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

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Wed, 18 Jan 2012 14:01:02 +0100
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
> 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).
> ===

ok, will use this :) Thank you.

-Kame

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