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Sender: Minchan Kim <minchan.kim@gmail.com>
Date:   Tue, 28 Nov 2023 14:45:09 -0800
From:   Minchan Kim <minchan@kernel.org>
To:     Michal Hocko <mhocko@suse.com>
Cc:     "Huang, Ying" <ying.huang@intel.com>,
        Yosry Ahmed <yosryahmed@google.com>,
        Liu Shixin <liushixin2@huawei.com>,
        Yu Zhao <yuzhao@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Sachin Sant <sachinp@linux.ibm.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Kefeng Wang <wangkefeng.wang@huawei.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v10] mm: vmscan: try to reclaim swapcache pages if no
 swap space
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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@suse.com> 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.