[patch] xfs: properly account for reclaimed inodes

[Alex Elder]

On Fri, 2010-10-01 at 09:43 +0200, Johannes Weiner wrote:
> When marking an inode reclaimable, a per-AG counter is increased, the
> inode is tagged reclaimable in its per-AG tree, and, when this is the
> first reclaimable inode in the AG, the AG entry in the per-mount tree
> is also tagged.
> 
> When an inode is finally reclaimed, however, it is only deleted from
> the per-AG tree.  Neither the counter is decreased, nor is the parent
> tree's AG entry untagged properly.
> 
> Since the tags in the per-mount tree are not cleared, the inode
> shrinker iterates over all AGs that have had reclaimable inodes at one
> point in time.
> 
> The counters on the other hand signal an increasing amount of slab
> objects to reclaim.  Since "70e60ce xfs: convert inode shrinker to
> per-filesystem context" this is not a real issue anymore because the
> shrinker bails out after one iteration.
> 
> But the problem was observable on a machine running v2.6.34, where the
> reclaimable work increased and each process going into direct reclaim
> eventually got stuck on the xfs inode shrinking path, trying to scan
> several million objects.
> 
> Fix this by properly unwinding the reclaimable-state tracking of an
> inode when it is reclaimed.
> 
> Signed-off-by: Johannes Weiner <hannes at cmpxchg.org>
> Cc: stable at kernel.org

Yes, this looks right to me.  The state was correctly
adjusted in xfs_iget_cache_hit() when a RECLAIMABLE
inode is found in the cache, but it was not done when
reclaim completes.

Reviewed-by: Alex Elder <aelder at sgi.com>