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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>
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1 parent 202b510 commit d02d89d5e449de510d72d3ae2d72bbc8ac577aff Hugh Dickins committed with hnaz Jan 14, 2012
Showing with 21 additions and 30 deletions.
  1. +0 −10 mm/huge_memory.c
  2. +2 −10 mm/memcontrol.c
  3. +19 −10 mm/swap.c
View
10 mm/huge_memory.c
@@ -1201,7 +1201,6 @@ static void __split_huge_page_refcount(struct page *page)
int i;
unsigned long head_index = page->index;
struct zone *zone = page_zone(page);
- int zonestat;
int tail_count = 0;
/* prevent PageLRU to go away from under us, and freeze lru stats */
@@ -1289,15 +1288,6 @@ 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);
View
12 mm/memcontrol.c
@@ -1005,6 +1005,7 @@ void mem_cgroup_lru_del_list(struct page *page, enum lru_list lru)
VM_BUG_ON(!memcg);
mz = page_cgroup_zoneinfo(memcg, page);
/* huge page split is done under lru_lock. so, we have no races. */
+ VM_BUG_ON(MEM_CGROUP_ZSTAT(mz, lru) < (1 << compound_order(page)));
MEM_CGROUP_ZSTAT(mz, lru) -= 1 << compound_order(page);
}
@@ -2399,9 +2400,7 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg,
void mem_cgroup_split_huge_fixup(struct page *head)
{
struct page_cgroup *head_pc = lookup_page_cgroup(head);
- struct mem_cgroup_per_zone *mz;
struct page_cgroup *pc;
- enum lru_list lru;
int i;
if (mem_cgroup_disabled())
@@ -2412,15 +2411,8 @@ void mem_cgroup_split_huge_fixup(struct page *head)
smp_wmb();/* see __commit_charge() */
pc->flags = head_pc->flags & ~PCGF_NOCOPY_AT_SPLIT;
}
- /*
- * Tail pages will be added to LRU.
- * We hold lru_lock,then,reduce counter directly.
- */
- lru = page_lru(head);
- mz = page_cgroup_zoneinfo(head_pc->mem_cgroup, head);
- MEM_CGROUP_ZSTAT(mz, lru) -= HPAGE_PMD_NR - 1;
}
-#endif
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
/**
* mem_cgroup_move_account - move account of the page
View
29 mm/swap.c
@@ -658,6 +658,7 @@ 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)
@@ -674,8 +675,6 @@ 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;
@@ -685,18 +684,28 @@ 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]);
- __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)
{

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