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Tue, 28 Jan 2025 10:21:11 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id ybdDBJevmGfrbAAAD6G6ig (envelope-from ); Tue, 28 Jan 2025 10:21:11 +0000 Message-ID: <42b24914-719a-4ff1-9d77-f6517717344f@suse.cz> Date: Tue, 28 Jan 2025 11:21:10 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm: zbud: deprecate CONFIG_ZBUD Content-Language: en-US To: Yosry Ahmed , Andrew Morton Cc: Vitaly Wool , Miaohe Lin , Johannes Weiner , Nhat Pham , Chengming Zhou , Huacai Chen , WANG Xuerui , linux-mm@kvack.org, linux-kernel@vger.kernel.org, loongarch@lists.linux.dev References: From: Vlastimil Babka In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspamd-Queue-Id: 2A22918000E X-Stat-Signature: 4bpj5zrdgfx8p5gr9h4g5spgx33rqwx7 X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1738059673-639159 X-HE-Meta: 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 2YZdb/jC YYOobanupRRNt+CLFYK7QtRop6+Wc8r3azh279S5UtgnPGtM30B/SGYHd2dEQWTxyepKH8gGSDmZUEP3Eck5EnxqmCHpUoX4+iksCQWI+MdUcfraT4ii11PAgpCD3HjzHLnSGfqevXl40Y7HosRhQvoJKrrZIMCCRLi6kzNIPcxni4rEHutMk6AIX7jfgc5lafOxvET81kKxxb9vuQHeyCliUxa7qfCy+ZocBQD/nQ9RY3HaASCVk1dp/RSj+2PmvRNozAJ6wMoGS5fdFpTtlJIZBnRh6E2fRfPW7HsYpNMFB0U0bPDKqyk/jZKnJ884aQFLrl8tv4LG4NFPcNw6qsCpyfF1r4rio17yq+NToXVmh1Jb+9xW24c1gRbv68NGKYlFubgc/itKDp0pfelALZ/M5Qw== 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 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 compressed > 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 tmpfs > in a limited cgroup, zbud 2-3% less time than zsmalloc, but at the cost > 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, deprecated > 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=y > 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=2Ww13sCj4S3i4bNndqF+3+_Vg@mail.gmail.com/ > [2]https://lore.kernel.org/lkml/20240904233343.933462-1-yosryahmed@google.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? And ZRAM maintainers should also be Ccd?