Messages in this thread | | | Date | Mon, 12 Mar 2007 22:04:39 -0800 | From | Andrew Morton <> | Subject | Re: [RFC][PATCH 2/7] RSS controller core |
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> On Mon, 12 Mar 2007 23:41:29 +0100 Herbert Poetzl <herbert@13thfloor.at> wrote: > On Mon, Mar 12, 2007 at 11:42:59AM -0700, Dave Hansen wrote: > > How about we drill down on these a bit more. > > > > On Mon, 2007-03-12 at 02:00 +0100, Herbert Poetzl wrote: > > > - shared mappings of 'shared' files (binaries > > > and libraries) to allow for reduced memory > > > footprint when N identical guests are running > > > > So, it sounds like this can be phrased as a requirement like: > > > > "Guests must be able to share pages." > > > > Can you give us an idea why this is so? > > sure, one reason for this is that guests tend to > be similar (or almost identical) which results > in quite a lot of 'shared' libraries and executables > which would otherwise get cached for each guest and > would also be mapped for each guest separately
nooooooo. What you're saying there amounts to text replication. There is no proposal here to create duplicated copies of pagecache pages: the VM just doesn't support that (Nick has soe protopatches which do this as a possible NUMA optimisation).
So these mmapped pages will contiue to be shared across all guests. The problem boils down to "which guest(s) get charged for each shared page".
A simple and obvious and easy-to-implement answer is "the guest which paged it in". I think we should firstly explain why that is insufficient.
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