Date: Fri, 4 Dec 2009 14:16:17 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>, Rik van Riel <riel@redhat.com>,
       Hugh Dickins <hugh.dickins@tiscali.co.uk>,
       Andrew Morton <akpm@linux-foundation.org>,
       Izik Eidus <ieidus@redhat.com>, Chris Wright <chrisw@redhat.com>,
       linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 2/9] ksm: let shared pages be swappable
Message-Id: <20091204141617.f4c491e7.kamezawa.hiroyu@jp.fujitsu.com>
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On Fri,  4 Dec 2009 14:06:07 +0900 (JST)
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:

> > Umm?? Personally I don't like knob. If you have problematic workload,
> > please tell it us. I will try to make reproduce environment on my box.
> > If current code doesn't works on KVM or something-else, I really want
> > to fix it.
> > 
> > I think Larry's trylock idea and your 64 young bit idea can be combinate.
> > I only oppose the page move to inactive list without clear young bit. IOW,
> > if VM pressure is very low and the page have lots young bit, the page should
> > go back active list although trylock(ptelock) isn't contended.
> > 
> > But unfortunatelly I don't have problem workload as you mentioned. Anyway
> > we need evaluate way to your idea. We obviouslly more info.
> 
> [Off topic start]
> 
> Windows kernel have zero page thread and it clear the pages in free list
> periodically. because many windows subsystem prerefer zero filled page.
> hen, if we use windows guest, zero filled page have plenty mapcount rather
> than other typical sharing pages, I guess.
> 
> So, can we mark as unevictable to zero filled ksm page? 
> 

Hmm, can't we use ZERO_PAGE we have now ?
If do so,
 - no mapcount check
 - never on LRU
 - don't have to maintain shared information because ZERO_PAGE itself has
   copy-on-write nature.

Thanks,
-Kame

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