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

[Minchan Kim]

On Tue, Nov 28, 2023 at 11:16:04AM +0100, Michal Hocko wrote:
> On Tue 28-11-23 09:31:06, Huang, Ying wrote:
> > Michal Hocko <mhocko@xxxxxxxx> writes:
> [...]
> > > 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?
> > 
> > If there are plenty free space in swap device, why not take advantage of
> > it?
> 
> Maybe a stupid question but what is the advantage of keeping around in
> the swap cache?

If the page is shared, we avoids addtional IO to bring them back so
swap cache.

If the page is still clean on reclaim moment since swap-in, VM doesn't
need to write them out to the swap disk since original data is already
there.