From 5091b74a95d447e34530e713a8971450a45498b3 Mon Sep 17 00:00:00 2001 From: Christoph Lameter Date: Tue, 31 Jul 2012 16:44:00 -0700 Subject: [PATCH] mm: slub: optimise the SLUB fast path to avoid pfmemalloc checks 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@suse.de: Expanded changelog] Signed-off-by: Christoph Lameter Signed-off-by: Mel Gorman Cc: David Miller Cc: Neil Brown Cc: Peter Zijlstra Cc: Mike Christie Cc: Eric B Munson Cc: Eric Dumazet Cc: Sebastian Andrzej Siewior Cc: Mel Gorman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/slub.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index c3f05e1599c..8f78e257703 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2281,11 +2281,11 @@ 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)); @@ -2337,8 +2337,7 @@ 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 { -- 2.20.1