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

[Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org>]

On Mon 16-05-22 15:29:42, 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.

Can you be more specific about the usecase please? Also how do you
define the semantic? Behavior like vm_swappiness is rather vague because
the kernel is free to ignore (and it does indeed) this knob in many
situations. What is the expected behavior when user explicitly requests
a certain swappiness?
-- 
Michal Hocko
SUSE Labs