goes through
* RCU and then workqueue, so the two need to be flushed in order to ensure
* that all previously scheduled switches are finished. As wb switches are
* rare occurrences and synchronize_rcu() can take a while, perform
* flushing iff wb switches are in flight.
*/
void cgroup_writeback_umount(void)
{
/*
* SB_ACTIVE should be reliably cleared before checking
* isw_nr_in_flight, see generic_shutdown_super().
*/
smp_mb();
if (atomic_read(&isw_nr_in_flight)) {
/*
* Use rcu_barrier() to wait for all pending callbacks to
* ensure that all in-flight wb switches are in the workqueue.
*/
rcu_barrier();
flush_workqueue(isw_wq);
}
}
static int __init cgroup_writeback_init(void)
{
isw_wq = alloc_workqueue("inode_switch_wbs", 0, 0);
if (!isw_wq)
return -ENOMEM;
return 0;
}
fs_initcall(cgroup_writeback_init);
#else /* CONFIG_CGROUP_WRITEBACK */
static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi) { }
static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info *bdi) { }
static void inode_cgwb_move_to_attached(struct inode *inode,
struct bdi_writeback *wb)
{
assert_spin_locked(&wb->list_lock);
assert_spin_locked(&inode->i_lock);
inode->i_state &= ~I_SYNC_QUEUED;
list_del_init(&inode->i_io_list);
wb_io_lists_depopulated(wb);
}
static struct bdi_writeback *
locked_inode_to_wb_and_lock_list(struct inode *inode)
__releases(&inode->i_lock)
__acquires(&wb->list_lock)
{
struct bdi_writeback *wb = inode_to_wb(inode);
spin_unlock(&inode->i_lock);
spin_lock(&wb->list_lock);
return wb;
}
static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
__acquires(&wb->list_lock)
{
struct bdi_writeback *wb = inode_to_wb(inode);
spin_lock(&wb->list_lock);
return wb;
}
static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
{
return nr_pages;
}
static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
struct wb_writeback_work *base_work,
bool skip_if_busy)
{
might_sleep();
if (!skip_if_busy || !writeback_in_progress(&bdi->wb)) {
base_work->auto_free = 0;
wb_queue_work(&bdi->wb, base_work);
}
}
#endif /* CONFIG_CGROUP_WRITEBACK */
/*
* Add in the number of potentially dirty inodes, because each inode
* write can dirty pagecache in the underlying blockdev.
*/
static unsigned long get_nr_dirty_pages(void)
{
return global_node_page_state(NR_FILE_DIRTY) +
get_nr_dirty_inodes();
}
static void wb_start_writeback(struct bdi_writeback *wb, enum wb_reason reason)
{
if (!wb_has_dirty_io(wb))
return;
/*
* All callers of this function want to start writeback of all
* dirty pages. Places like vmscan can call this at a very
* high frequency, causing pointless allocations of tons of
* work items and keeping the flusher threads busy retrieving
* that work. Ensure that we only allow one of them pending and
* inflight at the time.
*/
if (test_bit(WB_start_all, &wb->state) ||
test_and_set_bit(WB_start_all, &wb->state))
return;
wb->start_all_reason = reason;
wb_wakeup(wb);
}
/**
* wb_start_background_writeback - start background writeback
* @wb: bdi_writback to write from
*
* Description:
* This makes sure WB_SYNC_NONE background writeback happens. When
* this function returns, it is only guaranteed that for given wb
* some IO is happening if we are over background dirty threshold.
* Caller need not hold sb s_umount semaphore.
*/
void wb_start_background_writeback(struct bdi_writeback *wb)
{
/*
* We just wake up the flusher thread. It will perform background
* writeback as soon as there is no other work to do.
*/
trace_writeback_wake_background(wb);
wb_wakeup(wb);
}
/*
* Remove the inode from the writeback list it is on.
*/
void inode_io_list_del(struct inode *inode)
{
struct bdi_writeback *wb;
wb = inode_to_wb_and_lock_list(inode);
spin_lock(&inode->i_lock);
inode->i_state &= ~I_SYNC_QUEUED;
list_del_init(&inode->i_io_list);
wb_io_lists_depopulated(wb);
spin_unlock(&inode->i_lock);
spin_unlock(&wb->list_lock);
}
EXPORT_SYMBOL(inode_io_list_del);
/*
* mark an inode as under writeback on the sb
*/
void sb_mark_inode_writeback(struct inode *inode)
{
struct super_block *sb = inode->i_sb;
unsigned long flags;
if (list_empty(&inode->i_wb_list)) {
spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
if (list_empty(&inode->i_wb_list)) {
list_add_tail(&inode->i_wb_list, &sb->s_inodes_wb);
trace_sb_mark_inode_writeback(inode);
}
spin_unlock_irqrestore(&sb->s_inode_wblist_lock, flags);
}
}
/*
* clear an inode as under writeback on the sb
*/
void sb_clear_inode_writeback(struct inode *inode)
{
struct super_block *sb = inode->i_sb;
unsigned long flags;
if (!list_empty(&inode->i_wb_list)) {
spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
if (!list_empty(&inode->i_wb_list)) {
list_del_init(&inode->i_wb_list);
trace_sb_clear_inode_writeback(inode);
}
spin_unlock_irqrestore(&sb->s_inode_wblist_lock, flags);
}
}
/*
* Redirty an inode: set its when-it-was dirtied timestamp and move it to the
* furthest end of its superblock's dirty-inode list.
*
* Before stamping the inode's ->dirtied_when, we check to see whether it is
* already the most-recently-dirtied inode on the b_dirty list. If that is
* the case then the inode must have been redirtied while it was being written
* out and we don't reset its dirtied_when.
*/
static void redirty_tail_locked(struct inode *inode, struct bdi_writeback *wb)
{
assert_spin_locked(&inode->i_lock);
if (!list_empty(&wb->b_dirty)) {
struct inode *tail;
tail = wb_inode(wb->b_dirty.next);
if (time_before(inode->dirtied_when, tail->dirtied_when))
inode->dirtied_when = jiffies;
}
inode_io_list_move_locked(inode, wb, &wb->b_dirty);
inode->i_state &= ~I_SYNC_QUEUED;
}
static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
{
spin_lock(&inode->i_lock);
redirty_tail_locked(inode, wb);
spin_unlock(&inode->i_lock);
}
/*
* requeue inode for re-scanning after bdi->b_io list is exhausted.
*/
static void requeue_io(struct inode *inode, struct bdi_writeback *wb)
{
inode_io_list_move_locked(inode, wb, &wb->b_more_io);
}
static void inode_sync_complete(struct inode *inode)
{
inode->i_state &= ~I_SYNC;
/* If inode is clean an unused, put it into LRU now... */
inode_add_lru(inode);
/* Waiters must see I_SYNC cleared before being woken up */
smp_mb();
wake_up_bit(&inode->i_state, __I_SYNC);
}
static bool inode_dirtied_after(struct inode *inode, unsigned long t)
{
bool ret = time_after(inode->dirtied_when, t);
#ifndef CONFIG_64BIT
/*
* For inodes being constantly redirtied, dirtied_when can get stuck.
* It _appears_ to be in the future, but is actually in distant past.
* This test is necessary to prevent such wrapped-around relative times
* from permanently stopping the whole bdi writeback.
*/
ret = ret && time_before_eq(inode->dirtied_when, jiffies);
#endif
return ret;
}
#define EXPIRE_DIRTY_ATIME 0x0001
/*
* Move expired (dirtied before dirtied_before) dirty inodes from
* @delaying_queue to @dispatch_queue.
*/
static int move_expired_inodes(struct list_head *delaying_queue,
struct list_head *dispatch_queue,
unsigned long dirtied_before)
{
LIST_HEAD(tmp);
struct list_head *pos, *node;
struct super_block *sb = NULL;
struct inode *inode;
int do_sb_sort = 0;
int moved = 0;
while (!list_empty(delaying_queue)) {
inode = wb_inode(delaying_queue->prev);
if (inode_dirtied_after(inode, dirtied_before))
break;
list_move(&inode->i_io_list, &tmp);
moved++;
spin_lock(&inode->i_lock);
inode->i_state |= I_SYNC_QUEUED;
spin_unlock(&inode->i_lock);
if (sb_is_blkdev_sb(inode->i_sb))
continue;
if (sb && sb != inode->i_sb)
do_sb_sort = 1;
sb = inode->i_sb;
}
/* just one sb in list, splice to dispatch_queue and we're done */
if (!do_sb_sort) {
list_splice(&tmp, dispatch_queue);
goto out;
}
/* Move inodes from one superblock together */
while (!list_empty(&tmp)) {
sb = wb_inode(tmp.prev)->i_sb;
list_for_each_prev_safe(pos, node, &tmp) {
inode = wb_inode(pos);
if (inode->i_sb == sb)
list_move(&inode->i_io_list, dispatch_queue);
}
}
out:
return moved;
}
/*
* Queue all expired dirty inodes for io, eldest first.
* Before
* newly dirtied b_dirty b_io b_more_io
* =============> gf edc BA
* After
* newly dirtied b_dirty b_io b_more_io
* =============> g fBAedc
* |
* +--> dequeue for IO
*/
static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work,
unsigned long dirtied_before)
{
int moved;
unsigned long time_expire_jif = dirtied_before;
assert_spin_locked(&wb->list_lock);
list_splice_init(&wb->b_more_io, &wb->b_io);
moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, dirtied_before);
if (!work->for_sync)
time_expire_jif = jiffies - dirtytime_expire_interval * HZ;
moved += move_expired_inodes(&wb->b_dirty_time, &wb->b_io,
time_expire_jif);
if (moved)
wb_io_lists_populated(wb);
trace_writeback_queue_io(wb, work, dirtied_before, moved);
}
static int write_inode(struct inode *inode, struct writeback_control *wbc)
{
int ret;
if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode)) {
trace_writeback_write_inode_start(inode, wbc);
ret = inode->i_sb->s_op->write_inode(inode, wbc);
trace_writeback_write_inode(inode, wbc);
return ret;
}
return 0;
}
/*
* Wait for writeback on an inode to complete. Called with i_lock held.
* Caller must make sure inode cannot go away when we drop i_lock.
*/
static void __inode_wait_for_writeback(struct inode *inode)
__releases(inode->i_lock)
__acquires(inode->i_lock)
{
DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
wait_queue_head_t *wqh;
wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
while (inode->i_state & I_SYNC) {
spin_unlock(&inode->i_lock);
__wait_on_bit(wqh, &wq, bit_wait,
TASK_UNINTERRUPTIBLE);
spin_lock(&inode->i_lock);
}
}
/*
* Wait for writeback on an inode to complete. Caller must have inode pinned.
*/
void inode_wait_for_writeback(struct inode *inode)
{
spin_lock(&inode->i_lock);
__inode_wait_for_writeback(inode);
spin_unlock(&inode->i_lock);
}
/*
* Sleep until I_SYNC is cleared. This function must be called with i_lock
* held and drops it. It is aimed for callers not holding any inode reference
* so once i_lock is dropped, inode can go away.
*/
static void inode_sleep_on_writeback(struct inode *inode)
__releases(inode->i_lock)
{
DEFINE_WAIT(wait);
wait_queue_head_t *wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
int sleep;
prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
sleep = inode->i_state & I_SYNC;
spin_unlock(&inode->i_lock);
if (sleep)
schedule();
finish_wait(wqh, &wait);
}
/*
* Find proper writeback list for the inode depending on its current state and
* possibly also change of its state while we were doing writeback. Here we
* handle things such as livelock prevention or fairness of writeback among
* inodes. This function can be called only by flusher thread - noone else
* processes all inodes in writeback lists and requeueing inodes behind flusher
* thread's back can have unexpected consequences.
*/
static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
struct writeback_control *wbc)
{
if (inode->i_state & I_FREEING)
return;
/*
* Sync livelock prevention. Each inode is tagged and synced in one
* shot. If still dirty, it will be redirty_tail()'ed below. Update
* the dirty time to prevent enqueue and sync it again.
*/
if ((inode->i_state & I_DIRTY) &&
(wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
inode->dirtied_when = jiffies;
if (wbc->pages_skipped) {
/*
* writeback is not making progress due to locked
* buffers. Skip this inode for now.
*/
redirty_tail_locked(inode, wb);
return;
}
if (mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY)) {
/*
* We didn't write back all the pages. nfs_writepages()
* sometimes bales out without doing anything.
*/
if (wbc->nr_to_write <= 0) {
/* Slice used up. Queue for next turn. */
requeue_io(inode, wb);
} else {
/*
* Writeback blocked by something other than
* congestion. Delay the inode for some time to
* avoid spinning on the CPU (100% iowait)
* retrying writeback of the dirty page/inode
* that cannot be performed immediately.
*/
redirty_tail_locked(inode, wb);
}
} else if (inode->i_state & I_DIRTY) {
/*
* Filesystems can dirty the inode during writeback operations,
* such as delayed allocation during submission or metadata
* updates after data IO completion.
*/
redirty_tail_locked(inode, wb);
} else if (inode->i_state & I_DIRTY_TIME) {
inode->dirtied_when = jiffies;
inode_io_list_move_locked(inode, wb, &wb->b_dirty_time);
inode->i_state &= ~I_SYNC_QUEUED;
} else {
/* The inode is clean. Remove from writeback lists. */
inode_cgwb_move_to_attached(inode, wb);
}
}
/*
* Write out an inode and its dirty pages (or some of its dirty pages, depending
* on @wbc->nr_to_write), and clear the relevant dirty flags from i_state.
*
* This doesn't remove the inode from the writeback list it is on, except
* potentially to move it from b_dirty_time to b_dirty due to timestamp
* expiration. The caller is otherwise responsible for writeback list handling.
*
* The caller is also responsible for setting the I_SYNC flag beforehand and
* calling inode_sync_complete() to clear it afterwards.
*/
static int
__writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
{
struct address_space *mapping = inode->i_mapping;
long nr_to_write = wbc->nr_to_write;
unsigned dirty;
int ret;
WARN_ON(!(inode->i_state & I_SYNC));
trace_writeback_single_inode_start(inode, wbc, nr_to_write);
ret = do_writepages(mapping, wbc);
/*
* Make sure to wait on the data before writing out the metadata.
* This is important for filesystems that modify metadata on data
* I/O completion. We don't do it for sync(2) writeback because it has a
* separate, external IO completion path and ->sync_fs for guaranteeing
* inode metadata is written back correctly.
*/
if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync) {
int err = filemap_fdatawait(mapping);
if (ret == 0)
ret = err;
}
/*
* If the inode has dirty timestamps and we need to write them, call
* mark_inode_dirty_sync() to notify the filesystem about it and to
* change I_DIRTY_TIME into I_DIRTY_SYNC.
*/
if ((inode->i_state & I_DIRTY_TIME) &&
(wbc->sync_mode == WB_SYNC_ALL ||
time_after(jiffies, inode->dirtied_time_when +
dirtytime_expire_interval * HZ))) {
trace_writeback_lazytime(inode);
mark_inode_dirty_sync(inode);
}
/*
* Get and clear the dirty flags from i_state. This needs to be done
* after calling writepages because some filesystems may redirty the
* inode during writepages due to delalloc. It also needs to be done
* after handling timestamp expiration, as that may dirty the inode too.
*/
spin_lock(&inode->i_lock);
dirty = inode->i_state & I_DIRTY;
inode->i_state &= ~dirty;
/*
* Paired with smp_mb() in __mark_inode_dirty(). This allows
* __mark_inode_dirty() to test i_state without grabbing i_lock -
* either they see the I_DIRTY bits cleared or we see the dirtied
* inode.
*
* I_DIRTY_PAGES is always cleared together above even if @mapping
* still has dirty pages. The flag is reinstated after smp_mb() if
* necessary. This guarantees that either __mark_inode_dirty()
* sees clear I_DIRTY_PAGES or we see PAGECACHE_TAG_DIRTY.
*/
smp_mb();
if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
inode->i_state |= I_DIRTY_PAGES;
else if (unlikely(inode->i_state & I_PINNING_FSCACHE_WB)) {
if (!(inode->i_state & I_DIRTY_PAGES)) {
inode->i_state &= ~I_PINNING_FSCACHE_WB;
wbc->unpinned_fscache_wb = true;
dirty |= I_PINNING_FSCACHE_WB; /* Cause write_inode */
}
}
spin_unlock(&inode->i_lock);
/* Don't write the inode if only I_DIRTY_PAGES was set */
if (dirty & ~I_DIRTY_PAGES) {
int err = write_inode(inode, wbc);
if (ret == 0)
ret = err;
}
wbc->unpinned_fscache_wb = false;
trace_writeback_single_inode(inode, wbc, nr_to_write);
return ret;
}
/*
* Write out an inode's dirty data and metadata on-demand, i.e. separately from
* the regular batched writeback done by the flusher threads in
* writeback_sb_inodes(). @wbc controls various aspects of the write, such as
* whether it is a data-integrity sync (%WB_SYNC_ALL) or not (%WB_SYNC_NONE).
*
* To prevent the inode from going away, either the caller must have a reference
* to the inode, or the inode must have I_WILL_FREE or I_FREEING set.
*/
static int writeback_single_inode(struct inode *inode,
struct writeback_control *wbc)
{
struct bdi_writeback *wb;
int ret = 0;
spin_lock(&inode->i_lock);
if (!atomic_read(&inode->i_count))
WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
else
WARN_ON(inode->i_state & I_WILL_FREE);
if (inode->i_state & I_SYNC) {
/*
* Writeback is already running on the inode. For WB_SYNC_NONE,
* that's enough and we can just return. For WB_SYNC_ALL, we
* must wait for the existing writeback to complete, then do
* writeback again if there's anything left.
*/
if (wbc->sync_mode != WB_SYNC_ALL)
goto out;
__inode_wait_for_writeback(inode);
}
WARN_ON(inode->i_state & I_SYNC);
/*
* If the inode is already fully clean, then there's nothing to do.
*
* For data-integrity syncs we also need to check whether any pages are
* still under writeback, e.g. due to prior WB_SYNC_NONE writeback. If
* there are any such pages, we'll need to wait for them.
*/
if (!(inode->i_state & I_DIRTY_ALL) &&
(wbc->sync_mode != WB_SYNC_ALL ||
!mapping_tagged(inode->i_mapping, PAGECACHE_TAG_WRITEBACK)))
goto out;
inode->i_state |= I_SYNC;
wbc_attach_and_unlock_inode(wbc, inode);
ret = __writeback_single_inode(inode, wbc);
wbc_detach_inode(wbc);
wb = inode_to_wb_and_lock_list(inode);
spin_lock(&inode->i_lock);
/*
* If the inode is now fully clean, then it can be safely removed from
* its writeback list (if any). Otherwise the flusher threads are
* responsible for the writeback lists.
*/
if (!(inode->i_state & I_DIRTY_ALL))
inode_cgwb_move_to_attached(inode, wb);
spin_unlock(&wb->list_lock);
inode_sync_complete(inode);
out:
spin_unlock(&inode->i_lock);
return ret;
}
static long writeback_chunk_size(struct bdi_writeback *wb,
struct wb_writeback_work *work)
{
long pages;
/*
* WB_SYNC_ALL mode does livelock avoidance by syncing dirty
* inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
* here avoids calling into writeback_inodes_wb() more than once.
*
* The intended call sequence for WB_SYNC_ALL writeback is:
*
* wb_writeback()
* writeback_sb_inodes() <== called only once
* write_cache_pages() <== called once for each inode
* (quickly) tag currently dirty pages
* (maybe slowly) sync all tagged pages
*/
if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
pages = LONG_MAX;
else {
pages = min(wb->avg_write_bandwidth / 2,
global_wb_domain.dirty_limit / DIRTY_SCOPE);
pages = min(pages, work->nr_pages);
pages = round_down(pages + MIN_WRITEBACK_PAGES,
MIN_WRITEBACK_PAGES);
}
return pages;
}
/*
* Write a portion of b_io inodes which belong to @sb.
*
* Return the number of pages and/or inodes written.
*
* NOTE! This is called with wb->list_lock held, and will
* unlock and relock that for each inode it ends up doing
* IO for.
*/
static long writeback_sb_inodes(struct super_block *sb,
struct bdi_writeback *wb,
struct wb_writeback_work *work)
{
struct writeback_control wbc = {
.sync_mode = work->sync_mode,
.tagged_writepages = work->tagged_writepages,
.for_kupdate = work->for_kupdate,
.for_background = work->for_background,
.for_sync = work->for_sync,
.range_cyclic = work->range_cyclic,
.range_start = 0,
.range_end = LLONG_MAX,
};
unsigned long start_time = jiffies;
long write_chunk;
long wrote = 0; /* count both pages and inodes */
while (!list_empty(&wb->b_io)) {
struct inode *inode = wb_inode(wb->b_io.prev);
struct bdi_writeback *tmp_wb;
if (inode->i_sb != sb) {
if (work->sb) {
/*
* We only want to write back data for this
* superblock, move all inodes not belonging
* to it back onto the dirty list.
*/
redirty_tail(inode, wb);
continue;
}
/*
* The inode belongs to a different superblock.
* Bounce back to the caller to unpin this and
* pin the next superblock.
*/
break;
}
/*
* Don't bother with new inodes or inodes being freed, first
* kind does not need periodic writeout yet, and for the latter
* kind writeout is handled by the freer.
*/
spin_lock(&inode->i_lock);
if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
redirty_tail_locked(inode, wb);
spin_unlock(&inode->i_lock);
continue;
}
if ((inode->i_state & I_SYNC) && wbc.sync_mode != WB_SYNC_ALL) {
/*
* If this inode is locked for writeback and we are not
* doing writeback-for-data-integrity, move it to
* b_more_io so that writeback can proceed with the
* other inodes on s_io.
*
* We'll have another go at writing back this inode
* when we completed a full scan of b_io.
*/
spin_unlock(&inode->i_lock);
requeue_io(inode, wb);
trace_writeback_sb_inodes_requeue(inode);
continue;
}
spin_unlock(&wb->list_lock);
/*
* We already requeued the inode if it had I_SYNC set and we
* are doing WB_SYNC_NONE writeback. So this catches only the
* WB_SYNC_ALL case.
*/
if (inode->i_state & I_SYNC) {
/* Wait for I_SYNC. This function drops i_lock... */
inode_sleep_on_writeback(inode);
/* Inode may be gone, start again */
spin_lock(&wb->list_lock);
continue;
}
inode->i_state |= I_SYNC;
wbc_attach_and_unlock_inode(&wbc, inode);
write_chunk = writeback_chunk_size(wb, work);
wbc.nr_to_write = write_chunk;
wbc.pages_skipped = 0;
/*
* We use I_SYNC to pin the inode in memory. While it is set
* evict_inode() will wait so the inode cannot be freed.
*/
__writeback_single_inode(inode, &wbc);
wbc_detach_inode(&wbc);
work->nr_pages -= write_chunk - wbc.nr_to_write;
wrote += write_chunk - wbc.nr_to_write;
if (need_resched()) {
/*
* We're trying to balance between building up a nice
* long list of IOs to improve our merge rate, and
* getting those IOs out quickly for anyone throttling
* in balance_dirty_pages(). cond_resched() doesn't
* unplug, so get our IOs out the door before we
* give up the CPU.
*/
if (current->plug)
blk_flush_plug(current->plug, false);
cond_resched();
}
/*
* Requeue @inode if still dirty. Be careful as @inode may
* have been switched to another wb in the meantime.
*/
tmp_wb = inode_to_wb_and_lock_list(inode);
spin_lock(&inode->i_lock);
if (!(inode->i_state & I_DIRTY_ALL))
wrote++;
requeue_inode(inode, tmp_wb, &wbc);
inode_sync_complete(inode);
spin_unlock(&inode->i_lock);
if (unlikely(tmp_wb != wb)) {
spin_unlock(&tmp_wb->list_lock);
spin_lock(&wb->list_lock);
}
/*
* bail out to wb_writeback() often enough to check
* background threshold and other termination conditions.
*/
if (wrote) {
if (time_is_before_jiffies(start_time + HZ / 10UL))
break;
if (work->nr_pages <= 0)
break;
}
}
return wrote;
}
static long __writeback_inodes_wb(struct bdi_writeback *wb,
struct wb_writeback_work *work)
{
unsigned long start_time = jiffies;
long wrote = 0;
while (!list_empty(&wb->b_io)) {
struct inode *inode = wb_inode(wb->b_io.prev);
struct super_block *sb = inode->i_sb;
if (!trylock_super(sb)) {
/*
* trylock_super() may fail consistently due to
* s_umount being grabbed by someone else. Don't use
* requeue_io() to avoid busy retrying the inode/sb.
*/
redirty_tail(inode, wb);
continue;
}
wrote += writeback_sb_inodes(sb, wb, work);
up_read(&sb->s_umount);
/* refer to the same tests at the end of writeback_sb_inodes */
if (wrote) {
if (time_is_before_jiffies(start_time + HZ / 10UL))
break;
if (work->nr_pages <= 0)
break;
}
}
/* Leave any unwritten inodes on b_io */
return wrote;
}
static long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
enum wb_reason reason)
{
struct wb_writeback_work work = {
.nr_pages = nr_pages,
.sync_mode = WB_SYNC_NONE,
.range_cyclic = 1,
.reason = reason,
};
struct blk_plug plug;
blk_start_plug(&plug);
spin_lock(&wb->list_lock);
if (list_empty(&wb->b_io))
queue_io(wb, &work, jiffies);
__writeback_inodes_wb(wb, &work);
spin_unlock(&wb->list_lock);
blk_finish_plug(&plug);
return nr_pages - work.nr_pages;
}
/*
* Explicit flushing or periodic writeback of "old" data.
*
* Define "old": the first time one of an inode's pages is dirtied, we mark the
* dirtying-time in the inode's address_space. So this periodic writeback code
* just walks the superblock inode list, writing back any inodes which are
* older than a specific point in time.
*
* Try to run once per dirty_writeback_interval. But if a writeback event
* takes longer than a dirty_writeback_interval interval, then leave a
* one-second gap.
*
* dirtied_before takes precedence over nr_to_write. So we'll only write back
* all dirty pages if they are all attached to "old" mappings.
*/
static long wb_writeback(struct bdi_writeback *wb,
struct wb_writeback_work *work)
{
long nr_pages = work->nr_pages;
unsigned long dirtied_before = jiffies;
struct inode *inode;
long progress;
struct blk_plug plug;
blk_start_plug(&plug);
spin_lock(&wb->list_lock);
for (;;) {
/*
* Stop writeback when nr_pages has been consumed
*/
if (work->nr_pages <= 0)
break;
/*
* Background writeout and kupdate-style writeback may
* run forever. Stop them if there is other work to do
* so that e.g. sync can proceed. They'll be restarted
* after the other works are all done.
*/
if ((work->for_background || work->for_kupdate) &&
!list_empty(&wb->work_list))
break;
/*
* For background writeout, stop when we are below the
* background dirty threshold
*/
if (work->for_background && !wb_over_bg_thresh(wb))
break;
/*
* Kupdate and background works are special and we want to
* include all inodes that need writing. Livelock avoidance is
* handled by these works yielding to any other work so we are
* safe.
*/
if (work->for_kupdate) {
dirtied_before = jiffies -
msecs_to_jiffies(dirty_expire_interval * 10);
} else if (work->for_background)
dirtied_before = jiffies;
trace_writeback_start(wb, work);
if (list_empty(&wb->b_io))
queue_io(wb, work, dirtied_before);
if (work->sb)
progress = writeback_sb_inodes(work->sb, wb, work);
else
progress = __writeback_inodes_wb(wb, work);
trace_writeback_written(wb, work);
/*
* Did we write something? Try for more
*
* Dirty inodes are moved to b_io for writeback in batches.
* The completion of the current batch does not necessarily
* mean the overall work is done. So we keep looping as long
* as made some progress on cleaning pages or inodes.
*/
if (progress)
continue;
/*
* No more inodes for IO, bail
*/
if (list_empty(&wb->b_more_io))
break;
/*
* Nothing written. Wait for some inode to
* become available for writeback. Otherwise
* we'll just busyloop.
*/
trace_writeback_wait(wb, work);
inode = wb_inode(wb->b_more_io.prev);
spin_lock(&inode->i_lock);
spin_unlock(&wb->list_lock);
/* This function drops i_lock... */
inode_sleep_on_writeback(inode);
spin_lock(&wb->list_lock);
}
spin_unlock(&wb->list_lock);
blk_finish_plug(&plug);
return nr_pages - work->nr_pages;
}
/*
* Return the next wb_writeback_work struct that hasn't been processed yet.
*/
static struct wb_writeback_work *get_next_work_item(struct bdi_writeback *wb)
{
struct wb_writeback_work *work = NULL;
spin_lock_bh(&wb->work_lock);
if (!list_empty(&wb->work_list)) {
work = list_entry(wb->work_list.next,
struct wb_writeback_work, list);
list_del_init(&work->list);
}
spin_unlock_bh(&wb->work_lock);
return work;
}
static long wb_check_background_flush(struct bdi_writeback *wb)
{
if (wb_over_bg_thresh(wb)) {
struct wb_writeback_work work = {
.nr_pages = LONG_MAX,
.sync_mode = WB_SYNC_NONE,
.for_background = 1,
.range_cyclic = 1,
.reason = WB_REASON_BACKGROUND,
};
return wb_writeback(wb, &work);
}
return 0;
}
static long wb_check_old_data_flush(struct bdi_writeback *wb)
{
unsigned long expired;
long nr_pages;
/*
* When set to zero, disable periodic writeback
*/
if (!dirty_writeback_interval)
return 0;
expired = wb->last_old_flush +
msecs_to_jiffies(dirty_writeback_interval * 10);
if (time_before(jiffies, expired))
return 0;
wb->last_old_flush = jiffies;
nr_pages = get_nr_dirty_pages();
if (nr_pages) {
struct wb_writeback_work work = {
.nr_pages = nr_pages,
.sync_mode = WB_SYNC_NONE,
.for_kupdate = 1,
.range_cyclic = 1,
.reason = WB_REASON_PERIODIC,
};
return wb_writeback(wb, &work);
}
return 0;
}
static long wb_check_start_all(struct bdi_writeback *wb)
{
long nr_pages;
if (!test_bit(WB_start_all, &wb->state))
return 0;
nr_pages = get_nr_dirty_pages();
if (nr_pages) {
struct wb_writeback_work work = {
.nr_pages = wb_split_bdi_pages(wb, nr_pages),
.sync_mode = WB_SYNC_NONE,
.range_cyclic = 1,
.reason = wb->start_all_reason,
};
nr_pages = wb_writeback(wb, &work);
}
clear_bit(WB_start_all, &wb->state);
return nr_pages;
}
/*
* Retrieve work items and do the writeback they describe
*/
static long wb_do_writeback(struct bdi_writeback *wb)
{
struct wb_writeback_work *work;
long wrote = 0;
set_bit(WB_writeback_running, &wb->state);
while ((work = get_next_work_item(wb)) != NULL) {
trace_writeback_exec(wb, work);
wrote += wb_writeback(wb, work);
finish_writeback_work(wb, work);
}
/*
* Check for a flush-everything request
*/
wrote += wb_check_start_all(wb);
/*
* Check for periodic writeback, kupdated() style
*/
wrote += wb_check_old_data_flush(wb);
wrote += wb_check_background_flush(wb);
clear_bit(WB_writeback_running, &wb->state);
return wrote;
}
/*
* Handle writeback of dirty data for the device backed by this bdi. Also
* reschedules periodically and does kupdated style flushing.
*/
void wb_workfn(struct work_struct *work)
{
struct bdi_writeback *wb = container_of(to_delayed_work(work),
struct bdi_writeback, dwork);
long pages_written;
set_worker_desc("flush-%s", bdi_dev_name(wb->bdi));
current->flags |= PF_SWAPWRITE;
if (likely(!current_is_workqueue_rescuer() ||
!test_bit(WB_registered, &wb->state))) {
/*
* The normal path. Keep writing back @wb until its
* work_list is empty. Note that this path is also taken
* if @wb is shutting down even when we're running off the
* rescuer as work_list needs to be drained.
*/
do {
pages_written = wb_do_writeback(wb);
trace_writeback_pages_written(pages_written);
} while (!list_empty(&wb->work_list));
} else {
/*
* bdi_wq can't get enough workers and we're running off
* the emergency worker. Don't hog it. Hopefully, 1024 is
* enough for efficient IO.
*/
pages_written = writeback_inodes_wb(wb, 1024,
WB_REASON_FORKER_THREAD);
trace_writeback_pages_written(pages_written);
}
if (!list_empty(&wb->work_list))
wb_wakeup(wb);
else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
wb_wakeup_delayed(wb);
current->flags &= ~PF_SWAPWRITE;
}
/*
* Start writeback of `nr_pages' pages on this bdi. If `nr_pages' is zero,
* write back the whole world.
*/
static void __wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
enum wb_reason reason)
{
struct bdi_writeback *wb;
if (!bdi_has_dirty_io(bdi))
return;
list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
wb_start_writeback(wb, reason);
}
void wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
enum wb_reason reason)
{
rcu_read_lock();
__wakeup_flusher_threads_bdi(bdi, reason);
rcu_read_unlock();
}
/*
* Wakeup the flusher threads to start writeback of all currently dirty pages
*/
void wakeup_flusher_threads(enum wb_reason reason)
{
struct backing_dev_info *bdi;
/*
* If we are expecting writeback progress we must submit plugged IO.
*/
if (blk_needs_flush_plug(current))
blk_flush_plug(current->plug, true);
rcu_read_lock();
list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
__wakeup_flusher_threads_bdi(bdi, reason);
rcu_read_unlock();
}
/*
* Wake up bdi's periodically to make sure dirtytime inodes gets
* written back periodically. We deliberately do *not* check the
* b_dirtytime list in wb_has_dirty_io(), since this would cause the
* kernel to be constantly waking up once there are any dirtytime
* inodes on the system. So instead we define a separate delayed work
* function which gets called much more rarely. (By default, only
* once every 12 hours.)
*
* If there is any other write activity going on in the file system,
* this function won't be necessary. But if the only thing that has
* happened on the file system is a dirtytime inode caused by an atime
* update, we need this infrastructure below to make sure that inode
* eventually gets pushed out to disk.
*/
static void wakeup_dirtytime_writeback(struct work_struct *w);
static DECLARE_DELAYED_WORK(dirtytime_work, wakeup_dirtytime_writeback);
static void wakeup_dirtytime_writeback(struct work_struct *w)
{
struct backing_dev_info *bdi;
rcu_read_lock();
list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
struct bdi_writeback *wb;
list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
if (!list_empty(&wb->b_dirty_time))
wb_wakeup(wb);
}
rcu_read_unlock();
schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
}
static int __init start_dirtytime_writeback(void)
{
schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
return 0;
}
__initcall(start_dirtytime_writeback);
int dirtytime_interval_handler(struct ctl_table *table, int write,
void *buffer, size_t *lenp, loff_t *ppos)
{
int ret;
ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
if (ret == 0 && write)
mod_delayed_work(system_wq, &dirtytime_work, 0);
return ret;
}
/**
* __mark_inode_dirty - internal function to mark an inode dirty
*
* @inode: inode to mark
* @flags: what kind of dirty, e.g. I_DIRTY_SYNC. This can be a combination of
* multiple I_DIRTY_* flags, except that I_DIRTY_TIME can't be combined
* with I_DIRTY_PAGES.
*
* Mark an inode as dirty. We notify the filesystem, then update the inode's
* dirty flags. Then, if needed we add the inode to the appropriate dirty list.
*
* Most callers should use mark_inode_dirty() or mark_inode_dirty_sync()
* instead of calling this directly.
*
* CAREFUL! We only add the inode to the dirty list if it is hashed or if it
* refers to a blockdev. Unhashed inodes will never be added to the dirty list
* even if they are later hashed, as they will have been marked dirty already.
*
* In short, ensure you hash any inodes _before_ you start marking them dirty.
*
* Note that for blockdevs, inode->dirtied_when represents the dirtying time of
* the block-special inode (/dev/hda1) itself. And the ->dirtied_when field of
* the kernel-internal blockdev inode represents the dirtying time of the
* blockdev's pages. This is why for I_DIRTY_PAGES we always use
* page->mapping->host, so the page-dirtying time is recorded in the internal
* blockdev inode.
*/
void __mark_inode_dirty(struct inode *inode, int flags)
{
struct super_block *sb = inode->i_sb;
int dirtytime = 0;
trace_writeback_mark_inode_dirty(inode, flags);
if (flags & I_DIRTY_INODE) {
/*
* Notify the filesystem about the inode being dirtied, so that
* (if needed) it can update on-disk fields and journal the
* inode. This is only needed when the inode itself is being
* dirtied now. I.e. it's only needed for I_DIRTY_INODE, not
* for just I_DIRTY_PAGES or I_DIRTY_TIME.
*/
trace_writeback_dirty_inode_start(inode, flags);
if (sb->s_op->dirty_inode)
sb->s_op->dirty_inode(inode, flags & I_DIRTY_INODE);
trace_writeback_dirty_inode(inode, flags);
/* I_DIRTY_INODE supersedes I_DIRTY_TIME. */
flags &= ~I_DIRTY_TIME;
} else {
/*
* Else it's either I_DIRTY_PAGES, I_DIRTY_TIME, or nothing.
* (We don't support setting both I_DIRTY_PAGES and I_DIRTY_TIME
* in one call to __mark_inode_dirty().)
*/
dirtytime = flags & I_DIRTY_TIME;
WARN_ON_ONCE(dirtytime && flags != I_DIRTY_TIME);
}
/*
* Paired with smp_mb() in __writeback_single_inode() for the
* following lockless i_state test. See there for details.
*/
smp_mb();
if (((inode->i_state & flags) == flags) ||
(dirtytime && (inode->i_state & I_DIRTY_INODE)))
return;
spin_lock(&inode->i_lock);
if (dirtytime && (inode->i_state & I_DIRTY_INODE))
goto out_unlock_inode;
if ((inode->i_state & flags) != flags) {
const int was_dirty = inode->i_state & I_DIRTY;
inode_attach_wb(inode, NULL);
/* I_DIRTY_INODE supersedes I_DIRTY_TIME. */
if (flags & I_DIRTY_INODE)
inode->i_state &= ~I_DIRTY_TIME;
inode->i_state |= flags;
/*
* If the inode is queued for writeback by flush worker, just
* update its dirty state. Once the flush worker is done with
* the inode it will place it on the appropriate superblock
* list, based upon its state.
*/
if (inode->i_state & I_SYNC_QUEUED)
goto out_unlock_inode;
/*
* Only add valid (hashed) inodes to the superblock's
* dirty list. Add blockdev inodes as well.
*/
if (!S_ISBLK(inode->i_mode)) {
if (inode_unhashed(inode))
goto out_unlock_inode;
}
if (inode->i_state & I_FREEING)
goto out_unlock_inode;
/*
* If the inode was already on b_dirty/b_io/b_more_io, don't
* reposition it (that would break b_dirty time-ordering).
*/
if (!was_dirty) {
struct bdi_writeback *wb;
struct list_head *dirty_list;
bool wakeup_bdi = false;
wb = locked_inode_to_wb_and_lock_list(inode);
inode->dirtied_when = jiffies;
if (dirtytime)
inode->dirtied_time_when = jiffies;
if (inode->i_state & I_DIRTY)
dirty_list = &wb->b_dirty;
else
dirty_list = &wb->b_dirty_time;
wakeup_bdi = inode_io_list_move_locked(inode, wb,
dirty_list);
spin_unlock(&wb->list_lock);
trace_writeback_dirty_inode_enqueue(inode);
/*
* If this is the first dirty inode for this bdi,
* we have to wake-up the corresponding bdi thread
* to make sure background write-back happens
* later.
*/
if (wakeup_bdi &&
(wb->bdi->capabilities & BDI_CAP_WRITEBACK))
wb_wakeup_delayed(wb);
return;
}
}
out_unlock_inode:
spin_unlock(&inode->i_lock);
}
EXPORT_SYMBOL(__mark_inode_dirty);
/*
* The @s_sync_lock is used to serialise concurrent sync operations
* to avoid lock contention problems with concurrent wait_sb_inodes() calls.
* Concurrent callers will block on the s_sync_lock rather than doing contending
* walks. The queueing maintains sync(2) required behaviour as all the IO that
* has been issued up to the time this function is enter is guaranteed to be
* completed by the time we have gained the lock and waited for all IO that is
* in progress regardless of the order callers are granted the lock.
*/
static void wait_sb_inodes(struct super_block *sb)
{
LIST_HEAD(sync_list);
/*
* We need to be protected against the filesystem going from
* r/o to r/w or vice versa.
*/
WARN_ON(!rwsem_is_locked(&sb->s_umount));
mutex_lock(&sb->s_sync_lock);
/*
* Splice the writeback list onto a temporary list to avoid waiting on
* inodes that have started writeback after this point.
*
* Use rcu_read_lock() to keep the inodes around until we have a
* reference. s_inode_wblist_lock protects sb->s_inodes_wb as well as
* the local list because inodes can be dropped from either by writeback
* completion.
*/
rcu_read_lock();
spin_lock_irq(&sb->s_inode_wblist_lock);
list_splice_init(&sb->s_inodes_wb, &sync_list);
/*
* Data integrity sync. Must wait for all pages under writeback, because
* there may have been pages dirtied before our sync call, but which had
* writeout started before we write it out. In which case, the inode
* may not be on the dirty list, but we still have to wait for that
* writeout.
*/
while (!list_empty(&sync_list)) {
struct inode *inode = list_first_entry(&sync_list, struct inode,
i_wb_list);
struct address_space *mapping = inode->i_mapping;
/*
* Move each inode back to the wb list before we drop the lock
* to preserve consistency between i_wb_list and the mapping
* writeback tag. Writeback completion is responsible to remove
* the inode from either list once the writeback tag is cleared.
*/
list_move_tail(&inode->i_wb_list, &sb->s_inodes_wb);
/*
* The mapping can appear untagged while still on-list since we
* do not have the mapping lock. Skip it here, wb completion
* will remove it.
*/
if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
continue;
spin_unlock_irq(&sb->s_inode_wblist_lock);
spin_lock(&inode->i_lock);
if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) {
spin_unlock(&inode->i_lock);
spin_lock_irq(&sb->s_inode_wblist_lock);
continue;
}
__iget(inode);
spin_unlock(&inode->i_lock);
rcu_read_unlock();
/*
* We keep the error status of individual mapping so that
* applications can catch the writeback error using fsync(2).
* See filemap_fdatawait_keep_errors() for details.
*/
filemap_fdatawait_keep_errors(mapping);
cond_resched();
iput(inode);
rcu_read_lock();
spin_lock_irq(&sb->s_inode_wblist_lock);
}
spin_unlock_irq(&sb->s_inode_wblist_lock);
rcu_read_unlock();
mutex_unlock(&sb->s_sync_lock);
}
static void __writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,
enum wb_reason reason, bool skip_if_busy)
{
struct backing_dev_info *bdi = sb->s_bdi;
DEFINE_WB_COMPLETION(done, bdi);
struct wb_writeback_work work = {
.sb = sb,
.sync_mode = WB_SYNC_NONE,
.tagged_writepages = 1,
.done = &done,
.nr_pages = nr,
.reason = reason,
};
if (!bdi_has_dirty_io(bdi) || bdi == &noop_backing_dev_info)
return;
WARN_ON(!rwsem_is_locked(&sb->s_umount));
bdi_split_work_to_wbs(sb->s_bdi, &work, skip_if_busy);
wb_wait_for_completion(&done);
}
/**
* writeback_inodes_sb_nr - writeback dirty inodes from given super_block
* @sb: the superblock
* @nr: the number of pages to write
* @reason: reason why some writeback work initiated
*
* Start writeback on some inodes on this super_block. No guarantees are made
* on how many (if any) will be written, and this function does not wait
* for IO completion of submitted IO.
*/
void writeback_inodes_sb_nr(struct super_block *sb,
unsigned long nr,
enum wb_reason reason)
{
__writeback_inodes_sb_nr(sb, nr, reason, false);
}
EXPORT_SYMBOL(writeback_inodes_sb_nr);
/**
* writeback_inodes_sb - writeback dirty inodes from given super_block
* @sb: the superblock
* @reason: reason why some writeback work was initiated
*
* Start writeback on some inodes on this super_block. No guarantees are made
* on how many (if any) will be written, and this function does not wait
* for IO completion of submitted IO.
*/
void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
{
return writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
}
EXPORT_SYMBOL(writeback_inodes_sb);
/**
* try_to_writeback_inodes_sb - try to start writeback if none underway
* @sb: the superblock
* @reason: reason why some writeback work was initiated
*
* Invoke __writeback_inodes_sb_nr if no writeback is currently underway.
*/
void try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
{
if (!down_read_trylock(&sb->s_umount))
return;
__writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason, true);
up_read(&sb->s_umount);
}
EXPORT_SYMBOL(try_to_writeback_inodes_sb);
/**
* sync_inodes_sb - sync sb inode pages
* @sb: the superblock
*
* This function writes and waits on any dirty inode belonging to this
* super_block.
*/
void sync_inodes_sb(struct super_block *sb)
{
struct backing_dev_info *bdi = sb->s_bdi;
DEFINE_WB_COMPLETION(done, bdi);
struct wb_writeback_work work = {
.sb = sb,
.sync_mode = WB_SYNC_ALL,
.nr_pages = LONG_MAX,
.range_cyclic = 0,
.done = &done,
.reason = WB_REASON_SYNC,
.for_sync = 1,
};
/*
* Can't skip on !bdi_has_dirty() because we should wait for !dirty
* inodes under writeback and I_DIRTY_TIME inodes ignored by
* bdi_has_dirty() need to be written out too.
*/
if (bdi == &noop_backing_dev_info)
return;
WARN_ON(!rwsem_is_locked(&sb->s_umount));
/* protect against inode wb switch, see inode_switch_wbs_work_fn() */
bdi_down_write_wb_switch_rwsem(bdi);
bdi_split_work_to_wbs(bdi, &work, false);
wb_wait_for_completion(&done);
bdi_up_write_wb_switch_rwsem(bdi);
wait_sb_inodes(sb);
}
EXPORT_SYMBOL(sync_inodes_sb);
/**
* write_inode_now - write an inode to disk
* @inode: inode to write to disk
* @sync: whether the write should be synchronous or not
*
* This function commits an inode to disk immediately if it is dirty. This is
* primarily needed by knfsd.
*
* The caller must either have a ref on the inode or must have set I_WILL_FREE.
*/
int write_inode_now(struct inode *inode, int sync)
{
struct writeback_control wbc = {
.nr_to_write = LONG_MAX,
.sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
.range_start = 0,
.range_end = LLONG_MAX,
};
if (!mapping_can_writeback(inode->i_mapping))
wbc.nr_to_write = 0;
might_sleep();
return writeback_single_inode(inode, &wbc);
}
EXPORT_SYMBOL(write_inode_now);
/**
* sync_inode_metadata - write an inode to disk
* @inode: the inode to sync
* @wait: wait for I/O to complete.
*
* Write an inode to disk and adjust its dirty state after completion.
*
* Note: only writes the actual inode, no associated data or other metadata.
*/
int sync_inode_metadata(struct inode *inode, int wait)
{
struct writeback_control wbc = {
.sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
.nr_to_write = 0, /* metadata-only */
};
return writeback_single_inode(inode, &wbc);
}
EXPORT_SYMBOL(sync_inode_metadata);