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From: Nhat Pham <nphamcs@gmail.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: hannes@cmpxchg.org, cerasuolodomenico@gmail.com,
	linux-mm@kvack.org,  linux-kernel@vger.kernel.org,
	sjenning@redhat.com, ddstreet@ieee.org,
	 vitaly.wool@konsulko.com, yosryahmed@google.com,
	kernel-team@meta.com
Subject: Re: [PATCH] zswap: do not shrink if cgroup may not zswap
Date: Tue, 30 May 2023 16:37:23 -0700	[thread overview]
Message-ID: <CAKEwX=OBtWfcYJkCTM0QE-P+u-AvzkSe+C9QqmLxdDMxSS_45Q@mail.gmail.com> (raw)
In-Reply-To: <20230530153006.8b73c276b1aaf5c3275f0b3f@linux-foundation.org>

On Tue, May 30, 2023 at 3:30 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Tue, 30 May 2023 15:24:40 -0700 Nhat Pham <nphamcs@gmail.com> wrote:
>
> > Before storing a page, zswap first checks if the number of stored pages
> > exceeds the limit specified by memory.zswap.max, for each cgroup in the
> > hierarchy. If this limit is reached or exceeded, then zswap shrinking is
> > triggered and short-circuits the store attempt.
> >
> > However, since the zswap's LRU is not memcg-aware, this can create the
> > following pathological behavior: the cgroup whose zswap limit is
> > reached will evict pages from other cgroups continually, without
> > lowering its own zswap usage. This means the shrinking will continue
> > until the need for swap ceases or the pool becomes empty.
> >
> > As a result of this, we observe a disproportionate amount of zswap
> > writeback and a perpetually small zswap pool in our experiments, even
> > though the pool limit is never hit.
>
> That sounds unpleasant.  Do you think the patch should be backported
> into earlier (-stable) kernels?

I think it should be, for any kernel version after f4840ccfca25.



>
> > This patch fixes the issue by rejecting zswap store attempt without
> > shrinking the pool when obj_cgroup_may_zswap() returns false.
>


  reply	other threads:[~2023-05-30 23:37 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-05-30 16:21 [PATCH] zswap: do not shrink when memory.zswap.max is 0 Nhat Pham
2023-05-30 16:52 ` Yosry Ahmed
2023-05-30 18:00   ` Johannes Weiner
2023-05-30 18:41     ` Yosry Ahmed
2023-05-30 19:13       ` Johannes Weiner
2023-05-30 20:19         ` Yosry Ahmed
2023-05-30 20:59           ` Johannes Weiner
2023-05-30 21:04             ` Yosry Ahmed
2023-05-30 21:46               ` Nhat Pham
2023-05-30 22:24                 ` [PATCH] zswap: do not shrink if cgroup may not zswap Nhat Pham
2023-05-30 22:30                   ` Andrew Morton
2023-05-30 23:37                     ` Nhat Pham [this message]
2023-05-30 22:36                   ` Yosry Ahmed
2023-05-30 23:24                     ` [PATCH v3] " Nhat Pham
2023-05-30 18:27   ` [PATCH] zswap: do not shrink when memory.zswap.max is 0 Nhat Pham
2023-05-30 18:42     ` Yosry Ahmed
2023-06-07 19:09       ` Andrew Morton
2023-06-07 19:17         ` Yosry Ahmed
2023-06-07 19:31         ` Nhat Pham
2023-06-07 20:42         ` Johannes Weiner

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