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    SubjectRe: [PATCH 1/7] memcg: sc.nr_to_reclaim should be initialized
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    On Fri, Jul 23, 2010 at 1:03 PM, KOSAKI Motohiro
    <kosaki.motohiro@jp.fujitsu.com> wrote:
    >> * KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> [2010-07-16 19:13:31]:
    >>
    >> > Currently, mem_cgroup_shrink_node_zone() initialize sc.nr_to_reclaim as 0.
    >> > It mean shrink_zone() only scan 32 pages and immediately return even if
    >> > it doesn't reclaim any pages.
    >> >
    >> > This patch fixes it.
    >> >
    >> > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    >> > ---
    >> >  mm/vmscan.c |    1 +
    >> >  1 files changed, 1 insertions(+), 0 deletions(-)
    >> >
    >> > diff --git a/mm/vmscan.c b/mm/vmscan.c
    >> > index 1691ad0..bd1d035 100644
    >> > --- a/mm/vmscan.c
    >> > +++ b/mm/vmscan.c
    >> > @@ -1932,6 +1932,7 @@ unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
    >> >                                             struct zone *zone, int nid)
    >> >  {
    >> >     struct scan_control sc = {
    >> > +           .nr_to_reclaim = SWAP_CLUSTER_MAX,
    >> >             .may_writepage = !laptop_mode,
    >> >             .may_unmap = 1,
    >> >             .may_swap = !noswap,
    >>
    >> Could you please do some additional testing on
    >>
    >> 1. How far does this push pages (in terms of when limit is hit)?
    >
    > 32 pages per mem_cgroup_shrink_node_zone().
    >
    > That said, the algorithm is here.
    >
    > 1. call mem_cgroup_largest_soft_limit_node()
    >   calculate largest cgroup
    > 2. call mem_cgroup_shrink_node_zone() and shrink 32 pages
    > 3. goto 1 if limit is still exceed.
    >
    > If it's not your intention, can you please your intended algorithm?

    We set it to 0, since we care only about a single page reclaim on
    hitting the limit. IIRC, in the past we saw an excessive pushback on
    reclaiming SWAP_CLUSTER_MAX pages, just wanted to check if you are
    seeing the same behaviour even now after your changes.

    Balbir
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