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author | 2012-07-31 16:44:00 -0700 | |
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committer | 2012-07-31 18:42:45 -0700 | |
commit | 5091b74a95d447e34530e713a8971450a45498b3 (patch) | |
tree | 7761a47736e539f829e1d9fe18e11bb7109ec76b /mm | |
parent | mm: sl[au]b: add knowledge of PFMEMALLOC reserve pages (diff) | |
download | linux-5091b74a95d447e34530e713a8971450a45498b3.tar.gz linux-5091b74a95d447e34530e713a8971450a45498b3.tar.bz2 linux-5091b74a95d447e34530e713a8971450a45498b3.zip |
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 <cl@linux.com>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: David Miller <davem@davemloft.net>
Cc: Neil Brown <neilb@suse.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Christie <michaelc@cs.wisc.edu>
Cc: Eric B Munson <emunson@mgebm.net>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Cc: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r-- | mm/slub.c | 7 |
1 files changed, 3 insertions, 4 deletions
diff --git a/mm/slub.c b/mm/slub.c index c3f05e1599c0..8f78e2577031 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 { |