linux-kernel - Re: [PATCH v7 1/2] KSM: numa awareness sysfs knob

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Message-ID: <1357609227.4105.3.camel@kernel.cn.ibm.com>
Date:	Mon, 07 Jan 2013 19:40:27 -0600
From:	Simon Jeons <simon.jeons@...il.com>
To:	Petr Holasek <pholasek@...hat.com>
Cc:	Hugh Dickins <hughd@...gle.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Izik Eidus <izik.eidus@...ellosystems.com>,
	Rik van Riel <riel@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Anton Arapov <anton@...hat.com>
Subject: Re: [PATCH v7 1/2] KSM: numa awareness sysfs knob

On Thu, 2013-01-03 at 13:24 +0100, Petr Holasek wrote:
> Hi Simon,
> 
> On Mon, 31 Dec 2012, Simon Jeons wrote:
> > On Fri, 2012-12-28 at 02:32 +0100, Petr Holasek wrote:
> > > 
> > > v7:	- added sysfs ABI documentation for KSM
> > 
> > Hi Petr,
> > 
> > How you handle "memory corruption because the ksm page still points to
> > the stable_node that has been freed" mentioned by Andrea this time?
> > 
> 

Hi Petr,

You still didn't answer my question mentioned above. :)

> <snip>
> 
> > >  
> > > +		/*
> > > +		 * If tree_page has been migrated to another NUMA node, it
> > > +		 * will be flushed out and put into the right unstable tree
> > > +		 * next time: only merge with it if merge_across_nodes.
> > 
> > Why? Do you mean swap based migration? Or where I miss ....?
> > 
> 
> It can be physical page migration triggered by page compaction, memory hotplug
> or some NUMA sched/memory balancing algorithm developed recently.
> 
> > > +		 * Just notice, we don't have similar problem for PageKsm
> > > +		 * because their migration is disabled now. (62b61f611e)
> > > +		 */
> 
> Migration of KSM pages is disabled now, you can look into ^^^ commit and
> changes introduced to migrate.c.
> 
> > > +		if (!ksm_merge_across_nodes && page_to_nid(tree_page) != nid) {
> > > +			put_page(tree_page);
> > > +			return NULL;
> > > +		}
> > > +
> > >  		ret = memcmp_pages(page, tree_page);
> 
> </snip>


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