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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4E4E4C7619A for ; Wed, 12 Apr 2023 12:24:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229615AbjDLMYW (ORCPT ); Wed, 12 Apr 2023 08:24:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34206 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229769AbjDLMYU (ORCPT ); Wed, 12 Apr 2023 08:24:20 -0400 Received: from out30-133.freemail.mail.aliyun.com (out30-133.freemail.mail.aliyun.com [115.124.30.133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6593B76B4 for ; Wed, 12 Apr 2023 05:24:07 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R261e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046056;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0VfwS.8H_1681302242; Received: from 30.97.48.75(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0VfwS.8H_1681302242) by smtp.aliyun-inc.com; Wed, 12 Apr 2023 20:24:04 +0800 Message-ID: Date: Wed, 12 Apr 2023 20:24:07 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.9.1 Subject: Re: [PATCH] mm/page_alloc: consider pfn holes after pfn_valid() in __pageblock_pfn_to_page() To: Michal Hocko Cc: akpm@linux-foundation.org, mgorman@techsingularity.net, vbabka@suse.cz, david@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <62e231a8f2e50c04dcadc7a0cfaa6dea5ce1ec05.1681296022.git.baolin.wang@linux.alibaba.com> From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/12/2023 7:15 PM, Michal Hocko wrote: > On Wed 12-04-23 18:45:31, Baolin Wang wrote: >> Now the __pageblock_pfn_to_page() is used by set_zone_contiguous(), >> which checks whether the given zone contains holes, and uses pfn_valid() >> to check if the end pfn is valid. However pfn_valid() can not make sure >> the end pfn is not a hole if the size of a pageblock is larger than the >> size of a sub-mem_section, since the struct page getting by pfn_to_page() >> may represent a hole or an unusable page frame, which may cause incorrect >> zone contiguous is set. >> >> Though another user of pageblock_pfn_to_page() in compaction seems work >> well now, it is better to avoid scanning or touching these offline pfns. >> So like commit 2d070eab2e82 ("mm: consider zone which is not fully >> populated to have holes"), we should also use pfn_to_online_page() for >> the end pfn to make sure it is a valid pfn with usable page frame. >> Meanwhile the pfn_valid() for end pfn can be dropped now. >> >> Moreover we've already used pfn_to_online_page() for start pfn to make >> sure it is online and valid, so the pfn_valid() for the start pfn is >> unnecessary, drop it. > > Is this a theoretical problem or something you have encountered on a > real machine? Could you provide more details please? As I replied to David, this is just from code inspection when trying to remove the unnecessary pfn_valid() in __pageblock_pfn_to_page().