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

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Message-ID: <ZWRdG49vlGzSY_Uj@tiehlicka>
Date:   Mon, 27 Nov 2023 10:10:51 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     Yosry Ahmed <yosryahmed@...gle.com>,
        Liu Shixin <liushixin2@...wei.com>,
        Yu Zhao <yuzhao@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Sachin Sant <sachinp@...ux.ibm.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Kefeng Wang <wangkefeng.wang@...wei.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10] mm: vmscan: try to reclaim swapcache pages if no
 swap space

On Mon 27-11-23 10:34:46, Huang, Ying wrote:
> Michal Hocko <mhocko@...e.com> writes:
> 
> > On Thu 23-11-23 14:15:59, Huang, Ying wrote:
> >> Michal Hocko <mhocko@...e.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