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mm: optimize put_mems_allowed() usage

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Since put_mems_allowed() is strictly optional, its a seqcount retry, we
don't need to evaluate the function if the allocation was in fact
successful, saving a smp_rmb some loads and comparisons on some relative
fast-paths.

Since the naming, get/put_mems_allowed() does suggest a mandatory
pairing, rename the interface, as suggested by Mel, to resemble the
seqcount interface.

This gives us: read_mems_allowed_begin() and read_mems_allowed_retry(),
where it is important to note that the return value of the latter call
is inverted from its previous incarnation.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Mel Gorman
2014-04-03 14:47:24 -07:00
committed by Linus Torvalds
parent 91ca918648
commit d26914d117
8 changed files with 38 additions and 39 deletions
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8
mm/page_alloc.c
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@@ -2739,7 +2739,7 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
return NULL;
retry_cpuset:
cpuset_mems_cookie = get_mems_allowed();
cpuset_mems_cookie = read_mems_allowed_begin();
/* The preferred zone is used for statistics later */
first_zones_zonelist(zonelist, high_zoneidx,
@@ -2777,7 +2777,7 @@ out:
* the mask is being updated. If a page allocation is about to fail,
* check if the cpuset changed during allocation and if so, retry.
*/
if (unlikely(!put_mems_allowed(cpuset_mems_cookie) && !page))
if (unlikely(!page && read_mems_allowed_retry(cpuset_mems_cookie)))
goto retry_cpuset;
memcg_kmem_commit_charge(page, memcg, order);
@@ -3045,9 +3045,9 @@ bool skip_free_areas_node(unsigned int flags, int nid)
goto out;
do {
cpuset_mems_cookie = get_mems_allowed();
cpuset_mems_cookie = read_mems_allowed_begin();
ret = !node_isset(nid, cpuset_current_mems_allowed);
} while (!put_mems_allowed(cpuset_mems_cookie));
} while (read_mems_allowed_retry(cpuset_mems_cookie));
out:
return ret;
}