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    SubjectRe: [BUGFIX][PATCH 1/5] memcg use correct scan number at reclaim
    On Thu, 12 Mar 2009 09:19:18 +0530
    Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

    > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-03-12 09:55:16]:
    >
    > > Andrew, this [1/5] is a bug fix, others are not.
    > >
    > > ==
    > > From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    > >
    > > Even when page reclaim is under mem_cgroup, # of scan page is determined by
    > > status of global LRU. Fix that.
    > >
    > > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    > > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    > > ---
    > > mm/vmscan.c | 2 +-
    > > 1 file changed, 1 insertion(+), 1 deletion(-)
    > >
    > > Index: mmotm-2.6.29-Mar10/mm/vmscan.c
    > > ===================================================================
    > > --- mmotm-2.6.29-Mar10.orig/mm/vmscan.c
    > > +++ mmotm-2.6.29-Mar10/mm/vmscan.c
    > > @@ -1470,7 +1470,7 @@ static void shrink_zone(int priority, st
    > > int file = is_file_lru(l);
    > > int scan;
    > >
    > > - scan = zone_page_state(zone, NR_LRU_BASE + l);
    > > + scan = zone_nr_pages(zone, sc, l);
    >
    > I have the exact same patch in my patch queue. BTW, mem_cgroup_zone_nr_pages is
    > buggy. We don't hold any sort of lock while extracting
    > MEM_CGROUP_ZSTAT (ideally we need zone->lru_lock). Without that how do
    > we guarantee that MEM_CGRUP_ZSTAT is not changing at the same time as
    > we are reading it?
    >
    Is it big problem ? We don't need very precise value and ZSTAT just have
    increment/decrement. So, I tend to ignore this small race.
    (and it's unsigned long, not long long.)

    Thanks,
    -Kame


    > > if (priority) {
    > > scan >>= priority;
    > > scan = (scan * percent[file]) / 100;
    > >
    > >
    >
    > --
    > Balbir
    >



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