[ovirt-devel] Memory stats in VDSM

[Michal Skrivanek]

> On 28 Aug 2017, at 13:37, Juan Hernández <jhernand at redhat.com> wrote:
> 
> On 08/28/2017 01:11 PM, Tomáš Golembiovský wrote:
>> Hi,
>> there is ongoing effort to change how VDSM collects information about
>> memory usage from guests. We used to use oVirt guest agent to get the
>> statistics about free memory, swap usage, etc. This is going to change
>> and we will use stats provided by VirtIO Balloon driver. [1] This should
>> not break MOM nor Engine (current or previous versions).
>> There is however small downside to this change. We will not be able to
>> fetch information about buffers and caches on Linux guests anymore
>> (mem_cached and mem_buffers in memoryStats). The corollary of this is
>> that free memory reported by Engine will also no longer include those
>> statistics and reported free memory will be really (only) free memory.
>> I now there will be mixed feelings about this and we would like to get
>> the information about buffers and caches back to the VDSM. Correctly via
>> balloon driver statistics. [2] This effort will however take some time.
>>     Tomas
>> [1] https://gerrit.ovirt.org/#/q/topic:memory-stats
>> [2] https://lists.nongnu.org/archive/html/qemu-devel/2017-08/msg05239.html
> 
> Note that this information is currently reported by the engine REST API, so it is part of its contract. Removing it breaks backwards compatibility and causes a regression in this RFE:

we can either declare it deprecated or temporarily report 0 until the support propagates into qemu-ga

I think best way forward is to just make it optionally available when ovirt-guest-agent reports it.
I.e. users will get only part of the information when they run only qemu-ga, and that’s fine…

> 
>  [RFE] Report guests Buffered/Cached memory
>  https://bugzilla.redhat.com/1024010
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