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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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4
mm/hugetlb.c
View file

@ -540,7 +540,7 @@ static struct page *dequeue_huge_page_vma(struct hstate *h,
goto err;
retry_cpuset:
cpuset_mems_cookie = get_mems_allowed();
cpuset_mems_cookie = read_mems_allowed_begin();
zonelist = huge_zonelist(vma, address,
htlb_alloc_mask(h), &mpol, &nodemask);
@ -562,7 +562,7 @@ retry_cpuset:
}
mpol_cond_put(mpol);
if (unlikely(!put_mems_allowed(cpuset_mems_cookie) && !page))
if (unlikely(!page && read_mems_allowed_retry(cpuset_mems_cookie)))
goto retry_cpuset;
return page;