memcg: fix split_huge_page_refcounts()

This patch started off as a cleanup: __split_huge_page_refcounts() has to
cope with two scenarios, when the hugepage being split is already on LRU,
and when it is not; but why does it have to split that accounting across
three different sites?  Consolidate it in lru_add_page_tail(), handling
evictable and unevictable alike, and use standard add_page_to_lru_list()
when accounting is needed (when the head is not yet on LRU).

But a recent regression in -next, I guess the removal of PageCgroupAcctLRU
test from mem_cgroup_split_huge_fixup(), makes this now a necessary fix:
under load, the MEM_CGROUP_ZSTAT count was wrapping to a huge number,
messing up reclaim calculations and causing a freeze at rmdir of cgroup.

Add a VM_BUG_ON to mem_cgroup_lru_del_list() when we're about to wrap that
count - this has not been the only such incident.  Document that
lru_add_page_tail() is for Transparent HugePages by #ifdef around it.

Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 0 insertions, 10 deletions

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 76cc3f7dd4f0..b3ffc21ce801 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1229,7 +1229,6 @@ static void __split_huge_page_refcount(struct page *page)
 {
         int i;
         struct zone *zone = page_zone(page);
-        int zonestat;
         int tail_count = 0;
 
         /* prevent PageLRU to go away from under us, and freeze lru stats */
@@ -1317,15 +1316,6 @@ static void __split_huge_page_refcount(struct page *page)
         __dec_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES);
         __mod_zone_page_state(zone, NR_ANON_PAGES, HPAGE_PMD_NR);
 
-        /*
-         * A hugepage counts for HPAGE_PMD_NR pages on the LRU statistics,
-         * so adjust those appropriately if this page is on the LRU.
-         */
-        if (PageLRU(page)) {
-                zonestat = NR_LRU_BASE + page_lru(page);
-                __mod_zone_page_state(zone, zonestat, -(HPAGE_PMD_NR-1));
-        }
-
         ClearPageCompound(page);
         compound_unlock(page);
         spin_unlock_irq(&zone->lru_lock);