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    SubjectRe: [RFC][PATCH 1/4] memcg: fix for mem_cgroup_get_reclaim_stat_from_page
    On Fri, 9 Jan 2009 10:02:57 +0530
    Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

    > > pc = lookup_page_cgroup(page);
    > > + smp_rmb();
    >
    > Do you really need the read memory barrier?
    >
    Necessary.

    > > + if (!PageCgroupUsed(pc))
    > > + return NULL;
    > > +
    >
    > In this case we've hit a case where the page is valid and the pc is
    > not. This does fix the problem, but won't this impact us getting
    > correct reclaim stats and thus indirectly impact the working of
    > pressure?
    >
    - If retruns NULL, only global LRU's status is updated.

    Because this page is not belongs to any memcg, we cannot update
    any counters. But yes, your point is a concern.

    Maybe moving acitvate_page() to
    ==
    do_swap_page()
    {

    - activate_page()
    mem_cgroup_try_charge()..
    ....
    mem_cgroup_commit_charge()....
    ....
    + activate_page()
    }
    ==
    is necessary. How do you think, kosaki ?

    Thanks,
    -Kame



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