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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 05A5AC433B4 for ; Wed, 21 Apr 2021 07:34:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B6E8C600CD for ; Wed, 21 Apr 2021 07:33:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235604AbhDUHeb (ORCPT ); Wed, 21 Apr 2021 03:34:31 -0400 Received: from mx2.suse.de ([195.135.220.15]:54590 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234038AbhDUHea (ORCPT ); Wed, 21 Apr 2021 03:34:30 -0400 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 D932AAFE6; Wed, 21 Apr 2021 07:33:56 +0000 (UTC) Date: Wed, 21 Apr 2021 09:33:52 +0200 From: Oscar Salvador To: Muchun Song Cc: Jonathan Corbet , Mike Kravetz , Thomas Gleixner , Ingo Molnar , bp@alien8.de, X86 ML , hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, Peter Zijlstra , Alexander Viro , Andrew Morton , paulmck@kernel.org, pawan.kumar.gupta@linux.intel.com, Randy Dunlap , oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de, Mina Almasry , David Rientjes , Matthew Wilcox , Michal Hocko , "Song Bao Hua (Barry Song)" , David Hildenbrand , HORIGUCHI =?utf-8?B?TkFPWUEo5aCA5Y+jIOebtOS5nyk=?= , Joao Martins , Xiongchun duan , fam.zheng@bytedance.com, linux-doc@vger.kernel.org, LKML , Linux Memory Management List , linux-fsdevel Subject: Re: [External] Re: [PATCH v20 8/9] mm: memory_hotplug: disable memmap_on_memory when hugetlb_free_vmemmap enabled Message-ID: <20210421073346.GA22456@linux> References: <20210415084005.25049-1-songmuchun@bytedance.com> <20210415084005.25049-9-songmuchun@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Wed, Apr 21, 2021 at 11:41:24AM +0800, Muchun Song wrote: > > Documentation/admin-guide/kernel-parameters.txt already provides an > > explanation on memory_hotplug.memmap_on_memory parameter that states > > that the feature cannot be enabled when using hugetlb-vmemmap > > optimization. > > > > Users can always check whether the feature is enabled via > > /sys/modules/memory_hotplug/parameters/memmap_on_memory. Heh, I realized this is not completely true. Users can check whether the feature is __enabled__ by checking the sys fs, but although it is enabled, it might not be effective. This might be due to a different number of reasons, vmemmap does not fully span a PMD, the size we want to add spans more than a single memory block, etc. That is what "Note that even when enabled, there are a few cases where the feature is not effective." is supposed to mean. Anyway, I did not change my opionion on this. Thanks -- Oscar Salvador SUSE L3