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    SubjectRe: [patch 1/3] memcg: prevent endless loop when charging huge pages
    On Mon, 31 Jan 2011 15:03:53 +0100
    Johannes Weiner <hannes@cmpxchg.org> wrote:

    > The charging code can encounter a charge size that is bigger than a
    > regular page in two situations: one is a batched charge to fill the
    > per-cpu stocks, the other is a huge page charge.
    >
    > This code is distributed over two functions, however, and only the
    > outer one is aware of huge pages. In case the charging fails, the
    > inner function will tell the outer function to retry if the charge
    > size is bigger than regular pages--assuming batched charging is the
    > only case. And the outer function will retry forever charging a huge
    > page.
    >
    > This patch makes sure the inner function can distinguish between batch
    > charging and a single huge page charge. It will only signal another
    > attempt if batch charging failed, and go into regular reclaim when it
    > is called on behalf of a huge page.
    >
    > Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

    Thank you very much.

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

    > ---
    > mm/memcontrol.c | 11 +++++++++--
    > 1 files changed, 9 insertions(+), 2 deletions(-)
    >
    > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    > index d572102..73ea323 100644
    > --- a/mm/memcontrol.c
    > +++ b/mm/memcontrol.c
    > @@ -1837,8 +1837,15 @@ static int __mem_cgroup_do_charge(struct mem_cgroup *mem, gfp_t gfp_mask,
    > flags |= MEM_CGROUP_RECLAIM_NOSWAP;
    > } else
    > mem_over_limit = mem_cgroup_from_res_counter(fail_res, res);
    > -
    > - if (csize > PAGE_SIZE) /* change csize and retry */
    > + /*
    > + * csize can be either a huge page (HPAGE_SIZE), a batch of
    > + * regular pages (CHARGE_SIZE), or a single regular page
    > + * (PAGE_SIZE).
    > + *
    > + * Never reclaim on behalf of optional batching, retry with a
    > + * single page instead.
    > + */
    > + if (csize == CHARGE_SIZE)
    > return CHARGE_RETRY;
    >
    > if (!(gfp_mask & __GFP_WAIT))
    > --
    > 1.7.3.5
    >
    >



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