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 2B3B6C433EF for ; Mon, 4 Apr 2022 09:26:20 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 95FC36B0072; Mon, 4 Apr 2022 05:26:09 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 90EFE6B0073; Mon, 4 Apr 2022 05:26:09 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8250E6B0074; Mon, 4 Apr 2022 05:26:09 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.hostedemail.com [64.99.140.28]) by kanga.kvack.org (Postfix) with ESMTP id 7358C6B0072 for ; Mon, 4 Apr 2022 05:26:09 -0400 (EDT) Received: from smtpin03.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id BD00C21A2B for ; Mon, 4 Apr 2022 09:25:58 +0000 (UTC) X-FDA: 79318664796.03.B95E5B4 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf04.hostedemail.com (Postfix) with ESMTP id 2C9BA40043 for ; Mon, 4 Apr 2022 09:25:58 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6636A1FB; Mon, 4 Apr 2022 02:25:57 -0700 (PDT) Received: from [10.163.37.159] (unknown [10.163.37.159]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C533F3F718; Mon, 4 Apr 2022 02:25:51 -0700 (PDT) Message-ID: Date: Mon, 4 Apr 2022 14:56:17 +0530 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Subject: Re: [PATCH v4 2/2] arm64: mm: hugetlb: Enable HUGETLB_PAGE_FREE_VMEMMAP for arm64 Content-Language: en-US To: Muchun Song , will@kernel.org, akpm@linux-foundation.org, david@redhat.com, bodeddub@amazon.com, osalvador@suse.de, mike.kravetz@oracle.com, rientjes@google.com, mark.rutland@arm.com, catalin.marinas@arm.com, james.morse@arm.com, 21cnbao@gmail.com Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, duanxiongchun@bytedance.com, fam.zheng@bytedance.com, smuchun@gmail.com References: <20220331065640.5777-1-songmuchun@bytedance.com> <20220331065640.5777-2-songmuchun@bytedance.com> From: Anshuman Khandual In-Reply-To: <20220331065640.5777-2-songmuchun@bytedance.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: 8i1zep1p1whzfcpdwhmdgbc1t5opnauy Authentication-Results: imf04.hostedemail.com; dkim=none; spf=pass (imf04.hostedemail.com: domain of anshuman.khandual@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=anshuman.khandual@arm.com; dmarc=pass (policy=none) header.from=arm.com X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 2C9BA40043 X-HE-Tag: 1649064358-738691 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000179, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Hello Muchun, On 3/31/22 12:26, Muchun Song wrote: > The feature of minimizing overhead of struct page associated with each > HugeTLB page aims to free its vmemmap pages (used as struct page) to > save memory, where is ~14GB/16GB per 1TB HugeTLB pages (2MB/1GB type). Enabling this feature saves us around 1.4/1.6 % memory but looking from other way around, unavailability of vmemmap backing pages (~1.4GB) when freeing up a corresponding HugeTLB page, could prevent ~1TB memory from being used as normal page form (requiring their own struct pages), thus forcing the HugeTLB page to remain as such ? Is not this problematic ? These additional 1TB memory in normal pages, from a HugeTLB dissolution could have eased the system's memory pressure without this feature being enabled. - Anshuman