linux-kernel - Re: [PATCH] mm: inactive-clean list

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Message-ID: <6e0cfd1d0607260604w3e8636e4taaea4bc918397b34@mail.gmail.com>
Date:	Wed, 26 Jul 2006 15:04:05 +0200
From:	"Martin Schwidefsky" <schwidefsky@...glemail.com>
To:	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>
Cc:	"Rik van Riel" <riel@...hat.com>, linux-mm <linux-mm@...ck.org>,
	"Linus Torvalds" <torvalds@...l.org>,
	"Andrew Morton" <akpm@...l.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: inactive-clean list

On 7/26/06, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> > Hmm, I wonder how the inactive clean list helps in regard to the fast
> > host reclaim
> > scheme. In particular since the memory pressure that triggers the
> > reclaim is in the
> > host, not in the guest. So all pages might be on the active list but
> > the host still
> > wants to be able to discard pages.
> >
>
> I think Rik would want to set all the already unmapped pages to volatile
> state in the hypervisor.
>
> These pages can be dropped without loss of information on the guest
> system since they are all already on a backing-store, be it regular
> files or swap.

I guessed that as well. It isn't good enough. Consider a guest with a
large (virtual) memory size and a host with a small physical memory
size. The guest will never put any page on the inactive_clean list
because it does not have memory pressure. vmscan will never run. The
host wants to reclaim memory of the guest, but since the
inactive_clean list is empty it will find only stable pages.

-- 
blue skies,
  Martin
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