linux-kernel - Re: [patch 15/26] Slab defrag: Support generic defragmentation for inode slab caches

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Message-Id: <20070626123709.211c67c4.akpm@linux-foundation.org>
Date:	Tue, 26 Jun 2007 12:37:09 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Christoph Lameter <clameter@....com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Pekka Enberg <penberg@...helsinki.fi>,
	suresh.b.siddha@...el.com
Subject: Re: [patch 15/26] Slab defrag: Support generic defragmentation for
 inode slab caches

On Tue, 26 Jun 2007 12:28:50 -0700 (PDT)
Christoph Lameter <clameter@....com> wrote:

> On Tue, 26 Jun 2007, Andrew Morton wrote:
> 
> > Yes, this is tricky stuff.  I have vague ancestral memories that the sort
> > of inode work which you refer to here can cause various deadlocks, lockdep
> > warnings and such nasties when if we attempt to call it from the wrong
> > context (ie: from within fs code).
> 
> Right. Michael's test flushed one such issue out.
> 
> > Possibly we could prevent that by skipping all this code if the caller
> > didn't have __GFP_FS.
> 
> There is no check in vmscan.c as I thought earlier.
> 
> 
> Slab defragmentation: Only perform slab defrag if __GFP_FS is clear
> 
> Avoids slab defragmentation be triggered from filesystem operations.
> 
> Signed-off-by: Christoph Lameter <clameter@....com>
> 
> ---
>  mm/vmscan.c |    5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> Index: linux-2.6.22-rc4-mm2/mm/vmscan.c
> ===================================================================
> --- linux-2.6.22-rc4-mm2.orig/mm/vmscan.c	2007-06-26 12:25:28.000000000 -0700
> +++ linux-2.6.22-rc4-mm2/mm/vmscan.c	2007-06-26 12:26:18.000000000 -0700
> @@ -233,8 +233,9 @@ unsigned long shrink_slab(unsigned long 
>  		shrinker->nr += total_scan;
>  	}
>  	up_read(&shrinker_rwsem);
> -	kmem_cache_defrag(sysctl_slab_defrag_ratio,
> -		zone ? zone_to_nid(zone) : -1);
> +	if (!(gfp_mask & __GFP_FS))
> +		kmem_cache_defrag(sysctl_slab_defrag_ratio,
> +			zone ? zone_to_nid(zone) : -1);
>  	return ret;
>  }

This is inverted: __GFP_FS is set if we may perform fs operations.
-
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