linux/fs/xfs/xfs_trans_ail.c
David Chinner 7ee49acfe5 [XFS] correctly select first log item to push
Under heavy metadata load we are seeing log hangs. The AIL has items in it
ready to be pushed, and they are within the push target window. However,
we are not pushing them when the last pushed LSN is less than the LSN of
the first log item on the AIL. This is a regression introduced by the AIL
push cursor modifications.

SGI-PV: 987246

SGI-Modid: xfs-linux-melb:xfs-kern:32409a

Signed-off-by: David Chinner <david@fromorbit.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>
2008-10-30 18:26:51 +11:00

733 lines
18 KiB
C

/*
* Copyright (c) 2000-2002,2005 Silicon Graphics, Inc.
* Copyright (c) 2008 Dave Chinner
* All Rights Reserved.
*
* 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.
*
* This program is distributed in the hope that it would be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include "xfs.h"
#include "xfs_fs.h"
#include "xfs_types.h"
#include "xfs_log.h"
#include "xfs_inum.h"
#include "xfs_trans.h"
#include "xfs_sb.h"
#include "xfs_ag.h"
#include "xfs_dmapi.h"
#include "xfs_mount.h"
#include "xfs_trans_priv.h"
#include "xfs_error.h"
STATIC void xfs_ail_insert(struct xfs_ail *, xfs_log_item_t *);
STATIC xfs_log_item_t * xfs_ail_delete(struct xfs_ail *, xfs_log_item_t *);
STATIC xfs_log_item_t * xfs_ail_min(struct xfs_ail *);
STATIC xfs_log_item_t * xfs_ail_next(struct xfs_ail *, xfs_log_item_t *);
#ifdef DEBUG
STATIC void xfs_ail_check(struct xfs_ail *, xfs_log_item_t *);
#else
#define xfs_ail_check(a,l)
#endif /* DEBUG */
/*
* This is called by the log manager code to determine the LSN
* of the tail of the log. This is exactly the LSN of the first
* item in the AIL. If the AIL is empty, then this function
* returns 0.
*
* We need the AIL lock in order to get a coherent read of the
* lsn of the last item in the AIL.
*/
xfs_lsn_t
xfs_trans_ail_tail(
struct xfs_ail *ailp)
{
xfs_lsn_t lsn;
xfs_log_item_t *lip;
spin_lock(&ailp->xa_lock);
lip = xfs_ail_min(ailp);
if (lip == NULL) {
lsn = (xfs_lsn_t)0;
} else {
lsn = lip->li_lsn;
}
spin_unlock(&ailp->xa_lock);
return lsn;
}
/*
* xfs_trans_push_ail
*
* This routine is called to move the tail of the AIL forward. It does this by
* trying to flush items in the AIL whose lsns are below the given
* threshold_lsn.
*
* the push is run asynchronously in a separate thread, so we return the tail
* of the log right now instead of the tail after the push. This means we will
* either continue right away, or we will sleep waiting on the async thread to
* do it's work.
*
* We do this unlocked - we only need to know whether there is anything in the
* AIL at the time we are called. We don't need to access the contents of
* any of the objects, so the lock is not needed.
*/
void
xfs_trans_ail_push(
struct xfs_ail *ailp,
xfs_lsn_t threshold_lsn)
{
xfs_log_item_t *lip;
lip = xfs_ail_min(ailp);
if (lip && !XFS_FORCED_SHUTDOWN(ailp->xa_mount)) {
if (XFS_LSN_CMP(threshold_lsn, ailp->xa_target) > 0)
xfsaild_wakeup(ailp, threshold_lsn);
}
}
/*
* AIL traversal cursor initialisation.
*
* The cursor keeps track of where our current traversal is up
* to by tracking the next ƣtem in the list for us. However, for
* this to be safe, removing an object from the AIL needs to invalidate
* any cursor that points to it. hence the traversal cursor needs to
* be linked to the struct xfs_ail so that deletion can search all the
* active cursors for invalidation.
*
* We don't link the push cursor because it is embedded in the struct
* xfs_ail and hence easily findable.
*/
STATIC void
xfs_trans_ail_cursor_init(
struct xfs_ail *ailp,
struct xfs_ail_cursor *cur)
{
cur->item = NULL;
if (cur == &ailp->xa_cursors)
return;
cur->next = ailp->xa_cursors.next;
ailp->xa_cursors.next = cur;
}
/*
* Set the cursor to the next item, because when we look
* up the cursor the current item may have been freed.
*/
STATIC void
xfs_trans_ail_cursor_set(
struct xfs_ail *ailp,
struct xfs_ail_cursor *cur,
struct xfs_log_item *lip)
{
if (lip)
cur->item = xfs_ail_next(ailp, lip);
}
/*
* Get the next item in the traversal and advance the cursor.
* If the cursor was invalidated (inidicated by a lip of 1),
* restart the traversal.
*/
struct xfs_log_item *
xfs_trans_ail_cursor_next(
struct xfs_ail *ailp,
struct xfs_ail_cursor *cur)
{
struct xfs_log_item *lip = cur->item;
if ((__psint_t)lip & 1)
lip = xfs_ail_min(ailp);
xfs_trans_ail_cursor_set(ailp, cur, lip);
return lip;
}
/*
* Now that the traversal is complete, we need to remove the cursor
* from the list of traversing cursors. Avoid removing the embedded
* push cursor, but use the fact it is alway present to make the
* list deletion simple.
*/
void
xfs_trans_ail_cursor_done(
struct xfs_ail *ailp,
struct xfs_ail_cursor *done)
{
struct xfs_ail_cursor *prev = NULL;
struct xfs_ail_cursor *cur;
done->item = NULL;
if (done == &ailp->xa_cursors)
return;
prev = &ailp->xa_cursors;
for (cur = prev->next; cur; prev = cur, cur = prev->next) {
if (cur == done) {
prev->next = cur->next;
break;
}
}
ASSERT(cur);
}
/*
* Invalidate any cursor that is pointing to this item. This is
* called when an item is removed from the AIL. Any cursor pointing
* to this object is now invalid and the traversal needs to be
* terminated so it doesn't reference a freed object. We set the
* cursor item to a value of 1 so we can distinguish between an
* invalidation and the end of the list when getting the next item
* from the cursor.
*/
STATIC void
xfs_trans_ail_cursor_clear(
struct xfs_ail *ailp,
struct xfs_log_item *lip)
{
struct xfs_ail_cursor *cur;
/* need to search all cursors */
for (cur = &ailp->xa_cursors; cur; cur = cur->next) {
if (cur->item == lip)
cur->item = (struct xfs_log_item *)
((__psint_t)cur->item | 1);
}
}
/*
* Return the item in the AIL with the current lsn.
* Return the current tree generation number for use
* in calls to xfs_trans_next_ail().
*/
xfs_log_item_t *
xfs_trans_ail_cursor_first(
struct xfs_ail *ailp,
struct xfs_ail_cursor *cur,
xfs_lsn_t lsn)
{
xfs_log_item_t *lip;
xfs_trans_ail_cursor_init(ailp, cur);
lip = xfs_ail_min(ailp);
if (lsn == 0)
goto out;
list_for_each_entry(lip, &ailp->xa_ail, li_ail) {
if (XFS_LSN_CMP(lip->li_lsn, lsn) >= 0)
goto out;
}
lip = NULL;
out:
xfs_trans_ail_cursor_set(ailp, cur, lip);
return lip;
}
/*
* Function that does the work of pushing on the AIL
*/
long
xfsaild_push(
struct xfs_ail *ailp,
xfs_lsn_t *last_lsn)
{
long tout = 1000; /* milliseconds */
xfs_lsn_t last_pushed_lsn = *last_lsn;
xfs_lsn_t target = ailp->xa_target;
xfs_lsn_t lsn;
xfs_log_item_t *lip;
int flush_log, count, stuck;
xfs_mount_t *mp = ailp->xa_mount;
struct xfs_ail_cursor *cur = &ailp->xa_cursors;
spin_lock(&ailp->xa_lock);
xfs_trans_ail_cursor_init(ailp, cur);
lip = xfs_trans_ail_cursor_first(ailp, cur, *last_lsn);
if (!lip || XFS_FORCED_SHUTDOWN(mp)) {
/*
* AIL is empty or our push has reached the end.
*/
xfs_trans_ail_cursor_done(ailp, cur);
spin_unlock(&ailp->xa_lock);
last_pushed_lsn = 0;
return tout;
}
XFS_STATS_INC(xs_push_ail);
/*
* While the item we are looking at is below the given threshold
* try to flush it out. We'd like not to stop until we've at least
* tried to push on everything in the AIL with an LSN less than
* the given threshold.
*
* However, we will stop after a certain number of pushes and wait
* for a reduced timeout to fire before pushing further. This
* prevents use from spinning when we can't do anything or there is
* lots of contention on the AIL lists.
*/
tout = 10;
lsn = lip->li_lsn;
flush_log = stuck = count = 0;
while ((XFS_LSN_CMP(lip->li_lsn, target) < 0)) {
int lock_result;
/*
* If we can lock the item without sleeping, unlock the AIL
* lock and flush the item. Then re-grab the AIL lock so we
* can look for the next item on the AIL. List changes are
* handled by the AIL lookup functions internally
*
* If we can't lock the item, either its holder will flush it
* or it is already being flushed or it is being relogged. In
* any of these case it is being taken care of and we can just
* skip to the next item in the list.
*/
lock_result = IOP_TRYLOCK(lip);
spin_unlock(&ailp->xa_lock);
switch (lock_result) {
case XFS_ITEM_SUCCESS:
XFS_STATS_INC(xs_push_ail_success);
IOP_PUSH(lip);
last_pushed_lsn = lsn;
break;
case XFS_ITEM_PUSHBUF:
XFS_STATS_INC(xs_push_ail_pushbuf);
IOP_PUSHBUF(lip);
last_pushed_lsn = lsn;
break;
case XFS_ITEM_PINNED:
XFS_STATS_INC(xs_push_ail_pinned);
stuck++;
flush_log = 1;
break;
case XFS_ITEM_LOCKED:
XFS_STATS_INC(xs_push_ail_locked);
last_pushed_lsn = lsn;
stuck++;
break;
case XFS_ITEM_FLUSHING:
XFS_STATS_INC(xs_push_ail_flushing);
last_pushed_lsn = lsn;
stuck++;
break;
default:
ASSERT(0);
break;
}
spin_lock(&ailp->xa_lock);
/* should we bother continuing? */
if (XFS_FORCED_SHUTDOWN(mp))
break;
ASSERT(mp->m_log);
count++;
/*
* Are there too many items we can't do anything with?
* If we we are skipping too many items because we can't flush
* them or they are already being flushed, we back off and
* given them time to complete whatever operation is being
* done. i.e. remove pressure from the AIL while we can't make
* progress so traversals don't slow down further inserts and
* removals to/from the AIL.
*
* The value of 100 is an arbitrary magic number based on
* observation.
*/
if (stuck > 100)
break;
lip = xfs_trans_ail_cursor_next(ailp, cur);
if (lip == NULL)
break;
lsn = lip->li_lsn;
}
xfs_trans_ail_cursor_done(ailp, cur);
spin_unlock(&ailp->xa_lock);
if (flush_log) {
/*
* If something we need to push out was pinned, then
* push out the log so it will become unpinned and
* move forward in the AIL.
*/
XFS_STATS_INC(xs_push_ail_flush);
xfs_log_force(mp, (xfs_lsn_t)0, XFS_LOG_FORCE);
}
if (!count) {
/* We're past our target or empty, so idle */
tout = 1000;
} else if (XFS_LSN_CMP(lsn, target) >= 0) {
/*
* We reached the target so wait a bit longer for I/O to
* complete and remove pushed items from the AIL before we
* start the next scan from the start of the AIL.
*/
tout += 20;
last_pushed_lsn = 0;
} else if ((stuck * 100) / count > 90) {
/*
* Either there is a lot of contention on the AIL or we
* are stuck due to operations in progress. "Stuck" in this
* case is defined as >90% of the items we tried to push
* were stuck.
*
* Backoff a bit more to allow some I/O to complete before
* continuing from where we were.
*/
tout += 10;
}
*last_lsn = last_pushed_lsn;
return tout;
} /* xfsaild_push */
/*
* This is to be called when an item is unlocked that may have
* been in the AIL. It will wake up the first member of the AIL
* wait list if this item's unlocking might allow it to progress.
* If the item is in the AIL, then we need to get the AIL lock
* while doing our checking so we don't race with someone going
* to sleep waiting for this event in xfs_trans_push_ail().
*/
void
xfs_trans_unlocked_item(
struct xfs_ail *ailp,
xfs_log_item_t *lip)
{
xfs_log_item_t *min_lip;
/*
* If we're forcibly shutting down, we may have
* unlocked log items arbitrarily. The last thing
* we want to do is to move the tail of the log
* over some potentially valid data.
*/
if (!(lip->li_flags & XFS_LI_IN_AIL) ||
XFS_FORCED_SHUTDOWN(ailp->xa_mount)) {
return;
}
/*
* This is the one case where we can call into xfs_ail_min()
* without holding the AIL lock because we only care about the
* case where we are at the tail of the AIL. If the object isn't
* at the tail, it doesn't matter what result we get back. This
* is slightly racy because since we were just unlocked, we could
* go to sleep between the call to xfs_ail_min and the call to
* xfs_log_move_tail, have someone else lock us, commit to us disk,
* move us out of the tail of the AIL, and then we wake up. However,
* the call to xfs_log_move_tail() doesn't do anything if there's
* not enough free space to wake people up so we're safe calling it.
*/
min_lip = xfs_ail_min(ailp);
if (min_lip == lip)
xfs_log_move_tail(ailp->xa_mount, 1);
} /* xfs_trans_unlocked_item */
/*
* Update the position of the item in the AIL with the new
* lsn. If it is not yet in the AIL, add it. Otherwise, move
* it to its new position by removing it and re-adding it.
*
* Wakeup anyone with an lsn less than the item's lsn. If the item
* we move in the AIL is the minimum one, update the tail lsn in the
* log manager.
*
* This function must be called with the AIL lock held. The lock
* is dropped before returning.
*/
void
xfs_trans_ail_update(
struct xfs_ail *ailp,
xfs_log_item_t *lip,
xfs_lsn_t lsn) __releases(ailp->xa_lock)
{
xfs_log_item_t *dlip = NULL;
xfs_log_item_t *mlip; /* ptr to minimum lip */
mlip = xfs_ail_min(ailp);
if (lip->li_flags & XFS_LI_IN_AIL) {
dlip = xfs_ail_delete(ailp, lip);
ASSERT(dlip == lip);
xfs_trans_ail_cursor_clear(ailp, dlip);
} else {
lip->li_flags |= XFS_LI_IN_AIL;
}
lip->li_lsn = lsn;
xfs_ail_insert(ailp, lip);
if (mlip == dlip) {
mlip = xfs_ail_min(ailp);
spin_unlock(&ailp->xa_lock);
xfs_log_move_tail(ailp->xa_mount, mlip->li_lsn);
} else {
spin_unlock(&ailp->xa_lock);
}
} /* xfs_trans_update_ail */
/*
* Delete the given item from the AIL. It must already be in
* the AIL.
*
* Wakeup anyone with an lsn less than item's lsn. If the item
* we delete in the AIL is the minimum one, update the tail lsn in the
* log manager.
*
* Clear the IN_AIL flag from the item, reset its lsn to 0, and
* bump the AIL's generation count to indicate that the tree
* has changed.
*
* This function must be called with the AIL lock held. The lock
* is dropped before returning.
*/
void
xfs_trans_ail_delete(
struct xfs_ail *ailp,
xfs_log_item_t *lip) __releases(ailp->xa_lock)
{
xfs_log_item_t *dlip;
xfs_log_item_t *mlip;
if (lip->li_flags & XFS_LI_IN_AIL) {
mlip = xfs_ail_min(ailp);
dlip = xfs_ail_delete(ailp, lip);
ASSERT(dlip == lip);
xfs_trans_ail_cursor_clear(ailp, dlip);
lip->li_flags &= ~XFS_LI_IN_AIL;
lip->li_lsn = 0;
if (mlip == dlip) {
mlip = xfs_ail_min(ailp);
spin_unlock(&ailp->xa_lock);
xfs_log_move_tail(ailp->xa_mount,
(mlip ? mlip->li_lsn : 0));
} else {
spin_unlock(&ailp->xa_lock);
}
}
else {
/*
* If the file system is not being shutdown, we are in
* serious trouble if we get to this stage.
*/
struct xfs_mount *mp = ailp->xa_mount;
spin_unlock(&ailp->xa_lock);
if (!XFS_FORCED_SHUTDOWN(mp)) {
xfs_cmn_err(XFS_PTAG_AILDELETE, CE_ALERT, mp,
"%s: attempting to delete a log item that is not in the AIL",
__func__);
xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
}
}
}
/*
* The active item list (AIL) is a doubly linked list of log
* items sorted by ascending lsn. The base of the list is
* a forw/back pointer pair embedded in the xfs mount structure.
* The base is initialized with both pointers pointing to the
* base. This case always needs to be distinguished, because
* the base has no lsn to look at. We almost always insert
* at the end of the list, so on inserts we search from the
* end of the list to find where the new item belongs.
*/
/*
* Initialize the doubly linked list to point only to itself.
*/
int
xfs_trans_ail_init(
xfs_mount_t *mp)
{
struct xfs_ail *ailp;
int error;
ailp = kmem_zalloc(sizeof(struct xfs_ail), KM_MAYFAIL);
if (!ailp)
return ENOMEM;
ailp->xa_mount = mp;
INIT_LIST_HEAD(&ailp->xa_ail);
spin_lock_init(&ailp->xa_lock);
error = xfsaild_start(ailp);
if (error)
goto out_free_ailp;
mp->m_ail = ailp;
return 0;
out_free_ailp:
kmem_free(ailp);
return error;
}
void
xfs_trans_ail_destroy(
xfs_mount_t *mp)
{
struct xfs_ail *ailp = mp->m_ail;
xfsaild_stop(ailp);
kmem_free(ailp);
}
/*
* Insert the given log item into the AIL.
* We almost always insert at the end of the list, so on inserts
* we search from the end of the list to find where the
* new item belongs.
*/
STATIC void
xfs_ail_insert(
struct xfs_ail *ailp,
xfs_log_item_t *lip)
/* ARGSUSED */
{
xfs_log_item_t *next_lip;
/*
* If the list is empty, just insert the item.
*/
if (list_empty(&ailp->xa_ail)) {
list_add(&lip->li_ail, &ailp->xa_ail);
return;
}
list_for_each_entry_reverse(next_lip, &ailp->xa_ail, li_ail) {
if (XFS_LSN_CMP(next_lip->li_lsn, lip->li_lsn) <= 0)
break;
}
ASSERT((&next_lip->li_ail == &ailp->xa_ail) ||
(XFS_LSN_CMP(next_lip->li_lsn, lip->li_lsn) <= 0));
list_add(&lip->li_ail, &next_lip->li_ail);
xfs_ail_check(ailp, lip);
return;
}
/*
* Delete the given item from the AIL. Return a pointer to the item.
*/
/*ARGSUSED*/
STATIC xfs_log_item_t *
xfs_ail_delete(
struct xfs_ail *ailp,
xfs_log_item_t *lip)
/* ARGSUSED */
{
xfs_ail_check(ailp, lip);
list_del(&lip->li_ail);
return lip;
}
/*
* Return a pointer to the first item in the AIL.
* If the AIL is empty, then return NULL.
*/
STATIC xfs_log_item_t *
xfs_ail_min(
struct xfs_ail *ailp)
/* ARGSUSED */
{
if (list_empty(&ailp->xa_ail))
return NULL;
return list_first_entry(&ailp->xa_ail, xfs_log_item_t, li_ail);
}
/*
* Return a pointer to the item which follows
* the given item in the AIL. If the given item
* is the last item in the list, then return NULL.
*/
STATIC xfs_log_item_t *
xfs_ail_next(
struct xfs_ail *ailp,
xfs_log_item_t *lip)
/* ARGSUSED */
{
if (lip->li_ail.next == &ailp->xa_ail)
return NULL;
return list_first_entry(&lip->li_ail, xfs_log_item_t, li_ail);
}
#ifdef DEBUG
/*
* Check that the list is sorted as it should be.
*/
STATIC void
xfs_ail_check(
struct xfs_ail *ailp,
xfs_log_item_t *lip)
{
xfs_log_item_t *prev_lip;
if (list_empty(&ailp->xa_ail))
return;
/*
* Check the next and previous entries are valid.
*/
ASSERT((lip->li_flags & XFS_LI_IN_AIL) != 0);
prev_lip = list_entry(lip->li_ail.prev, xfs_log_item_t, li_ail);
if (&prev_lip->li_ail != &ailp->xa_ail)
ASSERT(XFS_LSN_CMP(prev_lip->li_lsn, lip->li_lsn) <= 0);
prev_lip = list_entry(lip->li_ail.next, xfs_log_item_t, li_ail);
if (&prev_lip->li_ail != &ailp->xa_ail)
ASSERT(XFS_LSN_CMP(prev_lip->li_lsn, lip->li_lsn) >= 0);
#ifdef XFS_TRANS_DEBUG
/*
* Walk the list checking lsn ordering, and that every entry has the
* XFS_LI_IN_AIL flag set. This is really expensive, so only do it
* when specifically debugging the transaction subsystem.
*/
prev_lip = list_entry(&ailp->xa_ail, xfs_log_item_t, li_ail);
list_for_each_entry(lip, &ailp->xa_ail, li_ail) {
if (&prev_lip->li_ail != &ailp->xa_ail)
ASSERT(XFS_LSN_CMP(prev_lip->li_lsn, lip->li_lsn) <= 0);
ASSERT((lip->li_flags & XFS_LI_IN_AIL) != 0);
prev_lip = lip;
}
#endif /* XFS_TRANS_DEBUG */
}
#endif /* DEBUG */