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

To: Alex Elder <aelder@xxxxxxx>
Subject: Re: [patch] xfs: properly account for reclaimed inodes
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Mon, 4 Oct 2010 18:19:04 +1100
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>, xfs@xxxxxxxxxxx, John Hawley <warthog9@xxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, stable@xxxxxxxxxx
In-reply-to: <1285953443.2422.4.camel@doink>
References: <20101001074354.GF2618@xxxxxxxxxxx> <1285953443.2422.4.camel@doink>
User-agent: Mutt/1.5.20 (2009-06-14)
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@xxxxxxxxxxx>
> > Cc: stable@xxxxxxxxxx
> 
> 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@xxxxxxx>

Alex, can you push this to Linus ASAP? This needs to go back to
stable kernels as well..

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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