linux-kernel - Re: [PATCH 2/6] ksm: dont allow overlap memory addresses registrations.

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Message-ID: <20090506140904.GY16078@random.random>
Date:	Wed, 6 May 2009 16:09:04 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	Rik van Riel <riel@...hat.com>, Izik Eidus <ieidus@...hat.com>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	chrisw@...hat.com, alan@...rguk.ukuu.org.uk, device@...ana.org,
	linux-mm@...ck.org, nickpiggin@...oo.com.au
Subject: Re: [PATCH 2/6] ksm: dont allow overlap memory addresses
	registrations.

On Wed, May 06, 2009 at 02:28:33PM +0100, Hugh Dickins wrote:
> There may prove to be various reasons why it wouldn't work out in practice;
> but when thinking of swapping them, it is worth considering if those KSM
> pages can just be assigned to a tmpfs file, then leave the swapping to that.

Not sure if I understand but the vma handled by KSM is anonymous, how
can you assign those pages to a tmpfs file, the anon vma won't permit
that, all regular anon methods will be called for swapin etc... What I
mean is that some change in core VM looks required and I plan those to
be external-rmap kind, KSM agnostic. But perhaps we can reuse some
shmem code yes, I didn't think about that yet. Anyway I'd rather
discuss this later, this isn't the time yet. I'm quite optimistic that
to make KSM swap it won't be a big change. For now there's a limit on
the max number of ksm pages that can be allocated at any given time so
to avoid OOM conditions, like the swap-compress logic that limits the
swapdevice size to less than ram.
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