[PATCH] memcg: nano-optimize VM_BUG_ON in uncharge_page

[Michal Hocko]

Even though VM_BUG* is usually not compiled in there are systems which
enable CONFIG_DEBUG_VM by default. VM_BUG_ON_PAGE in uncharge_page is
not very optimal for the normal case. All pages should have counter==0
so that is the first thing to check. is_zone_device_page is nicely
noop if ZONE_DEVICE is not compiled in and finally HW poison pages
should be least probable. So reorder the check to bail out as early as
possible on normal case.

Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
---
 mm/memcontrol.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ae37b5624eb2..d5f3a62887cf 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5658,8 +5658,8 @@ static void uncharge_batch(const struct uncharge_gather *ug)
 static void uncharge_page(struct page *page, struct uncharge_gather *ug)
 {
 	VM_BUG_ON_PAGE(PageLRU(page), page);
-	VM_BUG_ON_PAGE(!PageHWPoison(page) && !is_zone_device_page(page) &&
-			page_count(page), page);
+	VM_BUG_ON_PAGE(page_count(page) && !is_zone_device_page(page) &&
+			!PageHWPoison(page) , page);
 
 	if (!page->mem_cgroup)
 		return;
-- 
2.14.1

-- 
Michal Hocko
SUSE Labs