Re: [RFC] [PATCH 1/7 v2] memcg: remove unnecessary check in mem_cgroup_update_page_stat()

[Ying Han <yinghan@google.com>]

On Wed, Jan 18, 2012 at 5:01 AM, Michal Hocko <mhocko@suse.cz> wrote:
> On Wed 18-01-12 08:55:58, KAMEZAWA Hiroyuki wrote:
>> On Tue, 17 Jan 2012 16:16:20 +0100
>> Michal Hocko <mhocko@suse.cz> wrote:
>>
>> > On Fri 13-01-12 17:32:27, KAMEZAWA Hiroyuki wrote:
>> > >
>> > > From 788aebf15f3fa37940e0745cab72547e20683bf2 Mon Sep 17 00:00:00 2001
>> > > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>> > > Date: Thu, 12 Jan 2012 16:08:33 +0900
>> > > Subject: [PATCH 1/7] memcg: remove unnecessary check in mem_cgroup_update_page_stat()
>> > >
>> > > commit 10ea69f1182b removes move_lock_page_cgroup() in thp-split path.
>> > > So, this PageTransHuge() check is unnecessary, too.
>> >
>> > I do not see commit like that in the tree. I guess you meant
>> > memcg: make mem_cgroup_split_huge_fixup() more efficient which is not
>> > merged yet, right?
>> >
>>
>> This commit in the linux-next.
>
> Referring to commits from linux-next is tricky as it changes all the
> time. I guess that the full commit subject should be sufficient.
>
>> > > Note:
>> > >  - considering when mem_cgroup_update_page_stat() is called,
>> > >    there will be no race between split_huge_page() and update_page_stat().
>> > >    All required locks are held in higher level.
>> >
>> > We should never have THP page in this path in the first place. So why
>> > not changing this to VM_BUG_ON(PageTransHuge).
>> >
>>
>> Ying Han considers to support mlock stat.
>
> OK, got it. What about the following updated changelog instead?
>
> ===
> We do not have to check PageTransHuge in mem_cgroup_update_page_stat
> and fallback into the locked accounting because both move charge and thp

one nitpick. Should it be "move account" instead of "move charge"?

--Ying

> split up are done with compound_lock so they cannot race. update vs.
> move is protected by the mem_cgroup_stealed sufficiently.
>
> PageTransHuge pages shouldn't appear in this code path currently because
> we are tracking only file pages at the moment but later we are planning
> to track also other pages (e.g. mlocked ones).
> ===
>
>>
>> Thanks,
>> -Kame
>>
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>
> --
> Michal Hocko
> SUSE Labs
> SUSE LINUX s.r.o.
> Lihovarska 1060/12
> 190 00 Praha 9
> Czech Republic

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