Re: [PATCH RFC] fs: drop_caches: introduce per-node drop_caches interface

[Michal Hocko <mhocko@suse.com>]

On Thu 09-04-26 16:54:48, Kefeng Wang wrote:
> 
> 
> On 4/9/2026 4:22 PM, Michal Hocko wrote:
> > On Thu 09-04-26 16:08:37, Kefeng Wang wrote:
> > [...]
> > > To use the reclaim interface, there are two differences,
> > > 
> > > 1) we need to input the reclaim numbers and swappiness, this is not a big
> > > problem
> > > 2) for reclaim, it supports swappiness=max to only reclaim anonymous pages,
> > > but cannot only reclaim file pages,
> > 
> > Why is 2) a real constrain?
> 
> This should not be a restriction, but a strategy. Our product wants to
> migrate anonymous pages to the local instead of swapping them out. However,
> the current per-node-reclaim interface does not support reclaiming only file
> pages.

Yes, I do understand that you want to keep your hot anonymous pages
resident on some node. Those shouldn't be reclaimed by the user space
triggered reclaim anyway, right? Migration will then happen during the
memory offlining.

This will certainly require some fine tuning but I do not see any reason
this should be completely impossible. Certainly a more robust way (from
API POV) than the suggested drop_caches. I am also not convinced we need
page-cache-only reclaim for the existing reclaim interface. I believe it
makes more sense to look at the reclaim from hotness POV rather than
anon vs. file.
-- 
Michal Hocko
SUSE Labs