From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 11 Nov 2008 11:11:10 -0800 From: Andrew Morton Subject: Re: [PATCH 0/4] ksm - dynamic page sharing driver for linux Message-Id: <20081111111110.decc0f06.akpm@linux-foundation.org> In-Reply-To: <4919D370.7080301@redhat.com> References: <1226409701-14831-1-git-send-email-ieidus@redhat.com> <20081111103051.979aea57.akpm@linux-foundation.org> <4919D370.7080301@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Avi Kivity Cc: ieidus@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kvm@vger.kernel.org, aarcange@redhat.com, chrisw@redhat.com List-ID: On Tue, 11 Nov 2008 20:48:16 +0200 Avi Kivity wrote: > 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. What userspace-only changes could fix this? Identify the common data, write it to a flat file and mmap it, something like that? > 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). hm. There has been the occasional discussion about idenfifying all-zeroes pages and scavenging them, repointing them at the zero page. Could this infrastructure be used for that? (And how much would we gain from it?) [I'm looking for reasons why this is more than a muck-up-the-vm-for-kvm thing here ;) ] -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org