From: Michal Hocko <mhocko@suse.cz>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Christoph Hellwig <hch@infradead.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Hugh Dickins <hughd@google.com>, Rik van Riel <riel@redhat.com>,
Michel Lespinasse <walken@google.com>,
Mel Gorman <mgorman@suse.de>, Lutz Vieweg <lvml@5t9.de>
Subject: Re: [PATCH] mm: preallocate page before lock_page at filemap COW. (WasRe: [PATCH V2] mm: Do not keep page locked during page fault while charging it for memcg
Date: Thu, 23 Jun 2011 13:58:55 +0200 [thread overview]
Message-ID: <20110623115855.GF31593@tiehlicka.suse.cz> (raw)
In-Reply-To: <20110623190157.1bc8cbb9.kamezawa.hiroyu@jp.fujitsu.com>
On Thu 23-06-11 19:01:57, KAMEZAWA Hiroyuki wrote:
> On Thu, 23 Jun 2011 11:02:04 +0200
> Michal Hocko <mhocko@suse.cz> wrote:
>
> > On Thu 23-06-11 17:08:11, KAMEZAWA Hiroyuki wrote:
> > > On Thu, 23 Jun 2011 09:41:33 +0200
> > > Michal Hocko <mhocko@suse.cz> wrote:
> > [...]
> > > > Other than that:
> > > > Reviewed-by: Michal Hocko <mhocko@suse.cz>
> > > >
> > >
> > > 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?
> >
>
> I got a different idea. How about this ?
> I think this will have benefit for non-memcg users under OOM, too.
Could you be more specific? I do not see how preallocation which might
turn out to be pointless could help under OOM.
>
> A concerns is VM_FAULT_RETRY case but wait-for-lock will be much heavier
> than preallocation + free-for-retry cost.
Preallocation is rather costly when fault handler fails (e.g. SIGBUS
which is the easiest one to trigger).
I am not saying this approach is bad but I think that preallocation can
be much more costly than unlock, charge and lock&recheck approach.
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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next prev parent reply other threads:[~2011-06-23 11:58 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-22 12:06 [PATCH] " Michal Hocko
2011-06-22 12:15 ` Christoph Hellwig
2011-06-22 12:32 ` [PATCH V2] " Michal Hocko
2011-06-23 6:08 ` [PATCH] memcg: unlock page before charging it. (WasRe: " KAMEZAWA Hiroyuki
2011-06-23 7:23 ` Daisuke Nishimura
2011-06-23 7:41 ` Michal Hocko
2011-06-23 8:08 ` KAMEZAWA Hiroyuki
2011-06-23 9:02 ` Michal Hocko
2011-06-23 10:01 ` [PATCH] mm: preallocate page before lock_page at filemap COW. " KAMEZAWA Hiroyuki
2011-06-23 11:58 ` Michal Hocko [this message]
2011-06-23 13:01 ` Hiroyuki Kamezawa
2011-06-23 13:23 ` Michal Hocko
2011-06-23 13:51 ` Hiroyuki Kamezawa
2011-06-24 7:57 ` Michal Hocko
2011-06-24 11:46 ` Hiroyuki Kamezawa
2011-07-12 9:48 ` Michal Hocko
2012-01-26 10:46 ` Lutz Vieweg
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