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, 19 insertions, 10 deletions

diff --git a/mm/swap.c b/mm/swap.c
index ddccf8e0b4ae..db6defaf2e55 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -650,6 +650,7 @@ void __pagevec_release(struct pagevec *pvec)
 
 EXPORT_SYMBOL(__pagevec_release);
 
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
 /* used by __split_huge_page_refcount() */
 void lru_add_page_tail(struct zone* zone,
 		       struct page *page, struct page *page_tail)
@@ -666,8 +667,6 @@ void lru_add_page_tail(struct zone* zone,
 	SetPageLRU(page_tail);
 
 	if (page_evictable(page_tail, NULL)) {
-		struct lruvec *lruvec;
-
 		if (PageActive(page)) {
 			SetPageActive(page_tail);
 			active = 1;
@@ -677,18 +676,28 @@ void lru_add_page_tail(struct zone* zone,
 			lru = LRU_INACTIVE_ANON;
 		}
 		update_page_reclaim_stat(zone, page_tail, file, active);
-		lruvec = mem_cgroup_lru_add_list(zone, page_tail, lru);
-		if (likely(PageLRU(page)))
-			list_add(&page_tail->lru, page->lru.prev);
-		else
-			list_add(&page_tail->lru, lruvec->lists[lru].prev);
-		__mod_zone_page_state(zone, NR_LRU_BASE + lru,
-				      hpage_nr_pages(page_tail));
 	} else {
 		SetPageUnevictable(page_tail);
-		add_page_to_lru_list(zone, page_tail, LRU_UNEVICTABLE);
+		lru = LRU_UNEVICTABLE;
+	}
+
+	if (likely(PageLRU(page)))
+		list_add_tail(&page_tail->lru, &page->lru);
+	else {
+		struct list_head *list_head;
+		/*
+		 * Head page has not yet been counted, as an hpage,
+		 * so we must account for each subpage individually.
+		 *
+		 * Use the standard add function to put page_tail on the list,
+		 * but then correct its position so they all end up in order.
+		 */
+		add_page_to_lru_list(zone, page_tail, lru);
+		list_head = page_tail->lru.prev;
+		list_move_tail(&page_tail->lru, list_head);
 	}
 }
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
 static void ____pagevec_lru_add_fn(struct page *page, void *arg)
 {