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Tue, 28 Jan 2025 08:04:39 -0800 (PST) X-Google-Smtp-Source: AGHT+IGqpPnsJFhxc42G1oeTcfqfAOFZmnXdusw+cHU7YmKoq+g3Kpg3lgQxvv7/0FFeXlJcUOiULKp35Dm+RVVOMDY= X-Received: by 2002:a05:6902:1206:b0:e58:11f6:db7b with SMTP id 3f1490d57ef6-e5811f6ec07mr20583386276.30.1738080278672; Tue, 28 Jan 2025 08:04:38 -0800 (PST) MIME-Version: 1.0 References: <42b24914-719a-4ff1-9d77-f6517717344f@suse.cz> In-Reply-To: From: Seth Jennings Date: Tue, 28 Jan 2025 10:04:27 -0600 X-Gm-Features: AWEUYZnK3ZHmW0BZFQQNIfrlt1GZ0ue7jpu1rb49U_i_mAa2mPxwtfiWv2J99-g Message-ID: Subject: Re: [PATCH 1/2] mm: zbud: deprecate CONFIG_ZBUD To: Yosry Ahmed Cc: Vlastimil Babka , Andrew Morton , Vitaly Wool , Miaohe Lin , Johannes Weiner , Nhat Pham , Chengming Zhou , Huacai Chen , Dan Streetman , WANG Xuerui , linux-mm@kvack.org, linux-kernel@vger.kernel.org, loongarch@lists.linux.dev X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: dv3YPmUr5CmVmG_h1lwUEkdM0puHeW74RzRE235SUP0_1738080279 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 7BD0F100020 X-Stat-Signature: 5hrgj3bnx96pm848a5tqwamjd83oiz5t X-Rspamd-Server: rspam08 X-Rspam-User: X-HE-Tag: 1738080281-696146 X-HE-Meta: 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 Z+zXpi4g l6sq9mF8LGPGGPJMQiJ84mJgBROnFWCMxTIw82EbKnQOrS/M6md9w1omhECy1+7tyek7hMXh0yvD5Rrdne79uxUqYtHJN+ToAvhB/y8mG4OTvL1RBOp+L2eYgCdOToTg2P6vwFpEXx9Zi/dXLGnsx7M71EY1edSnH6KPFtUXLm2VfOZts2ZM1brO8zT1mBsibMBTyaY/6PU+94fi3zsZrbAo8QYegnqWjN0krYJ1nGEUOABR6HDhYfCiUQugunEm7Vd/1C4g1kEheWde881uUNsK75JyQPXdHD7onw3d7NlFZlmEDEPbzni+Hfu6Y9C4ilXRZITY92d2ZlsMviUp76NeYuhFdj/kivBYjKe2DzL1X7AKEGPTkR+o7AQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Jan 28, 2025 at 9:37=E2=80=AFAM Yosry Ahmed = wrote: > > On Tue, Jan 28, 2025 at 11:21:10AM +0100, Vlastimil Babka wrote: > > On 1/28/25 00:58, Yosry Ahmed wrote: > > > The zbud compressed pages allocator is rarely used, most users use > > > zsmalloc. zbud consumes much more memory (only stores 1 or 2 compress= ed > > > pages per physical page). The only advantage of zbud is a marginal > > > performance improvement that by no means justify the memory overhead. > > > > > > Historically, zsmalloc had significantly worse latency than zbud and > > > z3fold but offered better memory savings. This is no longer the case= as > > > shown by a simple recent analysis [1]. In a kernel build test on tmp= fs > > > in a limited cgroup, zbud 2-3% less time than zsmalloc, but at the co= st > > > of using ~32% more memory (1.5G vs 1.13G). The tradeoff does not make > > > sense for zbud in any practical scenario. > > > > > > The only alleged advantage of zbud is not having the dependency on > > > CONFIG_MMU, but CONFIG_SWAP already depends on CONFIG_MMU anyway, and > > > zbud is only used by zswap. > > > > > > Following in the footsteps of [2], which deprecated z3fold, deprecate= d > > > zbud as planned and remove it in a few cycles if no objections are > > > raised from active users. > > > > > > Rename the user-visible config options so that users with CONFIG_ZBUD= =3Dy > > > get a new prompt with explanation during make oldconfig. Also, remove > > > CONFIG_ZBUD from defconfig. > > > > > > [1]https://lore.kernel.org/lkml/CAJD7tkbRF6od-2x_L8-A1QL3=3D2Ww13sCj4= S3i4bNndqF+3+_Vg@mail.gmail.com/ > > > [2]https://lore.kernel.org/lkml/20240904233343.933462-1-yosryahmed@go= ogle.com/ > > > > > > Signed-off-by: Yosry Ahmed > > > > Seems weird not to Cc the folks listed in MAINTAINERS for ZBUD? Unless = their > > addresses are known to bounce? > > Ugh I had them in the CC list, but I played around with it and probably > lost them :/ > > Seth, Dan, apologies. I haven't contributed in this space for quite some time so I defer to more active contributors on this. If it is true that zsmalloc has no/negligible deficiencies compared to zbud, it seems reasonable. > but at the cost of using ~32% more memory I do push back here as this % could be highly variable depending on the compressibility of the data. If the average compressibility is ~50%, zbud should be very memory efficien= t. If the average compressibility is very high or very low, it is less memory efficient. > > > And ZRAM maintainers should also be Ccd? > > ZRAM does not use zbud, I can definitely CC them but I don't want to be > a source of noise :) >