[RFC PATCH] slab: __GFP_NOWARN not being propagated from mempool_alloc()

[RFC PATCH] slab: __GFP_NOWARN not being propagated from mempool_alloc()

[Miklos Szeredi]

We see page allocation failure warnings on the mempool_alloc() path.
See this lkml posting for example:

http://lkml.org/lkml/2008/10/27/100

The cause is that on NUMA, alloc_slabmgmt() clears __GFP_NOWARN,
together with __GFP_THISNODE and __GFP_NORETRY.  But AFAICS it really
only wants to clear __GFP_THISNODE.

Does this patch looks good?

Warning: it's completely untested.

Miklos
---
 mm/slab.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Index: linux-2.6/mm/slab.c
===================================================================
--- linux-2.6.orig/mm/slab.c	2008-10-24 12:40:34.000000000 +0200
+++ linux-2.6/mm/slab.c	2008-11-24 22:17:04.000000000 +0100
@@ -2609,7 +2609,8 @@ static struct slab *alloc_slabmgmt(struc
 	if (OFF_SLAB(cachep)) {
 		/* Slab management obj is off-slab. */
 		slabp = kmem_cache_alloc_node(cachep->slabp_cache,
-					      local_flags & ~GFP_THISNODE, nodeid);
+					      local_flags & ~__GFP_THISNODE,
+					      nodeid);
 		if (!slabp)
 			return NULL;
 	} else {

Re: [RFC PATCH] slab: __GFP_NOWARN not being propagated from mempool_alloc()

[Pekka J Enberg]

On Mon, 24 Nov 2008, Miklos Szeredi wrote:
> We see page allocation failure warnings on the mempool_alloc() path.
> See this lkml posting for example:
> 
> http://lkml.org/lkml/2008/10/27/100
> 
> The cause is that on NUMA, alloc_slabmgmt() clears __GFP_NOWARN,
> together with __GFP_THISNODE and __GFP_NORETRY.  But AFAICS it really
> only wants to clear __GFP_THISNODE.
> 
> Does this patch looks good?

Yes, it does but looking at mm/slab.c history I think we want something 
like the following instead. Christoph?

P.S. First one to test it gets a fabulous prize of a Tested-by tag in the 
patch description! How cool is that?

		Pekka

>From 717b2d7bd2398e948d1dfbd2e83bd6a8403b68da Mon Sep 17 00:00:00 2001
From: Pekka Enberg <penberg@cs.helsinki.fi>
Date: Tue, 25 Nov 2008 00:33:28 +0200
Subject: [PATCH] slab: remove GFP_THISNODE clearing from alloc_slabmgmt()

Commit 6cb062296f73e74768cca2f3eaf90deac54de02d ("Categorize GFP flags")
left one call-site in alloc_slabmgmt() to clear GFP_THISNODE instead of
GFP_CONSTRAINT_MASK. Unfortunately, that ends up clearing __GFP_NOWARN
and __GFP_NORETRY as well which is not what we want. As the only caller
of alloc_slabmgmt() already clears GFP_CONSTRAINT_MASK before passing
local_flags to it, we can just remove the clearing of GFP_THISNODE.

This patch should fix spurious page allocation failure warnings on the
mempool_alloc() path. See the following URL for an example:

  http://lkml.org/lkml/2008/10/27/100

Reported-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
---
 mm/slab.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index 918f04f..98d3024 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2608,7 +2608,7 @@ static struct slab *alloc_slabmgmt(struct kmem_cache *cachep, void *objp,
 	if (OFF_SLAB(cachep)) {
 		/* Slab management obj is off-slab. */
 		slabp = kmem_cache_alloc_node(cachep->slabp_cache,
-					      local_flags & ~GFP_THISNODE, nodeid);
+					      local_flags, nodeid);
 		if (!slabp)
 			return NULL;
 	} else {
-- 
1.5.6.4

Re: [RFC PATCH] slab: __GFP_NOWARN not being propagated from mempool_alloc()

[Christoph Lameter]

On Tue, 25 Nov 2008, Pekka J Enberg wrote:

> Yes, it does but looking at mm/slab.c history I think we want something
> like the following instead. Christoph?

Right.

Re: [RFC PATCH] slab: __GFP_NOWARN not being propagated from mempool_alloc()

[Pekka Enberg]

On Tue, 25 Nov 2008, Pekka J Enberg wrote:
> > Yes, it does but looking at mm/slab.c history I think we want something
> > like the following instead. Christoph?

On Tue, 2008-11-25 at 12:58 -0600, Christoph Lameter wrote:
> Right.

OK, even though no tester showed up, I went ahead and merged my version
of the patch as it's a pretty obvious one-liner fix.

Re: [RFC PATCH] slab: __GFP_NOWARN not being propagated from mempool_alloc()

[Miklos Szeredi]

On Wed, 26 Nov 2008, Pekka Enberg wrote:
> On Tue, 25 Nov 2008, Pekka J Enberg wrote:
> > > Yes, it does but looking at mm/slab.c history I think we want something
> > > like the following instead. Christoph?
> 
> On Tue, 2008-11-25 at 12:58 -0600, Christoph Lameter wrote:
> > Right.
> 
> OK, even though no tester showed up, I went ahead and merged my version
> of the patch as it's a pretty obvious one-liner fix.

Thanks.  I merged your version in the suse tree as well, so there'll
be lots of testers :)

Miklos