Re: [RFC] Add swappiness argument to memory.reclaim

[Roman Gushchin <roman.gushchin-fxUVXftIFDnyG1zEObXtfA@public.gmane.org>]

On Mon, May 16, 2022 at 03:29:42PM -0700, Yosry Ahmed wrote:
> The discussions on the patch series [1] to add memory.reclaim has
> shown that it is desirable to add an argument to control the type of
> memory being reclaimed by invoked proactive reclaim using
> memory.reclaim.
> 
> I am proposing adding a swappiness optional argument to the interface.
> If set, it overwrites vm.swappiness and per-memcg swappiness. This
> provides a way to enforce user policy on a stateless per-reclaim
> basis. We can make policy decisions to perform reclaim differently for
> tasks of different app classes based on their individual QoS needs. It
> also helps for use cases when particularly page cache is high and we
> want to mainly hit that without swapping out.
> 
> The interface would be something like this (utilizing the nested-keyed
> interface we documented earlier):
> 
> $ echo "200M swappiness=30" > memory.reclaim

What are the anticipated use cases except swappiness == 0 and
swappiness == system_default?

IMO it's better to allow specifying the type of memory to reclaim,
e.g. type="file"/"anon"/"slab", it's a way more clear what to expect.

E.g. what
$ echo "200M swappiness=1" > memory.reclaim
means if there is only 10M of pagecache? How much of anon memory will
be reclaimed?

Thanks!