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[Xen-devel] Could the page sharing inside domain? (memory_sharing on xen

To: "'Keir Fraser'" <Keir.Fraser@xxxxxxxxxxxxx>
Subject: [Xen-devel] Could the page sharing inside domain? (memory_sharing on xen)
From: "xiaoyun.maoxy" <xiaoyun.maoxy@xxxxxxxxxxxxxx>
Date: Wed, 5 Jan 2011 21:11:50 +0800
Cc: 'tinnycloud' <tinnycloud@xxxxxxxxxxx>, 'James Harper' <james.harper@xxxxxxxxxxxxxxxx>, JBeulich@xxxxxxxxxx, 'Paul Durrant' <Paul.Durrant@xxxxxxxxxx>, 'Steven Smith' <Steven.Smith@xxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
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Hi Keir:

        One of the features listed as having been added to Xen 4 is page
sharing for HVM domUs. 
Pity is it has been disabled since buggy. Well I tried to make it work these

        After go through the code and get thoroughly concept of page
sharing, I've
been able to setup test environment, but confronted domU crash.

        One abnormal output from serial is 

(XEN) mm.c:859:d0 Error getting mfn 2df15f (pfn fffffffffffffffe) from L1
entry 80000002df15f627 for l1e_owner=0, pg_owner=4
(XEN) mm.c:859:d0 Error getting mfn 2df160 (pfn fffffffffffffffe) from L1
entry 80000002df160627 for l1e_owner=0, pg_owner=4

        Later, I found this is related to page sharing inside domain itself.

        That is when a domain X first read IO sectors Y, it will nominate
the gref into xen(that is build a hash entry in xen)
        , after IO completion, it will build a hash entry in tapdisk2 hash
        But later domain X read same sectors again, it can find entry in
both hash tables, and page sharing works, one page freed.
 Then I can see above serial output.

        So my question is: Is page sharing legal inside domain?



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