Re: [RFC 0/4] Introduce unbalance proactive reclaim

[Michal Hocko]

On Wed 08-11-23 14:58:11, Huan Yang wrote:
> In some cases, we need to selectively reclaim file pages or anonymous
> pages in an unbalanced manner.
> 
> For example, when an application is pushed to the background and frozen,
> it may not be opened for a long time, and we can safely reclaim the
> application's anonymous pages, but we do not want to touch the file pages.

Could you explain why? And also why do you need to swap out in that
case?
 
> This patchset extends the proactive reclaim interface to achieve
> unbalanced reclamation. Users can control the reclamation tendency by
> inputting swappiness under the original interface. Specifically, users
> can input special values to extremely reclaim specific pages.

Other have already touched on this in other replies but v2 doesn't have
a per-memcg swappiness

> Example:
>   	echo "1G" 200 > memory.reclaim (only reclaim anon)
> 	  echo "1G" 0  > memory.reclaim (only reclaim file)
> 	  echo "1G" 1  > memory.reclaim (only reclaim file)
> 
> Note that when performing unbalanced reclamation, the cgroup swappiness
> will be temporarily adjusted dynamically to the input value. Therefore,
> if the cgroup swappiness is further modified during runtime, there may
> be some errors.

In general this is a bad semantic. The operation shouldn't have side
effect that are potentially visible for another operation.
-- 
Michal Hocko
SUSE Labs