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[Xen-devel] checkLiveMigrateMemory() insufficient?

I occassionally see failures live migrating due to running out of memory in
sh_set_allocation(). For example on a 4Gb machine with freely-balloonable dom0,
the routine attempts to allocate 1536 pages of heap, and fails right at the

(xVM) free 5dc total 5dc xenheap 21 total 40000 max 40000
(xVM) failed to allocate shadow pages from domheap

This is a 64-bit guest on 64-bit host. I see this in xend.log:

[2008-10-01 08:56:31 100921] DEBUG (XendDomainInfo:2121) overhead_kb is now 9216
[2008-10-01 08:56:31 100921] DEBUG (balloon:116) Balloon: 12216 KiB free; need 
9216; done.

(Note that I added an extra 1Mb on to the normal overhead_kb allocation).

So we have 12Mb free from physinfo, and we're trying to allocate 6Mb plus some
other smaller allocations. I suspect the issue is one of fragmentation of the
heap? That is, no allocations of order SHADOW_MAX_ORDER could be found?

Does the linux balloon handler free in page-sized increments like Solaris
currently does?

Is there a better way to handle this?


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