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Tue, 30 May 2023 16:37:33 -0700 (PDT) MIME-Version: 1.0 References: <20230530222440.2777700-1-nphamcs@gmail.com> <20230530153006.8b73c276b1aaf5c3275f0b3f@linux-foundation.org> In-Reply-To: <20230530153006.8b73c276b1aaf5c3275f0b3f@linux-foundation.org> From: Nhat Pham Date: Tue, 30 May 2023 16:37:23 -0700 Message-ID: Subject: Re: [PATCH] zswap: do not shrink if cgroup may not zswap To: Andrew Morton 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: DF6901A0010 X-Stat-Signature: qyc16nmbjoyo9xsf5c7959e6mzjmk1ws X-HE-Tag: 1685489854-268739 X-HE-Meta: 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 PbqEFtbl fTz5UvfeEycQ3I1aQq1PJc8dSQ0mTOPrZZ2fCtIvBIKsC7c8FBP03EMKLSAmkpEkaV592ClGehBltupZJynJMmwO3Az+4wIYVlOMnGwBuJggjrOlS6ktJIs/MxidSlkrw+Rwyid6r5gNHSz3z9ZbWpn6gq1Fr/YzqbD3Z+KfXkX7H63bRDFWy+lPwffkOC4gorAq7sRMdrcXWznnAv6gbAch1OJIulF0HrKw5sOkrChRTp47NUV6Lc2lAXt0vIsdqZzIB7iGChMD27BoYq/EcAl6Y3QUVzTOQE2gQk/ZueD/ccvJQGmefeD9mbVSDXFaMhRwgz5odXK0cxJZC6wZvwLCOKLQoVipuHpIXPWKFoRDi1xSQnc13Afd1jyiPod0KWpWp/Kmj4acLQLRz0xAoBBGNIw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.019174, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, May 30, 2023 at 3:30=E2=80=AFPM Andrew Morton wrote: > > On Tue, 30 May 2023 15:24:40 -0700 Nhat Pham 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 i= s > > 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. >