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xfs: serialise inode reclaim within an AG

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Memory reclaim via shrinkers has a terrible habit of having N+M
concurrent shrinker executions (N = num CPUs, M = num kswapds) all
trying to shrink the same cache. When the cache they are all working
on is protected by a single spinlock, massive contention an
slowdowns occur.

Wrap the per-ag inode caches with a reclaim mutex to serialise
reclaim access to the AG. This will block concurrent reclaim in each
AG but still allow reclaim to scan multiple AGs concurrently. Allow
shrinkers to move on to the next AG if it can't get the lock, and if
we can't get any AG, then start blocking on locks.

To prevent reclaimers from continually scanning the same inodes in
each AG, add a cursor that tracks where the last reclaim got up to
and start from that point on the next reclaim. This should avoid
only ever scanning a small number of inodes at the satart of each AG
and not making progress. If we have a non-shrinker based reclaim
pass, ignore the cursor and reset it to zero once we are done.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Alex Elder <aelder@sgi.com>
This commit is contained in:
Dave Chinner
2010-09-27 11:09:51 +10:00
committed by Alex Elder
parent e3a20c0b02
commit 69b491c214
3 changed files with 33 additions and 0 deletions
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30
fs/xfs/linux-2.6/xfs_sync.c
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@@ -837,8 +837,12 @@ xfs_reclaim_inodes_ag(
int error = 0;
int last_error = 0;
xfs_agnumber_t ag;
int trylock = flags & SYNC_TRYLOCK;
int skipped;
restart:
ag = 0;
skipped = 0;
while ((pag = xfs_perag_get_tag(mp, ag, XFS_ICI_RECLAIM_TAG))) {
unsigned long first_index = 0;
int done = 0;
@@ -846,6 +850,15 @@ xfs_reclaim_inodes_ag(
ag = pag->pag_agno + 1;
if (trylock) {
if (!mutex_trylock(&pag->pag_ici_reclaim_lock)) {
skipped++;
continue;
}
first_index = pag->pag_ici_reclaim_cursor;
} else
mutex_lock(&pag->pag_ici_reclaim_lock);
do {
struct xfs_inode *batch[XFS_LOOKUP_BATCH];
int i;
@@ -898,8 +911,25 @@ xfs_reclaim_inodes_ag(
} while (nr_found && !done && *nr_to_scan > 0);
if (trylock && !done)
pag->pag_ici_reclaim_cursor = first_index;
else
pag->pag_ici_reclaim_cursor = 0;
mutex_unlock(&pag->pag_ici_reclaim_lock);
xfs_perag_put(pag);
}
/*
* if we skipped any AG, and we still have scan count remaining, do
* another pass this time using blocking reclaim semantics (i.e
* waiting on the reclaim locks and ignoring the reclaim cursors). This
* ensure that when we get more reclaimers than AGs we block rather
* than spin trying to execute reclaim.
*/
if (trylock && skipped && *nr_to_scan > 0) {
trylock = 0;
goto restart;
}
return XFS_ERROR(last_error);
}