Messages in this thread | | | Date | Tue, 13 Mar 2007 13:19:53 +0300 | From | Kirill Korotaev <> | Subject | Re: [Devel] Re: [RFC][PATCH 2/7] RSS controller core |
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Andrew Morton 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. I guess by "paged it in" you essentially mean "mapped the page into address space for the *first* time"?
i.e. how many times the same page mapped into 2 address spaces in the same container should be accounted for?
We believe ONE. It is better due to: - it allows better estimate how much RAM container uses. - if one container mapped a single page 10,000 times, it doesn't mean it is worse than a container which mapped only 200 pages and that it should be killed in case of OOM.
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