Message-ID: <4919D370.7080301@redhat.com>
Date: Tue, 11 Nov 2008 20:48:16 +0200
From: Avi Kivity <avi@redhat.com>
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To: Andrew Morton <akpm@linux-foundation.org>
CC: Izik Eidus <ieidus@redhat.com>, linux-kernel@vger.kernel.org,
       linux-mm@kvack.org, kvm@vger.kernel.org, aarcange@redhat.com,
       chrisw@redhat.com
Subject: Re: [PATCH 0/4] ksm - dynamic page sharing driver for linux
References: <1226409701-14831-1-git-send-email-ieidus@redhat.com> <20081111103051.979aea57.akpm@linux-foundation.org>
In-Reply-To: <20081111103051.979aea57.akpm@linux-foundation.org>
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Andrew Morton wrote:
> The whole approach seems wrong to me.  The kernel lost track of these
> pages and then we run around post-facto trying to fix that up again. 
> Please explain (for the changelog) why the kernel cannot get this right
> via the usual sharing, refcounting and COWing approaches.
>   

For kvm, the kernel never knew those pages were shared.  They are loaded 
from independent (possibly compressed and encrypted) disk images.  These 
images are different; but some pages happen to be the same because they 
came from the same installation media.

For OpenVZ the situation is less clear, but if you allow users to 
independently upgrade their chroots you will eventually arrive at the 
same scenario (unless of course you apply the same merging strategy at 
the filesystem level).

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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