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From: Shakeel Butt To: Yosry Ahmed Cc: Andrew Morton , 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 Subject: Re: [PATCH 1/2] mm: zbud: deprecate CONFIG_ZBUD Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 837FE120002 X-Stat-Signature: hp7j8z8a7t84s7778uzjxfdgbkd71ba5 X-Rspam-User: X-HE-Tag: 1738083470-260022 X-HE-Meta: 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 HO9PeWku scSXF8bbm8cSFCBRBiRgzOBvLw+kq157X6bOGnFsEOfetjNNiM1u6mbHexDQtzc+0ssXWbTRCedKoLb5Bd/Ji/8OfW+qTVCC3wowovb5SFhwggMj0yw27iwIUPPa6pGwKRchaF7esO9u5Njc3LwvVL33LbYkzlSGyOqyj0sRt95Xrokyf2hQlFzStD+MQr1pG4J1fnIVGDeDGC91XK9PqAOqlz7hN4tty3GKgY2kYi3bRiC+fFHL3zKAPQzCHbC66FrXXX/3TwD6QnQ9VSP+EQwCuq5cHUSdWgOtmxmXDjImCYlL4pg+GwfyqM9Rhoe9D1I/I8Mqj1Ia9VvRsyZeXRi9fxA== 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 Mon, Jan 27, 2025 at 11:58:21PM +0000, 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 Reviewed-by: Shakeel Butt