linux-kernel - Re: [PATCH -mm] memcg: fix handling of shmem migration(v2)

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Message-Id: <20080918110353.2c8d0602.nishimura@mxp.nes.nec.co.jp>
Date:	Thu, 18 Sep 2008 11:03:53 +0900
From:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	nishimura@....nes.nec.co.jp, kamezawa.hiroyu@...fujitsu.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	balbir@...ux.vnet.ibm.com, xemul@...nvz.org
Subject: Re: [PATCH -mm] memcg: fix handling of shmem migration(v2)

On Wed, 17 Sep 2008 15:51:12 -0700, Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Wed, 17 Sep 2008 16:55:44 +0900
> Daisuke Nishimura <nishimura@....nes.nec.co.jp> wrote:
> 
> > Before this patch, if migrating shmem/tmpfs pages, newpage would be
> > charged with PAGE_CGROUP_FLAG_FILE set, while oldpage has been charged
> > without the flag.
> > 
> > The problem here is mem_cgroup_move_lists doesn't clear(or set)
> > the PAGE_CGROUP_FLAG_FILE flag, so pc->flags of the newpage
> > remains PAGE_CGROUP_FLAG_FILE set even when the pc is moved to
> > another lru(anon) by mem_cgroup_move_lists. And this leads to
> > incorrect MEM_CGROUP_ZSTAT.
> > (In my test, I see an underflow of MEM_CGROUP_ZSTAT(active_file).
> > As a result, mem_cgroup_calc_reclaim returns very huge number and
> > causes soft lockup on page reclaim.)
> > 
> > I'm not sure if mem_cgroup_move_lists should handle PAGE_CGROUP_FLAG_FILE
> > or not(I suppose it should be used to move between active <-> inactive,
> > not anon <-> file), I added MEM_CGROUP_CHARGE_TYPE_SHMEM for precharge
> > at shmem's page migration.
> > 
> > 
> > ChangeLog: v1->v2
> > - instead of modifying migrate.c, modify memcontrol.c only.
> > - add MEM_CGROUP_CHARGE_TYPE_SHMEM.
> > 
> > 
> > Signed-off-by: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
> > ---
> >  mm/memcontrol.c |   13 ++++++++++---
> >  1 files changed, 10 insertions(+), 3 deletions(-)
> > 
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 2979d22..ef8812d 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -179,6 +179,7 @@ enum charge_type {
> >  	MEM_CGROUP_CHARGE_TYPE_CACHE = 0,
> >  	MEM_CGROUP_CHARGE_TYPE_MAPPED,
> >  	MEM_CGROUP_CHARGE_TYPE_FORCE,	/* used by force_empty */
> > +	MEM_CGROUP_CHARGE_TYPE_SHMEM,	/* used by page migration of shmem */
> >  };
> >  
> >  /*
> > @@ -579,8 +580,10 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
> >  			pc->flags |= PAGE_CGROUP_FLAG_FILE;
> >  		else
> >  			pc->flags |= PAGE_CGROUP_FLAG_ACTIVE;
> > -	} else
> > +	} else if (ctype == MEM_CGROUP_CHARGE_TYPE_MAPPED)
> >  		pc->flags = PAGE_CGROUP_FLAG_ACTIVE;
> > +	else /* MEM_CGROUP_CHARGE_TYPE_SHMEM */
> > +		pc->flags = PAGE_CGROUP_FLAG_CACHE | PAGE_CGROUP_FLAG_ACTIVE;
> >  
> >  	lock_page_cgroup(page);
> >  	if (unlikely(page_get_page_cgroup(page))) {
> > @@ -739,8 +742,12 @@ int mem_cgroup_prepare_migration(struct page *page, struct page *newpage)
> >  	if (pc) {
> >  		mem = pc->mem_cgroup;
> >  		css_get(&mem->css);
> > -		if (pc->flags & PAGE_CGROUP_FLAG_CACHE)
> > -			ctype = MEM_CGROUP_CHARGE_TYPE_CACHE;
> > +		if (pc->flags & PAGE_CGROUP_FLAG_CACHE) {
> > +			if (page_is_file_cache(page))
> > +				ctype = MEM_CGROUP_CHARGE_TYPE_CACHE;
> > +			else
> > +				ctype = MEM_CGROUP_CHARGE_TYPE_SHMEM;
> > +		}
> >  	}
> >  	unlock_page_cgroup(page);
> >  	if (mem) {
> 
> I queued this as a fix against
> vmscan-split-lru-lists-into-anon-file-sets.patch.  Was that appropriate?
> 
Yes, thanks.

> If the bug you're fixing here is also present in mainline then I'll
> need to ask for a tested patch against mainline, please.
> 
I don't think this bug exist in mainline, where memcg have
only two ZSTAT(active/inactive) and mem_cgroup_move_lists can handle
them properly.


Thanks,
Daisuke Nishimura.
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