Re: [patch] xfs: properly account for reclaimed inodes

[Johannes Weiner <hannes@cmpxchg.org>]

Hi,

On Mon, Oct 04, 2010 at 06:19:04PM +1100, Dave Chinner wrote:
> On Fri, Oct 01, 2010 at 12:17:23PM -0500, Alex Elder wrote:
> > 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@cmpxchg.org>
> > > Cc: stable@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@sgi.com>
> 
> Alex, can you push this to Linus ASAP? This needs to go back to
> stable kernels as well..

Here is my suggestion of a backport to .34.  Dave, Alex, do you
approve?

	Hannes

diff --git a/fs/xfs/xfs_iget.c b/fs/xfs/xfs_iget.c
index 6845db9..3314f2a 100644
--- a/fs/xfs/xfs_iget.c
+++ b/fs/xfs/xfs_iget.c
@@ -499,6 +499,7 @@ xfs_ireclaim(
 	write_lock(&pag->pag_ici_lock);
 	if (!radix_tree_delete(&pag->pag_ici_root, agino))
 		ASSERT(0);
+	pag->pag_ici_reclaimable--;
 	write_unlock(&pag->pag_ici_lock);
 	xfs_perag_put(pag);