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Thu, 30 Jan 2025 08:43:36 -0800 (PST) MIME-Version: 1.0 References: <20250129180633.3501650-1-yosry.ahmed@linux.dev> <20250129180633.3501650-3-yosry.ahmed@linux.dev> In-Reply-To: <20250129180633.3501650-3-yosry.ahmed@linux.dev> From: Nhat Pham Date: Thu, 30 Jan 2025 08:43:26 -0800 X-Gm-Features: AWEUYZm4BFGxHAow5GcdNZEfMlp7AvFEDULDBjH8He2bC6lpApDMAOQZJlKfIPQ Message-ID: Subject: Re: [PATCH v2 2/2] mm: zbud: remove zbud To: Yosry Ahmed Cc: Andrew Morton , Vitaly Wool , Seth Jennings , Dan Streetman , Miaohe Lin , Johannes Weiner , Chengming Zhou , Huacai Chen , WANG Xuerui , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Shakeel Butt , Vlastimil Babka , linux-mm@kvack.org, linux-kernel@vger.kernel.org, loongarch@lists.linux.dev, linux-s390@vger.kernel.org, linux-doc@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: C4CA64000D X-Stat-Signature: sr41sbxdqqeythk8katt57xknfa7o4zq X-Rspamd-Server: rspam08 X-Rspam-User: X-HE-Tag: 1738255417-417426 X-HE-Meta: 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 h/hs5OuS 5vb+cBOtQX5nZjOZB1oNGbvZBB/6+HV7TteI/MaRUNcZ/4jcQDINfYeBBd/s299hwSrHdVmmOAAzMIVu9J91BrV5/FkiuCRDqIZjR5JTLWU0BEG+8Wekfr6r6AlzLixeW1xYx7VXQCa2+MUmVoZTlv6fmBLIsA1/Rvvs6T8gp/JC4ZAVg2MvyiVcEugIVhlhkcY9Bg2MPQp5r4WyDVKeIKeHgt3XPQhQB+/w0ZYaWTYu77WTYTNxXeM8wWutckOACynIzzMfgOs4OoUFQ1KDyQ/qA5OEAOgOG1aRzH3mK/Ng2oRGbkVGruW69a3LOsbKp1Q+fzFmMQ9wZS6E5Ogs19ylm6QmBQI84vc8BkXIg+2SYxVw= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000816, 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 Wed, Jan 29, 2025 at 10:06=E2=80=AFAM 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. > > Remove zbud after z3fold's removal, leaving zsmalloc as the one and only > zpool allocator. Leave the removal of the zpool API (and its associated > config options) to a followup cleanup after no more allocators show up. > > Deprecating zbud for a few cycles before removing it was initially > proposed [2], like z3fold was marked as deprecated for 2 cycles [3]. > However, Johannes rightfully pointed out that the 2 cycles is too short > for most downstream consumers, and z3fold was deprecated first only as a > courtesy anyway. > > [1]https://lore.kernel.org/lkml/CAJD7tkbRF6od-2x_L8-A1QL3=3D2Ww13sCj4S3i4= bNndqF+3+_Vg@mail.gmail.com/ > [2]https://lore.kernel.org/lkml/Z5gdnSX5Lv-nfjQL@google.com/ > [3]https://lore.kernel.org/lkml/20240904233343.933462-1-yosryahmed@google= .com/ > > Signed-off-by: Yosry Ahmed Acked-by: Nhat Pham