Re: On guest free page hinting and OOM

From: David Hildenbrand
Date: Tue Apr 02 2019 - 16:33:11 EST

On 02.04.19 21:49, Michael S. Tsirkin wrote:
> On Tue, Apr 02, 2019 at 08:21:30PM +0200, David Hildenbrand wrote:
>> The other extreme is a system that barely frees (MAX_ORDER - X) pages,
>> however your thread will waste cycles scanning for such.
> I don't think we need to scan as such. An arch hook
> that queues a job to a wq only when there's work to
> do will fix the issue, right?

Well, even a system that is basically idle can theoretically free a
handful of pages every now and then you would like to report. There
would have to be a mechanism to detect if pages worth hinting have been
freed and need processing, IOW something like a callback after buddy
merging we are already dealing with.

That can then be a simple flag which the hinting thread considers (e.g.
wake up every X seconds to check if there is work) or kicking the
hinting thread like you suggest.



David / dhildenb