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    SubjectRe: [BUGFIX][PATCH 1/4] memcg: fix limit estimation at reclaim for hugepage
    On Fri, Jan 28, 2011 at 12:24:49PM +0900, KAMEZAWA Hiroyuki wrote:
    > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    >
    > Current memory cgroup's code tends to assume page_size == PAGE_SIZE
    > and arrangement for THP is not enough yet.
    >
    > This is one of fixes for supporing THP. This adds
    > mem_cgroup_check_margin() and checks whether there are required amount of
    > free resource after memory reclaim. By this, THP page allocation
    > can know whether it really succeeded or not and avoid infinite-loop
    > and hangup.
    >
    > Total fixes for do_charge()/reclaim memory will follow this patch.
    >
    > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    > ---
    > include/linux/res_counter.h | 11 +++++++++++
    > mm/memcontrol.c | 25 ++++++++++++++++++++++++-
    > 2 files changed, 35 insertions(+), 1 deletion(-)
    >
    > Index: mmotm-0125/include/linux/res_counter.h
    > ===================================================================
    > --- mmotm-0125.orig/include/linux/res_counter.h
    > +++ mmotm-0125/include/linux/res_counter.h
    > @@ -182,6 +182,17 @@ static inline bool res_counter_check_und
    > return ret;
    > }
    >
    > +static inline s64 res_counter_check_margin(struct res_counter *cnt)
    > +{
    > + s64 ret;
    > + unsigned long flags;
    > +
    > + spin_lock_irqsave(&cnt->lock, flags);
    > + ret = cnt->limit - cnt->usage;
    > + spin_unlock_irqrestore(&cnt->lock, flags);
    > + return ret;
    > +}

    This function does not check anything. You could name it
    res_counter_get_margin() e.g. But if you do that, I will complain
    that it's asymmetric to res_counter_check_under_limit(). And the
    result will be pretty close to my version...

    > @@ -1853,7 +1869,14 @@ static int __mem_cgroup_do_charge(struct
    > * Check the limit again to see if the reclaim reduced the
    > * current usage of the cgroup before giving up
    > */
    > - if (ret || mem_cgroup_check_under_limit(mem_over_limit))
    > + if (mem_cgroup_check_margin(mem_over_limit) >= csize)
    > + return CHARGE_RETRY;
    > +
    > + /*
    > + * If the charge size is a PAGE_SIZE, it's not hopeless while
    > + * we can reclaim a page.
    > + */
    > + if (csize == PAGE_SIZE && ret)
    > return CHARGE_RETRY;

    That makes sense.


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