Re: [RFC 0/3] Improve memory statistics for virtio balloon

[David Hildenbrand <david@redhat.com>]

On 15.04.24 10:41, zhenwei pi wrote:
> Hi,
> 
> When the guest runs under critial memory pressure, the guest becomss
> too slow, even sshd turns D state(uninterruptible) on memory
> allocation. We can't login this VM to do any work on trouble shooting.
> 
> Guest kernel log via virtual TTY(on host side) only provides a few
> necessary log after OOM. More detail memory statistics are required,
> then we can know explicit memory events and estimate the pressure.
> 
> I'm going to introduce several VM counters for virtio balloon:
> - oom-kill
> - alloc-stall
> - scan-async
> - scan-direct
> - reclaim-async
> - reclaim-direct

IIUC, we're only exposing events that are already getting provided via 
all_vm_events(), correct?

In that case, I don't really see a major issue. Some considerations:

(1) These new events are fairly Linux specific.

PSWPIN and friends are fairly generic, but HGTLB is also already fairly 
Linux specific already. OOM-kills don't really exist on Windows, for 
example. We'll have to be careful of properly describing what the 
semantics are.

(2) How should we handle if Linux ever stops supporting a certain event 
(e.g., major reclaim rework). I assume, simply return nothing like we 
currently would for VIRTIO_BALLOON_S_HTLB_PGALLOC without 
CONFIG_HUGETLB_PAGE.

-- 
Cheers,

David / dhildenb