linux-kernel - Re: [BUGFIX][PATCH 1/4] memcg: fix limit estimation at reclaim for hugepage

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Date:	Fri, 28 Jan 2011 13:49:02 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hannes@...xchg.org" <hannes@...xchg.org>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>
Subject: Re: [BUGFIX][PATCH 1/4] memcg: fix limit estimation at reclaim for
 hugepage

On Fri, 28 Jan 2011 13:40:19 +0900
Daisuke Nishimura <nishimura@....nes.nec.co.jp> wrote:

> On Fri, 28 Jan 2011 12:24:49 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> 
> > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > 
> > Current memory cgroup's code tends to assume page_size == PAGE_SIZE
> > and arrangement for THP is not enough yet.
> > 
> > This is one of fixes for supporing THP. This adds
> > mem_cgroup_check_margin() and checks whether there are required amount of
> > free resource after memory reclaim. By this, THP page allocation
> > can know whether it really succeeded or not and avoid infinite-loop
> > and hangup.
> > 
> > Total fixes for do_charge()/reclaim memory will follow this patch.
> > 
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> 
> This patch looks good to me, but some nitpicks.
> 
> > ---
> >  include/linux/res_counter.h |   11 +++++++++++
> >  mm/memcontrol.c             |   25 ++++++++++++++++++++++++-
> >  2 files changed, 35 insertions(+), 1 deletion(-)
> > 
> > Index: mmotm-0125/include/linux/res_counter.h
> > ===================================================================
> > --- mmotm-0125.orig/include/linux/res_counter.h
> > +++ mmotm-0125/include/linux/res_counter.h
> > @@ -182,6 +182,17 @@ static inline bool res_counter_check_und
> >  	return ret;
> >  }
> >  
> > +static inline s64 res_counter_check_margin(struct res_counter *cnt)
> > +{
> > +	s64 ret;
> > +	unsigned long flags;
> > +
> > +	spin_lock_irqsave(&cnt->lock, flags);
> > +	ret = cnt->limit - cnt->usage;
> > +	spin_unlock_irqrestore(&cnt->lock, flags);
> > +	return ret;
> > +}
> > +
> >  static inline bool res_counter_check_under_soft_limit(struct res_counter *cnt)
> >  {
> >  	bool ret;
> > Index: mmotm-0125/mm/memcontrol.c
> > ===================================================================
> > --- mmotm-0125.orig/mm/memcontrol.c
> > +++ mmotm-0125/mm/memcontrol.c
> > @@ -1111,6 +1111,22 @@ static bool mem_cgroup_check_under_limit
> >  	return false;
> >  }
> >  
> > +static s64  mem_cgroup_check_margin(struct mem_cgroup *mem)
> > +{
> > +	s64 mem_margin;
> > +
> > +	if (do_swap_account) {
> > +		s64 memsw_margin;
> > +
> > +		mem_margin = res_counter_check_margin(&mem->res);
> > +		memsw_margin = res_counter_check_margin(&mem->memsw);
> > +		if (mem_margin > memsw_margin)
> > +			mem_margin = memsw_margin;
> > +	} else
> > +		mem_margin = res_counter_check_margin(&mem->res);
> > +	return mem_margin;
> > +}
> > +
> How about
> 
> 	mem_margin = res_counter_check_margin(&mem->res);
> 	if (do_swap_account)
> 		memsw_margin = res_counter_check_margin(&mem->memsw);
> 	else
> 		memsw_margin = RESOURCE_MAX;
> 
> 	return min(mem_margin, memsw_margin);
> 
> ?
> I think using min() makes it more clear what this function does.
> 

Ok.

> >  static unsigned int get_swappiness(struct mem_cgroup *memcg)
> >  {
> >  	struct cgroup *cgrp = memcg->css.cgroup;
> > @@ -1853,7 +1869,14 @@ static int __mem_cgroup_do_charge(struct
> >  	 * Check the limit again to see if the reclaim reduced the
> >  	 * current usage of the cgroup before giving up
> >  	 */
> > -	if (ret || mem_cgroup_check_under_limit(mem_over_limit))
> > +	if (mem_cgroup_check_margin(mem_over_limit) >= csize)
> > +		return CHARGE_RETRY;
> > +
> > +	/*
> > + 	 * If the charge size is a PAGE_SIZE, it's not hopeless while
> > + 	 * we can reclaim a page.
> > + 	 */
> > +	if (csize == PAGE_SIZE && ret)
> >  		return CHARGE_RETRY;
> >  
> >  	/*
> > 
> checkpatch complains some whitespace warnings.
> 
will fix soon.

-Kame

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