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bh=L4WaZnpCGMusMfNexWgFq61vWT+q2ikrfQ3r1nuz2S0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=IwKTc81HJpslhXJQN5IEtsr3d+TJO57tr578zquodCfzAMkk/I/MoBv3tKbfaP/Gy RyO20aVk5oH3P80fJUR9n7XZrnv8lhbsPMnhn4DiffPpoghMmu654t22hbH7BnSSKj 3q74qIvseKB9kf0ndga4hv//j0yIQBcO0VlEdmJA= Date: Tue, 30 May 2023 15:30:06 -0700 From: Andrew Morton To: Nhat Pham 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 Message-Id: <20230530153006.8b73c276b1aaf5c3275f0b3f@linux-foundation.org> In-Reply-To: <20230530222440.2777700-1-nphamcs@gmail.com> References: <20230530222440.2777700-1-nphamcs@gmail.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 4BEF540012 X-Rspam-User: X-Stat-Signature: iuuqmw4ycxpnju8yox5x8fbeo1g8ke34 X-Rspamd-Server: rspam01 X-HE-Tag: 1685485809-301131 X-HE-Meta: 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 38pGto6I wAmEyli5kG6EaGayO/Tk/okE/5CiOJYU8PQJJ7t2dhBo38gYL6LZxDbm8lQpljqz15auppItsy5iW6fdPnqE8shCNoKHFy1JYEsKSl1xR3KyGdeDCzDyWaoi8ixfUwgr+lFmnztl14IaqSV0orwShgwReulqKYD3AR4WAxJspv9zduxAmsPF5SAMukSAV0/+5X9Xdu+FWoWyyk//SZ/BKtDIzka6X8ZwxEVmPzAoGL+JwhHSQIGpCjuvFghbHsQJ4HyyKiGV5kx17/8b/9dfHqCX3L2GYqFWFeuzWfuY3ZRrqBKI8CKAgvKSj53rMGwlwQuovzJvcl0tasRxu5Cj8/IvZoLCQvKtD1YrI X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 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? > This patch fixes the issue by rejecting zswap store attempt without > shrinking the pool when obj_cgroup_may_zswap() returns false.