linux-kernel - Re: [patch 1/4] mm: memcontrol: uncharge pages on swapout

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Message-ID: <20141021203907.GA29116@phnom.home.cmpxchg.org>
Date:	Tue, 21 Oct 2014 16:39:07 -0400
From:	Johannes Weiner <hannes@...xchg.org>
To:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>, Michal Hocko <mhocko@...e.cz>,
	Vladimir Davydov <vdavydov@...allels.com>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 1/4] mm: memcontrol: uncharge pages on swapout

On Tue, Oct 21, 2014 at 10:07:52AM +0900, Kamezawa Hiroyuki wrote:
> (2014/10/21 0:22), Johannes Weiner wrote:
> > mem_cgroup_swapout() is called with exclusive access to the page at
> > the end of the page's lifetime.  Instead of clearing the PCG_MEMSW
> > flag and deferring the uncharge, just do it right away.  This allows
> > follow-up patches to simplify the uncharge code.
> > 
> > Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> > ---
> >   mm/memcontrol.c | 17 +++++++++++++----
> >   1 file changed, 13 insertions(+), 4 deletions(-)
> > 
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index bea3fddb3372..7709f17347f3 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -5799,6 +5799,7 @@ static void __init enable_swap_cgroup(void)
> >    */
> >   void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
> >   {
> > +	struct mem_cgroup *memcg;
> >   	struct page_cgroup *pc;
> >   	unsigned short oldid;
> >   
> > @@ -5815,13 +5816,21 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
> >   		return;
> >   
> >   	VM_BUG_ON_PAGE(!(pc->flags & PCG_MEMSW), page);
> shouldn't be removed ?

It's still a legitimate check at this point.  But it's removed later
in the series when PCG_MEMSW itself goes away.

> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

Thanks!
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