Re: [PATCH v16.1 0/9] mm / virtio: Provide support for free page reporting

[Dave Hansen]

On 1/23/20 8:26 AM, Alexander Duyck wrote:
>> The big piece I'm missing is the page cache. Linux will by default try 
>> to keep the free list as small as it can in favor of page cache, so most 
>> of the benefit of this patch set will be void in real world scenarios.
> Agreed. This is a the next piece of this I plan to work on once this is
> accepted. For now the quick and dirty approach is to essentially make use
> of the /proc/sys/vm/drop_caches interface in the guest by either putting
> it in a cronjob somewhere or to have it after memory intensive workloads.

There was an implementation in "Clear Linux" that used this sysctl:

> https://github.com/Conan-Kudo/omv-kernel-rc/blob/master/0154-sysctl-vm-Fine-grained-cache-shrinking.patch

(I can't find it in the Clear repos at the moment, must not be used
currently).  But the idea was to have a little daemon in the host that
periodically applied some artificial pressure with this sysctl.  This
sysctl is a smaller hammer than /proc/sys/vm/drop_caches and lets you
drop small amounts of cache.

The right way to do it is probably to do real, generic reclaim instead
of drop_caches.

This isn't conceptually *that* far away from the "proactive reclaim"
that other folks have proposed:

	https://lwn.net/Articles/787611/