Messages in this thread | | | Date | Tue, 11 Nov 2008 21:18:23 +0200 | From | Izik Eidus <> | Subject | Re: [PATCH 0/4] ksm - dynamic page sharing driver for linux |
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Andrew Morton wrote: > 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 ;) ] KSM is separate driver , it doesn't change anything in the VM but adding two helper functions.
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