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| author | Johannes Weiner <hannes@cmpxchg.org> | 2014-08-06 16:06:01 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2014-08-06 18:01:17 -0700 |
| commit | 9a2385eef9f28fb5260c48c45fc8fe01f1da70a6 (patch) | |
| tree | 1bd5538a1901519316b5b59f73dbf3ed508a8501 | |
| parent | 05b8430123359886ef6a4146fba384e30d771b3f (diff) | |
| download | linux-9a2385eef9f28fb5260c48c45fc8fe01f1da70a6.tar.gz linux-9a2385eef9f28fb5260c48c45fc8fe01f1da70a6.tar.bz2 linux-9a2385eef9f28fb5260c48c45fc8fe01f1da70a6.zip | |
mm: memcontrol: remove ordering between pc->mem_cgroup and PageCgroupUsed
There is a write barrier between setting pc->mem_cgroup and
PageCgroupUsed, which was added to allow LRU operations to lookup the
memcg LRU list of a page without acquiring the page_cgroup lock.
But ever since commit 38c5d72f3ebe ("memcg: simplify LRU handling by new
rule"), pages are ensured to be off-LRU while charging, so nobody else
is changing LRU state while pc->mem_cgroup is being written, and there
are no read barriers anymore.
Remove the unnecessary write barrier.
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | mm/memcontrol.c | 9 |
1 files changed, 0 insertions, 9 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 07908ea954b6..c31bc40a5827 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2795,14 +2795,6 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg, } pc->mem_cgroup = memcg; - /* - * We access a page_cgroup asynchronously without lock_page_cgroup(). - * Especially when a page_cgroup is taken from a page, pc->mem_cgroup - * is accessed after testing USED bit. To make pc->mem_cgroup visible - * before USED bit, we need memory barrier here. - * See mem_cgroup_add_lru_list(), etc. - */ - smp_wmb(); SetPageCgroupUsed(pc); if (lrucare) { @@ -3483,7 +3475,6 @@ void mem_cgroup_split_huge_fixup(struct page *head) for (i = 1; i < HPAGE_PMD_NR; i++) { pc = head_pc + i; pc->mem_cgroup = memcg; - smp_wmb();/* see __commit_charge() */ pc->flags = head_pc->flags & ~PCGF_NOCOPY_AT_SPLIT; } __this_cpu_sub(memcg->stat->count[MEM_CGROUP_STAT_RSS_HUGE], |