Messages in this thread Patch in this message | | | From | Johannes Weiner <> | Subject | [patch 09/10] mm: memcg: only check swap cache pages for repeated charging | Date | Wed, 11 Jul 2012 19:02:21 +0200 |
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Only anon and shmem pages in the swap cache are attempted to be charged multiple times, from every swap pte fault or from shmem_unuse(). No other pages require checking PageCgroupUsed().
Charging pages in the swap cache is also serialized by the page lock, and since both the try_charge and commit_charge are called under the same page lock section, the PageCgroupUsed() check might as well happen before the counter charging, let alone reclaim.
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Acked-by: Michal Hocko <mhocko@suse.cz> --- mm/memcontrol.c | 17 ++++++++++++----- 1 files changed, 12 insertions(+), 5 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 36e6d73..9433bff 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2539,11 +2539,7 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg, bool anon; lock_page_cgroup(pc); - if (unlikely(PageCgroupUsed(pc))) { - unlock_page_cgroup(pc); - __mem_cgroup_cancel_charge(memcg, nr_pages); - return; - } + VM_BUG_ON(PageCgroupUsed(pc)); /* * we don't need page_cgroup_lock about tail pages, becase they are not * accessed by any other context at this point. @@ -2808,8 +2804,19 @@ static int __mem_cgroup_try_charge_swapin(struct mm_struct *mm, struct mem_cgroup **memcgp) { struct mem_cgroup *memcg; + struct page_cgroup *pc; int ret; + pc = lookup_page_cgroup(page); + /* + * Every swap fault against a single page tries to charge the + * page, bail as early as possible. shmem_unuse() encounters + * already charged pages, too. The USED bit is protected by + * the page lock, which serializes swap cache removal, which + * in turn serializes uncharging. + */ + if (PageCgroupUsed(pc)) + return 0; if (!do_swap_account) goto charge_cur_mm; /* -- 1.7.7.6
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