linux-kernel - Re: [External] Re: [PATCH] mm:zswap: fix zswap entry reclamation failure in two scenarios

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Message-ID: <CACSyD1Pn1HrJgG4XhSmrq7ROpHU5bO4SS6Szn+L5Nz1EjVxGZQ@mail.gmail.com>
Date:   Mon, 20 Nov 2023 10:42:15 +0800
From:   Zhongkun He <hezhongkun.hzk@...edance.com>
To:     Nhat Pham <nphamcs@...il.com>
Cc:     Chris Li <chrisl@...nel.org>, Yosry Ahmed <yosryahmed@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Seth Jennings <sjenning@...hat.com>,
        Dan Streetman <ddstreet@...e.org>,
        Vitaly Wool <vitaly.wool@...sulko.com>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>, Ying <ying.huang@...el.com>
Subject: Re: [External] Re: [PATCH] mm:zswap: fix zswap entry reclamation
 failure in two scenarios

>
> Shameless plug: zswap will much less likely hit the limit (global or
> cgroup) with the shrinker enabled ;) It will proactively reclaim the
> objects way ahead of the limit.

Hi  Nhat，glad to hear from you.
Back to the beginning, the original intention of this patch is to solve
the problem that shrink_work() fails to reclaim memory in two situations.
The zswap_writeback_entry() will failed for !page_was_allocated
because zswap_load will have two copies of the same page in memory
  (compressed and uncompressed) after faulting in a page from zswap when
zswap_exclusive_loads disabled.

A simple test:
1): Turn off  zswap_exclusive_loads_enabled.
2): Run a read-only program and allocate more memory than the limit,
so the limit will be reached and shrinker will fail.

>
> It comes with its own can of worms, of course - it's unlikely to work
> for all workloads in its current form, but perhaps worth experimenting
> with/improved upon?
>