linux-kernel - Re: [PATCH 2/9] ksm: let shared pages be swappable

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Message-Id: <20091201125801.5C16.A69D9226@jp.fujitsu.com>
Date:	Tue,  1 Dec 2009 13:14:20 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Hugh Dickins <hugh.dickins@...cali.co.uk>
Cc:	kosaki.motohiro@...fujitsu.com,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Izik Eidus <ieidus@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Chris Wright <chrisw@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 2/9] ksm: let shared pages be swappable

> > btw, I'm not sure why bellow kmem_cache_zalloc() is necessary. Why can't we
> > use stack?
> 
> Well, I didn't use stack: partly because I'm so ashamed of the pseudo-vmas
> on the stack in mm/shmem.c, which have put shmem_getpage() into reports
> of high stack users (I've unfinished patches to deal with that); and
> partly because page_referenced_ksm() and try_to_unmap_ksm() are on
> the page reclaim path, maybe way down deep on a very deep stack.
> 
> But it's not something you or I should be worrying about: as the comment
> says, this is just a temporary hack, to present a patch which gets KSM
> swapping working in an understandable way, while leaving some corrections
> and refinements to subsequent patches.  This pseudo-vma is removed in the
> very next patch.

I see. thanks for kindly explanation :)



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