linux-kernel - Re: [patch 7/7] mm: reduce rmap overhead for ex-KSM page copies created on swap faults

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Date:	Wed, 19 Dec 2012 12:58:11 -0500
From:	Johannes Weiner <hannes@...xchg.org>
To:	Simon Jeons <simon.jeons@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Michal Hocko <mhocko@...e.cz>, Mel Gorman <mgorman@...e.de>,
	Hugh Dickins <hughd@...gle.com>,
	Satoru Moriya <satoru.moriya@....com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 7/7] mm: reduce rmap overhead for ex-KSM page copies
 created on swap faults

On Wed, Dec 19, 2012 at 02:01:19AM -0500, Simon Jeons wrote:
> On Mon, 2012-12-17 at 13:12 -0500, Johannes Weiner wrote:
> > When ex-KSM pages are faulted from swap cache, the fault handler is
> > not capable of re-establishing anon_vma-spanning KSM pages.  In this
> > case, a copy of the page is created instead, just like during a COW
> > break.
> > 
> > These freshly made copies are known to be exclusive to the faulting
> > VMA and there is no reason to go look for this page in parent and
> > sibling processes during rmap operations.
> > 
> > Use page_add_new_anon_rmap() for these copies.  This also puts them on
> > the proper LRU lists and marks them SwapBacked, so we can get rid of
> > doing this ad-hoc in the KSM copy code.
> 
> Is it just a code cleanup instead of reduce rmap overhead?

Both.
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