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[2a03:2880:ff:14::face:b00c]) by smtp.gmail.com with ESMTPSA id j20-20020a056a00235400b006d6b6c0b569sm358349pfj.219.2023.12.20.16.57.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 20 Dec 2023 16:57:26 -0800 (PST) From: Nhat Pham To: akpm@linux-foundation.org Cc: tj@kernel.org, lizefan.x@bytedance.com, hannes@cmpxchg.org, cerasuolodomenico@gmail.com, yosryahmed@google.com, sjenning@redhat.com, ddstreet@ieee.org, vitaly.wool@konsulko.com, mhocko@kernel.org, roman.gushchin@linux.dev, shakeelb@google.com, muchun.song@linux.dev, hughd@google.com, corbet@lwn.net, konrad.wilk@oracle.com, senozhatsky@chromium.org, rppt@kernel.org, linux-mm@kvack.org, kernel-team@meta.com, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, david@ixit.cz Subject: [PATCH v6] zswap: memcontrol: implement zswap writeback disabling (fix) Date: Wed, 20 Dec 2023 16:57:25 -0800 Message-Id: <20231221005725.3446672-1-nphamcs@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20231207192406.3809579-1-nphamcs@gmail.com> References: <20231207192406.3809579-1-nphamcs@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Add a caveat about recurring zswap store failures leading to reclaim inefficiency. Suggested-by: Yosry Ahmed Signed-off-by: Nhat Pham Acked-by: Chris Li --- Documentation/admin-guide/cgroup-v2.rst | 5 ++++- Documentation/admin-guide/mm/zswap.rst | 4 ++++ 2 files changed, 8 insertions(+), 1 deletion(-) diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-= guide/cgroup-v2.rst index 2b4ac43efdc8..5ec7dd753cd1 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -1686,7 +1686,10 @@ PAGE_SIZE multiple when read back. =20 When this is set to 0, all swapping attempts to swapping devices are disabled. This included both zswap writebacks, and swapping due - to zswap store failure. + to zswap store failures. If the zswap store failures are recurring + (for e.g if the pages are incompressible), users can observe + reclaim inefficiency after disabling writeback (because the same + pages might be rejected again and again). =20 Note that this is subtly different from setting memory.swap.max to 0, as it still allows for pages to be written to the zswap pool. diff --git a/Documentation/admin-guide/mm/zswap.rst b/Documentation/admin-g= uide/mm/zswap.rst index cfa653130346..b42132969e31 100644 --- a/Documentation/admin-guide/mm/zswap.rst +++ b/Documentation/admin-guide/mm/zswap.rst @@ -159,6 +159,10 @@ zswap itself) on a cgroup-basis as follows: =20 echo 0 > /sys/fs/cgroup//memory.zswap.writeback =20 +Note that if the store failures are recurring (for e.g if the pages are +incompressible), users can observe reclaim inefficiency after disabling +writeback (because the same pages might be rejected again and again). + When there is a sizable amount of cold memory residing in the zswap pool, = it can be advantageous to proactively write these cold pages to swap and recl= aim the memory for other use cases. By default, the zswap shrinker is disabled. --=20 2.34.1