On Wed 27-07-11 14:49:00, KAMEZAWA Hiroyuki wrote:
> memcg :avoid node fallback scan if possible.
>
> Now, try_to_free_pages() scans all zonelist because the page allocator
> should visit all zonelists...but that behavior is harmful for memcg.
> Memcg just scans memory because it hits limit...no memory shortage
> in pased zonelist.
>
> For example, with following unbalanced nodes
>
> Node 0 Node 1
> File 1G 0
> Anon 200M 200M
>
> memcg will cause swap-out from Node1 at every vmscan.
>
> Another example, assume 1024 nodes system.
> With 1024 node system, memcg will visit 1024 nodes
> pages per vmscan... This is overkilling.
>
> This is why memcg's victim node selection logic doesn't work
> as expected.
Previous patch adds nodemask filled by
mem_cgroup_select_victim_node. Shouldn't we rather limit that nodemask
to a victim node?
Or am I missing something?
The patch as is doesn't look nice it makes shrink_zones even more
memcg-hacky:
for_each_zone_zonelist_nodemask
if (scanning_global_lru(sc))
/.../
shrink_zone(priority, zone, sc);
if (!scanning_global_lru(sc))
/.../
>
> This patch is a help for stopping vmscan when we scanned enough.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> ---
> mm/vmscan.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> Index: mmotm-0710/mm/vmscan.c
> ===================================================================
> --- mmotm-0710.orig/mm/vmscan.c
> +++ mmotm-0710/mm/vmscan.c
> @@ -2058,6 +2058,16 @@ static void shrink_zones(int priority, s
> }
>
> shrink_zone(priority, zone, sc);
> + if (!scanning_global_lru(sc)) {
> + /*
> + * When we do scan for memcg's limit, it's bad to do
> + * fallback into more node/zones because there is no
> + * memory shortage. We quit as much as possible when
> + * we reache target.
> + */
> + if (sc->nr_to_reclaim <= sc->nr_reclaimed)
> + break;
> + }
> }
> }
>
>
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--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
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Czech Republic
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