Re: [PATCH] memcg: unlock page before charging it. (WasRe: [PATCHV2] mm: Do not keep page locked during page fault while charging it formemcg

From: Michal Hocko
Date: Thu Jun 23 2011 - 05:02:14 EST

On Thu 23-06-11 17:08:11, KAMEZAWA Hiroyuki wrote:
> On Thu, 23 Jun 2011 09:41:33 +0200
> Michal Hocko <mhocko@xxxxxxx> wrote:
> > Other than that:
> > Reviewed-by: Michal Hocko <mhocko@xxxxxxx>
> >
> I found the page is added to LRU before charging. (In this case,
> memcg's LRU is ignored.) I'll post a new version with a fix.

Yes, you are right. I have missed that.
This means that we might race with reclaim which could evict the COWed
page wich in turn would uncharge that page even though we haven't
charged it yet.

Can we postpone page_add_new_anon_rmap to the charging path or it would
just race somewhere else?

Michal Hocko
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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