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

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Message-ID: <Pine.LNX.4.64.0706261223110.20457@schroedinger.engr.sgi.com>
Date:	Tue, 26 Jun 2007 12:28:50 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
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, 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;
 }
 
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