linux-kernel - Re: [PATCH 02/15] mm: sl[au]b: Add knowledge of PFMEMALLOC reserve pages

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Date:	Fri, 10 Feb 2012 16:07:57 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Mel Gorman <mgorman@...e.de>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>,
	Linux-Netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>, Neil Brown <neilb@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH 02/15] mm: sl[au]b: Add knowledge of PFMEMALLOC reserve
 pages

Proposal for a patch for slub to move the pfmemalloc handling out of the
fastpath by simply not assigning a per cpu slab when pfmemalloc processing
is going on.



Subject: [slub] Fix so that no mods are required for the fast path

Remove the check for pfmemalloc from the alloc hotpath and put the logic after
the election of a new per cpu slab.

For a pfmemalloc page do not use the fast path but force use of the slow
path (which is also used for the debug case).

Signed-off-by: Christoph Lameter <cl@...ux.com>


---
 mm/slub.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c	2012-02-10 09:58:13.066125970 -0600
+++ linux-2.6/mm/slub.c	2012-02-10 10:06:07.114113000 -0600
@@ -2273,11 +2273,12 @@ new_slab:
 		}
 	}

-	if (likely(!kmem_cache_debug(s)))
+	if (likely(!kmem_cache_debug(s) && pfmemalloc_match(c, gfpflags)))
 		goto load_freelist;

+
 	/* Only entered in the debug case */
-	if (!alloc_debug_processing(s, c->page, object, addr))
+	if (kmem_cache_debug(s) && !alloc_debug_processing(s, c->page, object, addr))
 		goto new_slab;	/* Slab failed checks. Next slab needed */

 	c->freelist = get_freepointer(s, object);
@@ -2327,8 +2328,7 @@ redo:
 	barrier();

 	object = c->freelist;
-	if (unlikely(!object || !node_match(c, node) ||
-					!pfmemalloc_match(c, gfpflags)))
+	if (unlikely(!object || !node_match(c, node)))
 		object = __slab_alloc(s, gfpflags, node, addr, c);

 	else {
--
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