[Xen-devel] Memory leak in migration on Xen 4.4

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

Following on from IRC conversation regarding an issue similar to [0] (which
was reported by someone else).

I've implemented the missing hypercall support in valgrind, see attached
which applies to SVN r15732. This is migrating cleanly (i.e. no
"README_MISSING_SYSCALL_OR_IOCTL" spew) for me with the attached
suppression file which knocks out one known (benign) issue.

With this things appear pretty clean using the Jessie packages for
everything. Just a few k lost or remaining reachable at the end (see
attached logs).

I'm somewhat concerned by the restore log though, it contains:

==3670== HEAP SUMMARY:
==3670==ÂÂÂÂÂin use at exit: 3,288 bytes in 4 blocks
==3670==ÂÂÂtotal heap usage: 1,343 allocs, 1,339 frees, 542,238,933 bytes 
allocated

That's 517M allocated, which is approximately the size of my test VM. It's
not clear though if this is cumulative usage or maximum concurrent usage.

Trying with a domain with 3500M (which is the most I can manage for a live
migration on this host) I get:

==4521== HEAP SUMMARY:
==4521==ÂÂÂÂÂin use at exit: 15,240 bytes in 4 blocks
==4521==ÂÂÂtotal heap usage: 8,847 allocs, 8,843 frees, 3,698,460,199 bytes 
allocated

So it does seem to related to the domain size.

However my dom0 has 512M RAM and 2G of swap, so 3500 should be well into
swap if this was max concurrent memory use, but I'm not seeing it getting
much into swap at all i.e. when the migration is about 80% done:

root@st40:~# free
ÂÂÂÂÂÂÂÂÂÂÂÂÂtotalÂÂÂÂÂÂÂusedÂÂÂÂÂÂÂfreeÂÂÂÂÂsharedÂÂÂÂbuffersÂÂÂÂÂcached
Mem:ÂÂÂÂÂÂÂÂ431092ÂÂÂÂÂ411448ÂÂÂÂÂÂ19644ÂÂÂÂÂÂÂÂ408ÂÂÂÂÂÂÂ4488ÂÂÂÂÂ198944
-/+ buffers/cache:ÂÂÂÂÂ208016ÂÂÂÂÂ223076
Swap:ÂÂÂÂÂÂ1949692ÂÂÂÂÂÂÂ1036ÂÂÂÂ1948656

So I conclude that the "bytes allocated" is cumulative and not maximum
concurrent (and that I can still not reproduce this issue).

For completeness I've attached my libxl-save-helper wrapper script.

I'm running everything from the Jessie packages.

Ian.

[0]Âhttps://bugs.debian.org/cgi-bin/bugreport.cgi?bug=797205

Attachment: 0001-xen-Implement-__HYPERVISOR_mmu_update.patch
Description: Text Data

Attachment: xen-migration.supp
Description: Text document

Attachment: libxl-save-helper--restore-domain.valgrind.log
Description: Text Data

Attachment: libxl-save-helper--save-domain.valgrind.log
Description: Text Data

Attachment: libxl-save-helper
Description: application/shellscript

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