Re: [PATCH mmotm] vmscan: handle may_swap more strictly (Re: [PATCH mmotm] vmscan: fix may_swap handling for memcg)

On Tue, Jun 9, 2009 at 4:58 PM, KOSAKI
Motohiro<kosaki.motohiro@xxxxxxxxxxxxxx> wrote:
Hi, KOSAKI.

As you know, this problem caused by if condition(priority) in shrink_zone.
Let me have a question.

Why do we have to prevent scan value calculation when the priority is zero ?
As I know, before split-lru, we didn't do it.

Is there any specific issue in case of the priority is zero ?

Yes.

example:

get_scan_ratio() return anon:80%, file=20%. and the system have
10000 anon pages and 10000 file pages.

shrink_zone() picked up 8000 anon pages and 2000 file pages.
it mean 8000 file pages aren't scanned at all.

Oops, it can makes OOM-killer although system have droppable file cache.

Hmm..Can that problem be happen in real system ?
The file ratio is big means that file lru list scanning is so big but
rotate is small.
It means file lru have few reclaimable page.

Isn't it ? I am confusing.
Could you elaborate, please if you don't mind ?

--
Kinds regards,
Minchan Kim
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