linux-kernel - Re: [PATCH 3/7] memcg : fix mem_cgroup_check_under

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Message-Id: <20110124190359.a79deec8.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Mon, 24 Jan 2011 19:03:59 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [PATCH 3/7] memcg : fix mem_cgroup_check_under_limit

On Mon, 24 Jan 2011 11:04:34 +0100
Johannes Weiner <hannes@...xchg.org> wrote:
  
> >  	ret = mem_cgroup_hierarchical_reclaim(mem_over_limit, NULL,
> > -					gfp_mask, flags);
> > +					gfp_mask, flags, csize);
> >  	/*
> >  	 * try_to_free_mem_cgroup_pages() might not give us a full
> >  	 * picture of reclaim. Some pages are reclaimed and might be
> > @@ -1852,7 +1853,7 @@ 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 (ret || mem_cgroup_check_under_limit(mem_over_limit, csize))
> >  		return CHARGE_RETRY;
> 
> This is the only site that is really involved with THP. 

yes.

> But you need to touch every site because you change mem_cgroup_check_under_limit()
> instead of adding a new function.
> 
Yes.

> I would suggest just adding another function for checking available
> space explicitely and only changing this single call site to use it.
> 
> Just ignore the return value of mem_cgroup_hierarchical_reclaim() and
> check for enough space unconditionally.
> 
> Everybody else is happy with PAGE_SIZE pages.
> 
Hmm. ok, let us changes to be small and see how often hugepage alloc will fail.

Thanks,
-Kame



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