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>
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3bac76a..979378d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2739,7 +2739,7 @@
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 @@
* 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 @@
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;
}