From: "Hans-Peter Jansen" <hpj@urpla.net>
To: Dave Chinner <david@fromorbit.com>
Subject: Re: 2.6.34-rc3: simple du (on a big xfs tree) triggers oom killer [bisected: 57817c68229984818fea9e614d6f95249c3fb098]
Date: Thu, 8 Apr 2010 00:02:20 +0200
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On Wednesday 07 April 2010, 03:45:33 Dave Chinner wrote:
>
> However, if the memory pressure is purely inode cache (creating zero
> length files or read-only traversal), then the OOM killer kicks a
> while after the slab cache fills memory.  This doesn't need highmem;
> I used a x86_64 kernel on a VM w/ 1GB RAM to reliably reproduce
> this.  I'll add zero length file tests and traversals to my low
> memory testing.

I'm glad, that you're able to reproduce it. My initial failure was during 
disk to disk backup (with a simple cp -al & rsync combination).

> The best way to fix this, I think, is to trigger a shrinker callback
> when memory is low to run the background inode reclaim. The problem
> is that these inode caches and the reclaim state are per-filesystem,
> not global state, and the current shrinker interface only works with
> global state.
>
> Hence there are two patches to this fix - the first adds a context
> to the shrinker callout, and the second adds the XFS infrastructure
> to track the number of reclaimable inodes per filesystem and
> register/unregister shrinkers for each filesystem.

I see, the first one will be interesting to get into mainline, given the 
number of projects, that are involved. 

> With these patches, my reproducable test case which locked the
> machine up with a OOM panic in a couple of minutes has been running
> for over half an hour. I have much more confidence in this change
> with limited testing than the reverting of the background inode
> reclaim as the revert introduces
>
> The patches below apply to the xfs-dev tree, which is currently at
> 34-rc1. If they don't apply, let me know and I'll redo them against
> a vanilla kernel tree. Can you test them to see if the problem goes
> away? If the problem is fixed, I'll push them for a proper review
> cycle...

Of course, you did the original patch for a reason... Therefor I would love 
to test your patches. I've tried to apply them to 2.6.33.2, but after 
fixing the same reject as noted below, I'm stuck here:

/usr/src/packages/BUILD/kernel-default-2.6.33.2/linux-2.6.33/fs/xfs/linux-2.6/xfs_sync.c: 
In function 'xfs_reclaim_inode_shrink':
/usr/src/packages/BUILD/kernel-default-2.6.33.2/linux-2.6.33/fs/xfs/linux-2.6/xfs_sync.c:805: 
error: implicit declaration of function 'xfs_perag_get'
/usr/src/packages/BUILD/kernel-default-2.6.33.2/linux-2.6.33/fs/xfs/linux-2.6/xfs_sync.c:805: 
warning: assignment makes pointer from integer without a cast
/usr/src/packages/BUILD/kernel-default-2.6.33.2/linux-2.6.33/fs/xfs/linux-2.6/xfs_sync.c:807: 
error: implicit declaration of function 'xfs_perag_put'

Now I see, that there happened a rename of the offending functions, but also 
they've grown a radix_tree structure and locking. How do I handle that?

BTW, your patches do not apply to Linus' current git tree either:
patching file fs/xfs/quota/xfs_qm.c
Hunk #1 succeeded at 72 (offset 3 lines).
Hunk #2 FAILED at 2120.
1 out of 2 hunks FAILED -- saving rejects to file fs/xfs/quota/xfs_qm.c.rej
I'm able to resolve this, but 2.6.34-current does give me some other 
trouble, that I need to get by (PS2 keyboard stops working eventually)..

Anyway, thanks for your great support, Dave. This is much appreciated.

Cheers,
Pete
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