mm: optimize put_mems_allowed() usage

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>

1 files changed, 2 insertions, 2 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index c01cb9fedb18..139b7462203b 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -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;