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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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16
mm/slub.c
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@@ -1684,7 +1684,7 @@ static void *get_any_partial(struct kmem_cache *s, gfp_t flags,
return NULL;
do {
cpuset_mems_cookie = get_mems_allowed();
cpuset_mems_cookie = read_mems_allowed_begin();
zonelist = node_zonelist(slab_node(), flags);
for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {
struct kmem_cache_node *n;
@@ -1696,19 +1696,17 @@ static void *get_any_partial(struct kmem_cache *s, gfp_t flags,
object = get_partial_node(s, n, c, flags);
if (object) {
/*
* Return the object even if
* put_mems_allowed indicated that
* the cpuset mems_allowed was
* updated in parallel. It's a
* harmless race between the alloc
* and the cpuset update.
* Don't check read_mems_allowed_retry()
* here - if mems_allowed was updated in
* parallel, that was a harmless race
* between allocation and the cpuset
* update
*/
put_mems_allowed(cpuset_mems_cookie);
return object;
}
}
}
} while (!put_mems_allowed(cpuset_mems_cookie));
} while (read_mems_allowed_retry(cpuset_mems_cookie));
#endif
return NULL;
}