Re: [Xen-devel] xenstored memory leak

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 13/07/16 13:21, Juergen Gross wrote:
> On 06/07/16 09:31, Juergen Gross wrote:
>> While testing some patches for support of ballooning in Mini-OS by using
>> the xenstore domain I realized that each xl create/destroy pair would
>> increase memory consumption in Mini-OS by about 5kB. Wondering whether
>> this is a xenstore domain only effect I did the same test with xenstored
>> and oxenstored daemons.
>>
>> xenstored showed the same behavior, the "referenced" size showed by the
>> pmap command grew by about 5kB for each create/destroy pair.
>>
>> oxenstored seemed to be even worse in the beginning (about 6kB for each
>> pair), but after about 100 create/destroys the value seemed to be
>> rather stable.
>>
>> Did anyone notice this memory leak before?
> I think I've found the problem:
>
> qemu as the device model is setting up a xenstore watch for each backend
> type it is supporting. Unfortunately those watches are never removed
> again. This sums up to the observed memory leak.
>
> I'm not sure how oxenstored is avoiding the problem, may be by testing
> socket connections to be still alive and so detecting qemu has gone.
> OTOH this won't help for oxenstored running in another domain than the
> device model (either due to oxenstore-stubdom, or a driver domain with
> a qemu based device model).

I do seem to remember something along those lines.

>
> I'll post a qemu patch to remove those watches on exit soon.

That is good, but there needs to be further consideration as to how to
clean up after a crashed qemu/etc.

>
> To find the problem I've added some debug aid to xenstored: when
> a special parameter is specified on invocation it will dump its memory
> allocation structure via talloc_report_full() to a file whenever it is
> receiving a SIGUSR1 signal. Anybody interested in this patch?

Sounds useful.  +1

~Andrew

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