From d7365e783edb858279be1d03f61bc8d5d3383d90 Mon Sep 17 00:00:00 2001 From: Johannes Weiner Date: Wed, 29 Oct 2014 14:50:48 -0700 Subject: mm: memcontrol: fix missed end-writeback page accounting Commit 0a31bc97c80c ("mm: memcontrol: rewrite uncharge API") changed page migration to uncharge the old page right away. The page is locked, unmapped, truncated, and off the LRU, but it could race with writeback ending, which then doesn't unaccount the page properly: test_clear_page_writeback() migration wait_on_page_writeback() TestClearPageWriteback() mem_cgroup_migrate() clear PCG_USED mem_cgroup_update_page_stat() if (PageCgroupUsed(pc)) decrease memcg pages under writeback release pc->mem_cgroup->move_lock The per-page statistics interface is heavily optimized to avoid a function call and a lookup_page_cgroup() in the file unmap fast path, which means it doesn't verify whether a page is still charged before clearing PageWriteback() and it has to do it in the stat update later. Rework it so that it looks up the page's memcg once at the beginning of the transaction and then uses it throughout. The charge will be verified before clearing PageWriteback() and migration can't uncharge the page as long as that is still set. The RCU lock will protect the memcg past uncharge. As far as losing the optimization goes, the following test results are from a microbenchmark that maps, faults, and unmaps a 4GB sparse file three times in a nested fashion, so that there are two negative passes that don't account but still go through the new transaction overhead. There is no actual difference: old: 33.195102545 seconds time elapsed ( +- 0.01% ) new: 33.199231369 seconds time elapsed ( +- 0.03% ) The time spent in page_remove_rmap()'s callees still adds up to the same, but the time spent in the function itself seems reduced: # Children Self Command Shared Object Symbol old: 0.12% 0.11% filemapstress [kernel.kallsyms] [k] page_remove_rmap new: 0.12% 0.08% filemapstress [kernel.kallsyms] [k] page_remove_rmap Signed-off-by: Johannes Weiner Acked-by: Michal Hocko Cc: Vladimir Davydov Cc: [3.17.x] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/memcontrol.h | 58 ++++++++++++++-------------------------------- 1 file changed, 17 insertions(+), 41 deletions(-) (limited to 'include') diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 19df5d857411..6b75640ef5ab 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -139,48 +139,23 @@ static inline bool mem_cgroup_disabled(void) return false; } -void __mem_cgroup_begin_update_page_stat(struct page *page, bool *locked, - unsigned long *flags); - -extern atomic_t memcg_moving; - -static inline void mem_cgroup_begin_update_page_stat(struct page *page, - bool *locked, unsigned long *flags) -{ - if (mem_cgroup_disabled()) - return; - rcu_read_lock(); - *locked = false; - if (atomic_read(&memcg_moving)) - __mem_cgroup_begin_update_page_stat(page, locked, flags); -} - -void __mem_cgroup_end_update_page_stat(struct page *page, - unsigned long *flags); -static inline void mem_cgroup_end_update_page_stat(struct page *page, - bool *locked, unsigned long *flags) -{ - if (mem_cgroup_disabled()) - return; - if (*locked) - __mem_cgroup_end_update_page_stat(page, flags); - rcu_read_unlock(); -} - -void mem_cgroup_update_page_stat(struct page *page, - enum mem_cgroup_stat_index idx, - int val); - -static inline void mem_cgroup_inc_page_stat(struct page *page, +struct mem_cgroup *mem_cgroup_begin_page_stat(struct page *page, bool *locked, + unsigned long *flags); +void mem_cgroup_end_page_stat(struct mem_cgroup *memcg, bool locked, + unsigned long flags); +void mem_cgroup_update_page_stat(struct mem_cgroup *memcg, + enum mem_cgroup_stat_index idx, int val); + +static inline void mem_cgroup_inc_page_stat(struct mem_cgroup *memcg, enum mem_cgroup_stat_index idx) { - mem_cgroup_update_page_stat(page, idx, 1); + mem_cgroup_update_page_stat(memcg, idx, 1); } -static inline void mem_cgroup_dec_page_stat(struct page *page, +static inline void mem_cgroup_dec_page_stat(struct mem_cgroup *memcg, enum mem_cgroup_stat_index idx) { - mem_cgroup_update_page_stat(page, idx, -1); + mem_cgroup_update_page_stat(memcg, idx, -1); } unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order, @@ -315,13 +290,14 @@ mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p) { } -static inline void mem_cgroup_begin_update_page_stat(struct page *page, +static inline struct mem_cgroup *mem_cgroup_begin_page_stat(struct page *page, bool *locked, unsigned long *flags) { + return NULL; } -static inline void mem_cgroup_end_update_page_stat(struct page *page, - bool *locked, unsigned long *flags) +static inline void mem_cgroup_end_page_stat(struct mem_cgroup *memcg, + bool locked, unsigned long flags) { } @@ -343,12 +319,12 @@ static inline bool mem_cgroup_oom_synchronize(bool wait) return false; } -static inline void mem_cgroup_inc_page_stat(struct page *page, +static inline void mem_cgroup_inc_page_stat(struct mem_cgroup *memcg, enum mem_cgroup_stat_index idx) { } -static inline void mem_cgroup_dec_page_stat(struct page *page, +static inline void mem_cgroup_dec_page_stat(struct mem_cgroup *memcg, enum mem_cgroup_stat_index idx) { } -- cgit v1.2.3