linux-kernel - Re: [RFC][PATCH 4/4] memcg: make oom less frequently

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Date:	Fri, 9 Jan 2009 18:37:04 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	lizf@...fujitsu.com, menage@...gle.com
Subject: Re: [RFC][PATCH 4/4] memcg: make oom less frequently

On Fri, 9 Jan 2009 14:33:43 +0530
Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:

> * Daisuke Nishimura <nishimura@....nes.nec.co.jp> [2009-01-09 17:52:15]:
> 
> > On Fri, 9 Jan 2009 11:28:04 +0530, Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> > > * Daisuke Nishimura <nishimura@....nes.nec.co.jp> [2009-01-08 19:15:20]:
> > > 
> > > > In previous implementation, mem_cgroup_try_charge checked the return
> > > > value of mem_cgroup_try_to_free_pages, and just retried if some pages
> > > > had been reclaimed.
> > > > But now, try_charge(and mem_cgroup_hierarchical_reclaim called from it)
> > > > only checks whether the usage is less than the limit.
> > > > 
> > > > This patch tries to change the behavior as before to cause oom less frequently.
> > > > 
> > > > To prevent try_charge from getting stuck in infinite loop,
> > > > MEM_CGROUP_RECLAIM_RETRIES_MAX is defined.
> > > > 
> > > > 
> > > > Signed-off-by: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
> > > > ---
> > > >  mm/memcontrol.c |   16 ++++++++++++----
> > > >  1 files changed, 12 insertions(+), 4 deletions(-)
> > > > 
> > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > > > index 804c054..fedd76b 100644
> > > > --- a/mm/memcontrol.c
> > > > +++ b/mm/memcontrol.c
> > > > @@ -42,6 +42,7 @@
> > > > 
> > > >  struct cgroup_subsys mem_cgroup_subsys __read_mostly;
> > > >  #define MEM_CGROUP_RECLAIM_RETRIES	5
> > > > +#define MEM_CGROUP_RECLAIM_RETRIES_MAX	32
> > > 
> > > Why 32 are you seeing frequent OOMs? I had 5 iterations to allow
> > > 
> > > 1. pages to move to swap cache, which added back pressure to memcg in
> > > the original implementation, since the pages came back
> > > 2. It look longer to move, recalim those pages.
> > > 
> > > Ideally 3 would suffice, but I added an additional 2 retries for
> > > safety.
> > > 
> > Before this patch, try_charge doesn't check the return value of
> > try_to_free_page, i.e. how many pages has been reclaimed, and
> > only checks whether the usage has become less than the limit.
> > So, oom can be caused if the group is too busy.
> > 
> > IIRC memory-cgroup-hierarchical-reclaim patch introduced this behavior,
> > and, I don't remember in detail, some tests which had not caused oom
> > started to cause oom after it.
> > That was the motivation of my first version of this patch(*1).
> > 
> > *1 http://lkml.org/lkml/2008/11/28/35
> > 
> > Anyway, this is the updated version.
> > I removed RETRIES_MAX.
> > 
> > 
> > Thanks,
> > Daisuke Nishimura.
> > ===
> > From: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
> > 
> > In previous implementation, mem_cgroup_try_charge checked the return
> > value of mem_cgroup_try_to_free_pages, and just retried if some pages
> > had been reclaimed.
> > But now, try_charge(and mem_cgroup_hierarchical_reclaim called from it)
> > only checks whether the usage is less than the limit.
> > 
> > This patch tries to change the behavior as before to cause oom less frequently.
> > 
> > ChangeLog: RFC->v1
> > - removed RETRIES_MAX.
> > 
> > 
> > Signed-off-by: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
> > ---
> >  mm/memcontrol.c |   10 ++++++----
> >  1 files changed, 6 insertions(+), 4 deletions(-)
> > 
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 7ba5c61..fb0e9eb 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -781,10 +781,10 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
> >  	 * but there might be left over accounting, even after children
> >  	 * have left.
> >  	 */
> > -	ret = try_to_free_mem_cgroup_pages(root_mem, gfp_mask, noswap,
> > +	ret += try_to_free_mem_cgroup_pages(root_mem, gfp_mask, noswap,
> >  					   get_swappiness(root_mem));
> >  	if (mem_cgroup_check_under_limit(root_mem))
> > -		return 0;
> > +		return 1;	/* indicate reclaim has succeeded */
> >  	if (!root_mem->use_hierarchy)
> >  		return ret;
> > 
> > @@ -795,10 +795,10 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
> >  			next_mem = mem_cgroup_get_next_node(root_mem);
> >  			continue;
> >  		}
> > -		ret = try_to_free_mem_cgroup_pages(next_mem, gfp_mask, noswap,
> > +		ret += try_to_free_mem_cgroup_pages(next_mem, gfp_mask, noswap,
> >  						   get_swappiness(next_mem));
> >  		if (mem_cgroup_check_under_limit(root_mem))
> > -			return 0;
> > +			return 1;	/* indicate reclaim has succeeded */
> >  		next_mem = mem_cgroup_get_next_node(root_mem);
> >  	}
> >  	return ret;
> > @@ -883,6 +883,8 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
> > 
> >  		ret = mem_cgroup_hierarchical_reclaim(mem_over_limit, gfp_mask,
> >  							noswap);
> > +		if (ret)
> > +			continue;
> > 
> >  		/*
> >  		 * try_to_free_mem_cgroup_pages() might not give us a full
> > 
> 
> This makes sense
> 
> Acked-by: Balbir Singh <balbir@...ux.vnet.ibm.com>
> 
me, too

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



> 
> -- 
> 	Balbir
> 

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