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

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Date:	Tue,  1 Dec 2009 18:46:06 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Izik Eidus <ieidus@...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

> On Tue, Dec 01, 2009 at 06:28:16PM +0900, KOSAKI Motohiro wrote:
> > This patch doesn't works correctly. shrink_active_list() use page_referenced() for
> > clear young bit and doesn't use return value.
> 
> The whole point is that it's inefficient to clear all young bits just
> to move it to inactive list in the hope that new young bits will be
> set right before the page reaches the end of the inactive list.
> 
> > after this patch apply, shrink_active_list() move the page to inactive list although
> > the page still have many young bit. then, next shrink_inactive_list() move the page
> > to active list again.
> 
> yes it's not the end of the world, this only alter behavior for pages
> that have plenty of mappings. However I still it's inefficient to
> pretend to clear all young bits at once when page is deactivated. But
> this is not something I'm interested to argue about... let do what you
> like there, but as long as you pretend to clear all dirty bits there
> is no way we can fix anything. Plus we should touch ptes only in
> presence of heavy memory pressure, with light memory pressure ptes
> should _never_ be touched, and we should only shrink unmapped
> cache. And active/inactive movements must still happen even in
> presence of light memory pressure. The reason is that with light
> memory pressure we're not I/O bound and we don't want to waste time
> there. My patch is ok, what is not ok is the rest, you got to change
> the rest to deal with this.

Ah, well. please wait a bit. I'm under reviewing Larry's patch. I don't
dislike your idea. last mail only pointed out implementation thing.


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