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    SubjectRe: [patch 5/8] mm: memcg: remove unneeded checks from newpage_charge()
    On Thu, Nov 24, 2011 at 09:04:43AM +0900, KAMEZAWA Hiroyuki wrote:
    > On Wed, 23 Nov 2011 16:42:28 +0100
    > Johannes Weiner <hannes@cmpxchg.org> wrote:
    >
    > > From: Johannes Weiner <jweiner@redhat.com>
    > >
    > > All callsites pass in freshly allocated pages and a valid mm. As a
    > > result, all checks pertaining the page's mapcount, page->mapping or
    > > the fallback to init_mm are unneeded.
    > >
    > > Signed-off-by: Johannes Weiner <jweiner@redhat.com>
    >
    > Hmm, it's true now. But for making clear our assumption to all readers of code,
    >
    > could you add
    > VM_BUG_ON(!mm || page_mapped(page) || (page->mapping && !PageAnon(page)) ?

    Of course. Please find the delta patch below. I broke them up into
    three separate checks to make the problem easier to find if the BUG
    triggers.

    > Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

    Thank you.

    ---
    From: Johannes Weiner <jweiner@redhat.com>
    Subject: mm: memcg: remove unneeded checks from newpage_charge() fix

    Document page state assumptions and catch if they are violated in
    newpage_charge().

    Signed-off-by: Johannes Weiner <jweiner@redhat.com>
    ---
    mm/memcontrol.c | 3 +++
    1 files changed, 3 insertions(+), 0 deletions(-)

    diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    index 0d10be4..f338018 100644
    --- a/mm/memcontrol.c
    +++ b/mm/memcontrol.c
    @@ -2679,6 +2679,9 @@ int mem_cgroup_newpage_charge(struct page *page,
    {
    if (mem_cgroup_disabled())
    return 0;
    + VM_BUG_ON(page_mapped(page));
    + VM_BUG_ON(page->mapping && !PageAnon(page));
    + VM_BUG_ON(!mm);
    return mem_cgroup_charge_common(page, mm, gfp_mask,
    MEM_CGROUP_CHARGE_TYPE_MAPPED);
    }
    --
    1.7.6.4

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