Re: [PATCH v10] mm: vmscan: try to reclaim swapcache pages if no swap space

Michal Hocko
2023-11-27T09:10:57Z

On Mon 27-11-23 10:34:46, Huang, Ying wrote:
> Michal Hocko <mhocko@suse.com> writes:
>
> > On Thu 23-11-23 14:15:59, Huang, Ying wrote:
> >> Michal Hocko <mhocko@suse.com> writes:
> > [...]
> >> > Yes swapcache pages are indeed more complicated but most of the time
> >> > they just go away as well, no?
> >>
> >> When we swapin a page, we will put it in swapcache too. And the page
> >> can be in that state for long time if there is more than 50% free space
> >> in the swap device.
> >
> > True, but why is that a problem? If you encounter such a swapped in page
> > on the file LRU then the page should be referened and as such should be
> > activated, no?
>
> This just means that anonymous pages in file LRU aren't temporary or
> short-term. So we need to consider that.

Right. On the other hand we could be more aggressive when dropping the
swapcache. Is there any actual reason why we cannot try to folio_free_swap
even when mem_cgroup_swap_full == F?
--
Michal Hocko
SUSE Labs