linux-kernel - Re: [PATCH 4/4] Memory controller soft limit reclaim on contention (v3)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue,  3 Mar 2009 11:43:49 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	kosaki.motohiro@...fujitsu.com, linux-mm@...ck.org,
	Sudhir Kumar <skumar@...ux.vnet.ibm.com>,
	YAMAMOTO Takashi <yamamoto@...inux.co.jp>,
	Bharata B Rao <bharata@...ibm.com>,
	Paul Menage <menage@...gle.com>, lizf@...fujitsu.com,
	linux-kernel@...r.kernel.org, David Rientjes <rientjes@...gle.com>,
	Pavel Emelianov <xemul@...nvz.org>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH 4/4] Memory controller soft limit reclaim on contention (v3)

> * KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> [2009-03-02 12:08:01]:
> 
> > Hi Balbir,
> > 
> > > @@ -2015,9 +2016,12 @@ static int kswapd(void *p)
> > >  		finish_wait(&pgdat->kswapd_wait, &wait);
> > >  
> > >  		if (!try_to_freeze()) {
> > > +			struct zonelist *zl = pgdat->node_zonelists;
> > >  			/* We can speed up thawing tasks if we don't call
> > >  			 * balance_pgdat after returning from the refrigerator
> > >  			 */
> > > +			if (!order)
> > > +				mem_cgroup_soft_limit_reclaim(zl, GFP_KERNEL);
> > >  			balance_pgdat(pgdat, order);
> > >  		}
> > >  	}
> > 
> > kswapd's roll is increasing free pages until zone->pages_high in "own node".
> > mem_cgroup_soft_limit_reclaim() free one (or more) exceed page in any node.
> > 
> > Oh, well.
> > I think it is not consistency.
> > 
> > if mem_cgroup_soft_limit_reclaim() is aware to target node and its pages_high,
> > I'm glad.
> 
> Yes, correct the role of kswapd is to keep increasing free pages until
> zone->pages_high and the first set of pages to consider is the memory
> controller over their soft limits. We pass the zonelist to ensure that
> while doing soft reclaim, we focus on the zonelist associated with the
> node. Kamezawa had concernes over calling the soft limit reclaim from
> __alloc_pages_internal(), did you prefer that call path? 

I read your patch again.
So, mem_cgroup_soft_limit_reclaim() caller place seems in balance_pgdat() is better.

Please imazine most bad scenario.
CPU0 (kswapd) take to continue shrinking.
CPU1 take another activity and charge memcg conteniously.
At that time, balance_pgdat() don't exit very long time. then 
mem_cgroup_soft_limit_reclaim() is never called.

In ideal, if another cpu take another charge, kswapd should shrink 
soft limit again.


btw, I don't like "if (!order)" condition. memcg soft limit sould be
always shrinked although 
it's the order of because wakeup_kswapd() argument is merely hint.

another process want another order.



--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/