On Thu 05-07-12 02:45:02, Johannes Weiner wrote:
> 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@xxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
> ---
> mm/memcontrol.c | 17 ++++++++++++-----
> 1 files changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index a8bf86a..d3701cd 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2471,11 +2471,7 @@ 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.
> @@ -2740,8 +2736,19 @@ 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
>
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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