linux/fs/fscache/cache.c
David Howells 402cb8dda9 fscache: Attach the index key and aux data to the cookie
Attach copies of the index key and auxiliary data to the fscache cookie so
that:

 (1) The callbacks to the netfs for this stuff can be eliminated.  This
     can simplify things in the cache as the information is still
     available, even after the cache has relinquished the cookie.

 (2) Simplifies the locking requirements of accessing the information as we
     don't have to worry about the netfs object going away on us.

 (3) The cache can do lazy updating of the coherency information on disk.
     As long as the cache is flushed before reboot/poweroff, there's no
     need to update the coherency info on disk every time it changes.

 (4) Cookies can be hashed or put in a tree as the index key is easily
     available.  This allows:

     (a) Checks for duplicate cookies can be made at the top fscache layer
     	 rather than down in the bowels of the cache backend.

     (b) Caching can be added to a netfs object that has a cookie if the
     	 cache is brought online after the netfs object is allocated.

A certain amount of space is made in the cookie for inline copies of the
data, but if it won't fit there, extra memory will be allocated for it.

The downside of this is that live cache operation requires more memory.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Anna Schumaker <anna.schumaker@netapp.com>
Tested-by: Steve Dickson <steved@redhat.com>
2018-04-04 13:41:28 +01:00

422 lines
11 KiB
C

/* FS-Cache cache handling
*
* Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
#define FSCACHE_DEBUG_LEVEL CACHE
#include <linux/module.h>
#include <linux/slab.h>
#include "internal.h"
LIST_HEAD(fscache_cache_list);
DECLARE_RWSEM(fscache_addremove_sem);
DECLARE_WAIT_QUEUE_HEAD(fscache_cache_cleared_wq);
EXPORT_SYMBOL(fscache_cache_cleared_wq);
static LIST_HEAD(fscache_cache_tag_list);
/*
* look up a cache tag
*/
struct fscache_cache_tag *__fscache_lookup_cache_tag(const char *name)
{
struct fscache_cache_tag *tag, *xtag;
/* firstly check for the existence of the tag under read lock */
down_read(&fscache_addremove_sem);
list_for_each_entry(tag, &fscache_cache_tag_list, link) {
if (strcmp(tag->name, name) == 0) {
atomic_inc(&tag->usage);
up_read(&fscache_addremove_sem);
return tag;
}
}
up_read(&fscache_addremove_sem);
/* the tag does not exist - create a candidate */
xtag = kzalloc(sizeof(*xtag) + strlen(name) + 1, GFP_KERNEL);
if (!xtag)
/* return a dummy tag if out of memory */
return ERR_PTR(-ENOMEM);
atomic_set(&xtag->usage, 1);
strcpy(xtag->name, name);
/* write lock, search again and add if still not present */
down_write(&fscache_addremove_sem);
list_for_each_entry(tag, &fscache_cache_tag_list, link) {
if (strcmp(tag->name, name) == 0) {
atomic_inc(&tag->usage);
up_write(&fscache_addremove_sem);
kfree(xtag);
return tag;
}
}
list_add_tail(&xtag->link, &fscache_cache_tag_list);
up_write(&fscache_addremove_sem);
return xtag;
}
/*
* release a reference to a cache tag
*/
void __fscache_release_cache_tag(struct fscache_cache_tag *tag)
{
if (tag != ERR_PTR(-ENOMEM)) {
down_write(&fscache_addremove_sem);
if (atomic_dec_and_test(&tag->usage))
list_del_init(&tag->link);
else
tag = NULL;
up_write(&fscache_addremove_sem);
kfree(tag);
}
}
/*
* select a cache in which to store an object
* - the cache addremove semaphore must be at least read-locked by the caller
* - the object will never be an index
*/
struct fscache_cache *fscache_select_cache_for_object(
struct fscache_cookie *cookie)
{
struct fscache_cache_tag *tag;
struct fscache_object *object;
struct fscache_cache *cache;
_enter("");
if (list_empty(&fscache_cache_list)) {
_leave(" = NULL [no cache]");
return NULL;
}
/* we check the parent to determine the cache to use */
spin_lock(&cookie->lock);
/* the first in the parent's backing list should be the preferred
* cache */
if (!hlist_empty(&cookie->backing_objects)) {
object = hlist_entry(cookie->backing_objects.first,
struct fscache_object, cookie_link);
cache = object->cache;
if (fscache_object_is_dying(object) ||
test_bit(FSCACHE_IOERROR, &cache->flags))
cache = NULL;
spin_unlock(&cookie->lock);
_leave(" = %p [parent]", cache);
return cache;
}
/* the parent is unbacked */
if (cookie->type != FSCACHE_COOKIE_TYPE_INDEX) {
/* cookie not an index and is unbacked */
spin_unlock(&cookie->lock);
_leave(" = NULL [cookie ub,ni]");
return NULL;
}
spin_unlock(&cookie->lock);
if (!cookie->def->select_cache)
goto no_preference;
/* ask the netfs for its preference */
tag = cookie->def->select_cache(cookie->parent->netfs_data,
cookie->netfs_data);
if (!tag)
goto no_preference;
if (tag == ERR_PTR(-ENOMEM)) {
_leave(" = NULL [nomem tag]");
return NULL;
}
if (!tag->cache) {
_leave(" = NULL [unbacked tag]");
return NULL;
}
if (test_bit(FSCACHE_IOERROR, &tag->cache->flags))
return NULL;
_leave(" = %p [specific]", tag->cache);
return tag->cache;
no_preference:
/* netfs has no preference - just select first cache */
cache = list_entry(fscache_cache_list.next,
struct fscache_cache, link);
_leave(" = %p [first]", cache);
return cache;
}
/**
* fscache_init_cache - Initialise a cache record
* @cache: The cache record to be initialised
* @ops: The cache operations to be installed in that record
* @idfmt: Format string to define identifier
* @...: sprintf-style arguments
*
* Initialise a record of a cache and fill in the name.
*
* See Documentation/filesystems/caching/backend-api.txt for a complete
* description.
*/
void fscache_init_cache(struct fscache_cache *cache,
const struct fscache_cache_ops *ops,
const char *idfmt,
...)
{
va_list va;
memset(cache, 0, sizeof(*cache));
cache->ops = ops;
va_start(va, idfmt);
vsnprintf(cache->identifier, sizeof(cache->identifier), idfmt, va);
va_end(va);
INIT_WORK(&cache->op_gc, fscache_operation_gc);
INIT_LIST_HEAD(&cache->link);
INIT_LIST_HEAD(&cache->object_list);
INIT_LIST_HEAD(&cache->op_gc_list);
spin_lock_init(&cache->object_list_lock);
spin_lock_init(&cache->op_gc_list_lock);
}
EXPORT_SYMBOL(fscache_init_cache);
/**
* fscache_add_cache - Declare a cache as being open for business
* @cache: The record describing the cache
* @ifsdef: The record of the cache object describing the top-level index
* @tagname: The tag describing this cache
*
* Add a cache to the system, making it available for netfs's to use.
*
* See Documentation/filesystems/caching/backend-api.txt for a complete
* description.
*/
int fscache_add_cache(struct fscache_cache *cache,
struct fscache_object *ifsdef,
const char *tagname)
{
struct fscache_cache_tag *tag;
BUG_ON(!cache->ops);
BUG_ON(!ifsdef);
cache->flags = 0;
ifsdef->event_mask =
((1 << NR_FSCACHE_OBJECT_EVENTS) - 1) &
~(1 << FSCACHE_OBJECT_EV_CLEARED);
__set_bit(FSCACHE_OBJECT_IS_AVAILABLE, &ifsdef->flags);
if (!tagname)
tagname = cache->identifier;
BUG_ON(!tagname[0]);
_enter("{%s.%s},,%s", cache->ops->name, cache->identifier, tagname);
/* we use the cache tag to uniquely identify caches */
tag = __fscache_lookup_cache_tag(tagname);
if (IS_ERR(tag))
goto nomem;
if (test_and_set_bit(FSCACHE_TAG_RESERVED, &tag->flags))
goto tag_in_use;
cache->kobj = kobject_create_and_add(tagname, fscache_root);
if (!cache->kobj)
goto error;
ifsdef->cookie = &fscache_fsdef_index;
ifsdef->cache = cache;
cache->fsdef = ifsdef;
down_write(&fscache_addremove_sem);
tag->cache = cache;
cache->tag = tag;
/* add the cache to the list */
list_add(&cache->link, &fscache_cache_list);
/* add the cache's netfs definition index object to the cache's
* list */
spin_lock(&cache->object_list_lock);
list_add_tail(&ifsdef->cache_link, &cache->object_list);
spin_unlock(&cache->object_list_lock);
fscache_objlist_add(ifsdef);
/* add the cache's netfs definition index object to the top level index
* cookie as a known backing object */
spin_lock(&fscache_fsdef_index.lock);
hlist_add_head(&ifsdef->cookie_link,
&fscache_fsdef_index.backing_objects);
atomic_inc(&fscache_fsdef_index.usage);
/* done */
spin_unlock(&fscache_fsdef_index.lock);
up_write(&fscache_addremove_sem);
pr_notice("Cache \"%s\" added (type %s)\n",
cache->tag->name, cache->ops->name);
kobject_uevent(cache->kobj, KOBJ_ADD);
_leave(" = 0 [%s]", cache->identifier);
return 0;
tag_in_use:
pr_err("Cache tag '%s' already in use\n", tagname);
__fscache_release_cache_tag(tag);
_leave(" = -EXIST");
return -EEXIST;
error:
__fscache_release_cache_tag(tag);
_leave(" = -EINVAL");
return -EINVAL;
nomem:
_leave(" = -ENOMEM");
return -ENOMEM;
}
EXPORT_SYMBOL(fscache_add_cache);
/**
* fscache_io_error - Note a cache I/O error
* @cache: The record describing the cache
*
* Note that an I/O error occurred in a cache and that it should no longer be
* used for anything. This also reports the error into the kernel log.
*
* See Documentation/filesystems/caching/backend-api.txt for a complete
* description.
*/
void fscache_io_error(struct fscache_cache *cache)
{
if (!test_and_set_bit(FSCACHE_IOERROR, &cache->flags))
pr_err("Cache '%s' stopped due to I/O error\n",
cache->ops->name);
}
EXPORT_SYMBOL(fscache_io_error);
/*
* request withdrawal of all the objects in a cache
* - all the objects being withdrawn are moved onto the supplied list
*/
static void fscache_withdraw_all_objects(struct fscache_cache *cache,
struct list_head *dying_objects)
{
struct fscache_object *object;
while (!list_empty(&cache->object_list)) {
spin_lock(&cache->object_list_lock);
if (!list_empty(&cache->object_list)) {
object = list_entry(cache->object_list.next,
struct fscache_object, cache_link);
list_move_tail(&object->cache_link, dying_objects);
_debug("withdraw %p", object->cookie);
/* This must be done under object_list_lock to prevent
* a race with fscache_drop_object().
*/
fscache_raise_event(object, FSCACHE_OBJECT_EV_KILL);
}
spin_unlock(&cache->object_list_lock);
cond_resched();
}
}
/**
* fscache_withdraw_cache - Withdraw a cache from the active service
* @cache: The record describing the cache
*
* Withdraw a cache from service, unbinding all its cache objects from the
* netfs cookies they're currently representing.
*
* See Documentation/filesystems/caching/backend-api.txt for a complete
* description.
*/
void fscache_withdraw_cache(struct fscache_cache *cache)
{
LIST_HEAD(dying_objects);
_enter("");
pr_notice("Withdrawing cache \"%s\"\n",
cache->tag->name);
/* make the cache unavailable for cookie acquisition */
if (test_and_set_bit(FSCACHE_CACHE_WITHDRAWN, &cache->flags))
BUG();
down_write(&fscache_addremove_sem);
list_del_init(&cache->link);
cache->tag->cache = NULL;
up_write(&fscache_addremove_sem);
/* make sure all pages pinned by operations on behalf of the netfs are
* written to disk */
fscache_stat(&fscache_n_cop_sync_cache);
cache->ops->sync_cache(cache);
fscache_stat_d(&fscache_n_cop_sync_cache);
/* dissociate all the netfs pages backed by this cache from the block
* mappings in the cache */
fscache_stat(&fscache_n_cop_dissociate_pages);
cache->ops->dissociate_pages(cache);
fscache_stat_d(&fscache_n_cop_dissociate_pages);
/* we now have to destroy all the active objects pertaining to this
* cache - which we do by passing them off to thread pool to be
* disposed of */
_debug("destroy");
fscache_withdraw_all_objects(cache, &dying_objects);
/* wait for all extant objects to finish their outstanding operations
* and go away */
_debug("wait for finish");
wait_event(fscache_cache_cleared_wq,
atomic_read(&cache->object_count) == 0);
_debug("wait for clearance");
wait_event(fscache_cache_cleared_wq,
list_empty(&cache->object_list));
_debug("cleared");
ASSERT(list_empty(&dying_objects));
kobject_put(cache->kobj);
clear_bit(FSCACHE_TAG_RESERVED, &cache->tag->flags);
fscache_release_cache_tag(cache->tag);
cache->tag = NULL;
_leave("");
}
EXPORT_SYMBOL(fscache_withdraw_cache);