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Message-Id: <1342075232-29267-3-git-send-email-mgorman@suse.de> Date: Thu, 12 Jul 2012 07:40:18 +0100 From: Mel Gorman <mgorman@...e.de> To: Andrew Morton <akpm@...ux-foundation.org> Cc: 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>, Mike Christie <michaelc@...wisc.edu>, Eric B Munson <emunson@...bm.net>, Eric Dumazet <eric.dumazet@...il.com>, Sebastian Andrzej Siewior <sebastian@...akpoint.cc>, Mel Gorman <mgorman@...e.de> Subject: [PATCH 02/16] mm: slub: Optimise the SLUB fast path to avoid pfmemalloc checks From: Christoph Lameter <cl@...ux.com> This patch removes the check for pfmemalloc from the alloc hotpath and puts the logic after the election of a new per cpu slab. For a pfmemalloc page we do not use the fast path but force the use of the slow path which is also used for the debug case. This has the side-effect of weakening pfmemalloc processing in the following way; 1. A process that is allocating for network swap calls __slab_alloc. pfmemalloc_match is true so the freelist is loaded and c->freelist is now pointing to a pfmemalloc page. 2. A process that is attempting normal allocations calls slab_alloc, finds the pfmemalloc page on the freelist and uses it because it did not check pfmemalloc_match() The patch allows non-pfmemalloc allocations to use pfmemalloc pages with the kmalloc slabs being the most vunerable caches on the grounds they are most likely to have a mix of pfmemalloc and !pfmemalloc requests. A later patch will still protect the system as processes will get throttled if the pfmemalloc reserves get depleted but performance will not degrade as smoothly. [mgorman@...e.de: Expanded changelog] Signed-off-by: Christoph Lameter <cl@...ux.com> Signed-off-by: Mel Gorman <mgorman@...e.de> --- mm/slub.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index 98fecc2..8e2a2f3 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2287,11 +2287,11 @@ new_slab: } page = c->page; - if (likely(!kmem_cache_debug(s))) + if (likely(!kmem_cache_debug(s) && pfmemalloc_match(page, gfpflags))) goto load_freelist; /* Only entered in the debug case */ - if (!alloc_debug_processing(s, page, freelist, addr)) + if (kmem_cache_debug(s) && !alloc_debug_processing(s, page, freelist, addr)) goto new_slab; /* Slab failed checks. Next slab needed */ deactivate_slab(s, page, get_freepointer(s, freelist)); @@ -2343,8 +2343,7 @@ redo: object = c->freelist; page = c->page; - if (unlikely(!object || !node_match(page, node) - !pfmemalloc_match(page, gfpflags))) + if (unlikely(!object || !node_match(page, node))) object = __slab_alloc(s, gfpflags, node, addr, c); else { -- 1.7.9.2 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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