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 X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4006EC64E69 for ; Tue, 17 Nov 2020 19:46:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 058A62222E for ; Tue, 17 Nov 2020 19:46:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731120AbgKQTpe (ORCPT ); Tue, 17 Nov 2020 14:45:34 -0500 Received: from mx2.suse.de ([195.135.220.15]:47558 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730564AbgKQTpY (ORCPT ); Tue, 17 Nov 2020 14:45:24 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 00F9FABDE; Tue, 17 Nov 2020 19:45:23 +0000 (UTC) MIME-Version: 1.0 Date: Tue, 17 Nov 2020 20:45:21 +0100 From: Oscar Salvador To: Muchun Song Cc: "Song Bao Hua (Barry Song)" , corbet@lwn.net, mike.kravetz@oracle.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, viro@zeniv.linux.org.uk, akpm@linux-foundation.org, paulmck@kernel.org, mchehab+huawei@kernel.org, pawan.kumar.gupta@linux.intel.com, rdunlap@infradead.org, oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de, almasrymina@google.com, rientjes@google.com, willy@infradead.org, mhocko@suse.com, duanxiongchun@bytedance.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: Re: [External] RE: [PATCH v4 00/21] Free some vmemmap pages of hugetlb page In-Reply-To: References: <20201113105952.11638-1-songmuchun@bytedance.com> <349168819c1249d4bceea26597760b0a@hisilicon.com> <714ae7d701d446259ab269f14a030fe9@hisilicon.com> User-Agent: Roundcube Webmail Message-ID: X-Sender: osalvador@suse.de Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-11-17 17:29, Muchun Song wrote: > Now for the 2MB HugrTLB page, we only free 6 vmemmap pages. > But your words woke me up. Maybe we really can free 7 vmemmap > pages. In this case, we can see 8 of the 512 struct page structures > has beed set PG_head flag. If we can adjust compound_head() > slightly and make compound_head() return the real head struct > page when the parameter is the tail struct page but with PG_head > flag set. I will start an investigation and a test. I would not overcomplicate things at this stage, but rather keep it simple as the code is already tricky enough(without counting the LOC thatvit adds). We can always build on top later on in order to improve things. -- Oscar Salvador SUSE L3