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mm: page_alloc: exclude unreclaimable allocations from zone fairness policy

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Dave Hansen noted a regression in a microbenchmark that loops around
open() and close() on an 8-node NUMA machine and bisected it down to
commit 81c0a2bb51 ("mm: page_alloc: fair zone allocator policy").
That change forces the slab allocations of the file descriptor to spread
out to all 8 nodes, causing remote references in the page allocator and
slab.

The round-robin policy is only there to provide fairness among memory
allocations that are reclaimed involuntarily based on pressure in each
zone.  It does not make sense to apply it to unreclaimable kernel
allocations that are freed manually, in this case instantly after the
allocation, and incur the remote reference costs twice for no reason.

Only round-robin allocations that are usually freed through page reclaim
or slab shrinking.

Bisected by Dave Hansen.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Johannes Weiner 2013-12-18 17:08:47 -08:00 committed by Linus Torvalds
parent b0943d61b8
commit 73f038b863
1 changed files with 2 additions and 1 deletions
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3
mm/page_alloc.c
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@ -1920,7 +1920,8 @@ zonelist_scan:
* back to remote zones that do not partake in the
* fairness round-robin cycle of this zonelist.
*/
if (alloc_flags & ALLOC_WMARK_LOW) {
if ((alloc_flags & ALLOC_WMARK_LOW) &&
(gfp_mask & GFP_MOVABLE_MASK)) {
if (zone_page_state(zone, NR_ALLOC_BATCH) <= 0)
continue;
if (zone_reclaim_mode &&