Messages in this thread | | | Date | Tue, 11 Nov 2008 11:11:10 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH 0/4] ksm - dynamic page sharing driver for linux |
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On Tue, 11 Nov 2008 20:48:16 +0200 Avi Kivity <avi@redhat.com> 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 ;) ]
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