Re: [PATCH 1/7] memcg: sc.nr_to_reclaim should be initialized

[Balbir Singh <balbir@linux.vnet.ibm.com>]

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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