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

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Message-ID: <20130103122416.GB2277@thinkpad-work.redhat.com>
Date:	Thu, 3 Jan 2013 13:24:17 +0100
From:	Petr Holasek <pholasek@...hat.com>
To:	Simon Jeons <simon.jeons@...il.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

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?
> 

<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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