Re: [ovirt-devel] Memory stats in VDSM

On 28 Aug 2017, at 14:02, Juan Hernández <jhernand(a)redhat.com&gt; wrote: On 08/28/2017 01:57 PM, Juan Hernández wrote: > On 08/28/2017 01:42 PM, Michal Skrivanek wrote: >> >>> On 28 Aug 2017, at 13:37, Juan Hernández <jhernand(a)redhat.com&gt; 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 >> > So there will be an interval of time where it will not be reported? Will that affect released versions of the system or it is just something that we will re-add before the next release? It is released versions of the system that I am concerned about. We should not do a release that breaks backwards compatibility. It is completely OK if we break it in between releases. >> 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… >> Not sure I understand this. Currently, if I understand correctly, these values are only populated if the ovirt-guest-agent is installed? That is OK (may be worth documenting it). We plan to replace ovirt-guest-agent with qemu-ga in a mandatory way? Or will the user be able to use one or the other?

If the user decides to use the ovirt-guest-agent, will we continue to report these statistics?

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