Received: by 2002:a05:6a10:6d10:0:0:0:0 with SMTP id gq16csp996899pxb; Wed, 13 Apr 2022 17:50:49 -0700 (PDT) X-Google-Smtp-Source: ABdhPJxGOszhmMjEVY2HJTTx/b/6NnywMrhj0XcVyuMVpEF2jebD9VmhOEN2CTxys99i8eUOMgcJ X-Received: by 2002:a05:6402:331c:b0:41d:9354:97c2 with SMTP id e28-20020a056402331c00b0041d935497c2mr279810eda.300.1649897449698; Wed, 13 Apr 2022 17:50:49 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1649897449; cv=none; d=google.com; s=arc-20160816; b=rLe1K/gqNoTgN1uK9+jeL7S1JMhYlSgA+yM0AinOF9U7MzMdxiNLGvI9oRdEoUNJ0N AwKNfP/75NkxUycUOeFtHCZrTPCMwHfPwBFExnEAV5M7sWku9deiumVQciaWbEJWM2dL jNo5q6sTolsZvM/+upum+Qfi10pAk/clA82LlZujPFb3XWC0TccbvXUJeF43abIIAaOp mMCG7Q0QXRioAnfsTOBAa1ZriO5g82rmtos5H9+F3tL79HZrizo1BRK49RwVHHW3GwWv jiBkBhRx6ZDmyuUAZTZMsMth9rFF6rG6ThrinKMPYlPX97tdntiDLIBKmfSF5go2eSlh SDdg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:content-transfer-encoding:mime-version :references:in-reply-to:message-id:subject:cc:to:from:date :dkim-signature; bh=1HPwJP8kwBS/940AJab0LxF+WoGUv5nzjcjGdLq7Czs=; b=rfxwfShGgb1BgMVrCdOx9/u2r48Nsy1ups0mrQ2GPkS0jH6JrCVKacWCO3biHSr9UO VzjD6uIolmuJoZfpSktCdW4oB5k51QPUJOrBzPxIicPDRVcdCrbM3wHv5qOvdN9r+eT+ 6bKZGNq3V2e7e7MUz8FtN9bjzUTyfmXws71+TsvE/6gD4TqNQYf72RzFPtZeIC6KKfHz nt/5QHdX9LgcBh4dxCxJJwX8hK/7q/QOMli+Xir/0E02VSbFru5aZnuO9Ax1AWImfyca gdXQTPj5YYK/axIjoCDOP/JjGsu5PQtN/0D1YkaxZPiQShnUZniweHkDsvaJppR4DuSZ nmaw== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@linux-foundation.org header.s=korg header.b="SqqwH/IL"; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Return-Path: Received: from out1.vger.email (out1.vger.email. [2620:137:e000::1:20]) by mx.google.com with ESMTP id t4-20020a056402524400b0041d793e0d4asi2883425edd.318.2022.04.13.17.50.24; Wed, 13 Apr 2022 17:50:49 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@linux-foundation.org header.s=korg header.b="SqqwH/IL"; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238199AbiDMTPu (ORCPT + 99 others); Wed, 13 Apr 2022 15:15:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48010 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239135AbiDMTOF (ORCPT ); Wed, 13 Apr 2022 15:14:05 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 76BAA48E5B; Wed, 13 Apr 2022 12:10:55 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 3026AB82761; Wed, 13 Apr 2022 19:10:54 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 59C03C385A3; Wed, 13 Apr 2022 19:10:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1649877053; bh=7zffni3b6WrTkbJ/vkGXvRk4tdERsTcUIscgc872JCQ=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=SqqwH/ILeJhcYHRxq2AClOf8Giw69xPlpG9aNeHURMMSzmwK4WpuapedIeUPEC9+1 8PiG87qt/kuClb3p6ErUbd2GuAIWw7YlDCQF4u2BiMVfsaHuYzCZUwJGEr1b8uXtqi NLCeoVYVhofr6h4dBfWKxp5jWITD4C0bA8pfpC+A= Date: Wed, 13 Apr 2022 12:10:51 -0700 From: Andrew Morton To: Muchun Song Cc: corbet@lwn.net, mike.kravetz@oracle.com, mcgrof@kernel.org, keescook@chromium.org, yzaikin@google.com, osalvador@suse.de, david@redhat.com, masahiroy@kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, duanxiongchun@bytedance.com, smuchun@gmail.com Subject: Re: [PATCH v8 4/4] mm: hugetlb_vmemmap: add hugetlb_optimize_vmemmap sysctl Message-Id: <20220413121051.a363193c726451115c634a69@linux-foundation.org> In-Reply-To: <20220413144748.84106-5-songmuchun@bytedance.com> References: <20220413144748.84106-1-songmuchun@bytedance.com> <20220413144748.84106-5-songmuchun@bytedance.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-8.4 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,NICE_REPLY_A,RCVD_IN_DNSWL_HI, SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 13 Apr 2022 22:47:48 +0800 Muchun Song wrote: > We must add hugetlb_free_vmemmap=on (or "off") to the boot cmdline and > reboot the server to enable or disable the feature of optimizing vmemmap > pages associated with HugeTLB pages. However, rebooting usually takes a > long time. So add a sysctl to enable or disable the feature at runtime > without rebooting. Do we really need this feature? Really? What's the use case and what is the end-user value? Presumably CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP worsens things for some setups/workloads? Please tell us much more about that. What is the magnitude of the deoptimization?