From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4474EC433F5 for ; Wed, 13 Apr 2022 19:10:57 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id B28F36B0072; Wed, 13 Apr 2022 15:10:56 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id AD7346B0073; Wed, 13 Apr 2022 15:10:56 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 99E416B0074; Wed, 13 Apr 2022 15:10:56 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0224.hostedemail.com [216.40.44.224]) by kanga.kvack.org (Postfix) with ESMTP id 8BDB46B0072 for ; Wed, 13 Apr 2022 15:10:56 -0400 (EDT) Received: from smtpin23.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 423B9AA492 for ; Wed, 13 Apr 2022 19:10:56 +0000 (UTC) X-FDA: 79352798112.23.D44D1F9 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by imf04.hostedemail.com (Postfix) with ESMTP id 951FA40008 for ; Wed, 13 Apr 2022 19:10:55 +0000 (UTC) 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 43F6FB82763; 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-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: gygaugithe1kugen658pb3o3brwbabrn Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b="SqqwH/IL"; dmarc=none; spf=pass (imf04.hostedemail.com: domain of akpm@linux-foundation.org designates 145.40.68.75 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org X-Rspamd-Queue-Id: 951FA40008 X-HE-Tag: 1649877055-833992 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: 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?