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=-7.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,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 E225FC433E0 for ; Wed, 6 Jan 2021 19:31:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B4B5B2311B for ; Wed, 6 Jan 2021 19:31:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727103AbhAFTbY (ORCPT ); Wed, 6 Jan 2021 14:31:24 -0500 Received: from aserp2130.oracle.com ([141.146.126.79]:52030 "EHLO aserp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726490AbhAFTbX (ORCPT ); Wed, 6 Jan 2021 14:31:23 -0500 Received: from pps.filterd (aserp2130.oracle.com [127.0.0.1]) by aserp2130.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 106JSl8n085070; Wed, 6 Jan 2021 19:30:30 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=subject : to : cc : references : from : message-id : date : mime-version : in-reply-to : content-type : content-transfer-encoding; s=corp-2020-01-29; bh=lYqY4R4rCGt7CcD1/khqbNBn6sz24a509rvrObgWS+A=; b=Dg4Iin60anhc9VgLpxCM4XDI+eucaWctPxKpeR6xHqbLwlI4digrKKbQk5HGM2+iS0iX f6x/gCi6VofvrXnuqBcNTvJKz4vp4W17k59ir0oORtuc6uWHFnC0ZtepOXhFalZO6v1X 6bu6w0sDPzZ71z9oZxtUfFZOuagwVLp6pvNrPSAL0AT+WpJI0cy9R40XdT8fvRvYQa2V iiFR6Sd34E1APZvYCfWvzp2B0z9xkgDFFIP3LQYhdFDtcp1ujlkkGAzAZUDnEl7FbDVE VlGnhBMw9taCFaHhtBEhxHJrJqUANpaWCp6PDzbhfOygBLWG8dHQphMYbwNyL2H7nuxk HA== Received: from aserp3020.oracle.com (aserp3020.oracle.com [141.146.126.70]) by aserp2130.oracle.com with ESMTP id 35wcuxsvwu-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Wed, 06 Jan 2021 19:30:30 +0000 Received: from pps.filterd (aserp3020.oracle.com [127.0.0.1]) by aserp3020.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 106JKtBg148451; Wed, 6 Jan 2021 19:30:29 GMT Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by aserp3020.oracle.com with ESMTP id 35v1fa8af9-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 06 Jan 2021 19:30:29 +0000 Received: from abhmp0010.oracle.com (abhmp0010.oracle.com [141.146.116.16]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 106JUQHR020391; Wed, 6 Jan 2021 19:30:27 GMT Received: from [192.168.2.112] (/50.38.35.18) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Wed, 06 Jan 2021 11:30:26 -0800 Subject: Re: [PATCH v2 2/6] mm: hugetlbfs: fix cannot migrate the fallocated HugeTLB page To: Michal Hocko , Muchun Song Cc: akpm@linux-foundation.org, n-horiguchi@ah.jp.nec.com, ak@linux.intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20210106084739.63318-1-songmuchun@bytedance.com> <20210106084739.63318-3-songmuchun@bytedance.com> <20210106163513.GS13207@dhcp22.suse.cz> From: Mike Kravetz Message-ID: <7e69a55c-d501-6b42-8225-a677f09fb829@oracle.com> Date: Wed, 6 Jan 2021 11:30:25 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <20210106163513.GS13207@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9856 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxlogscore=999 phishscore=0 suspectscore=0 spamscore=0 bulkscore=0 adultscore=0 mlxscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2101060108 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9856 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 bulkscore=0 clxscore=1015 spamscore=0 impostorscore=0 priorityscore=1501 mlxscore=0 adultscore=0 mlxlogscore=999 lowpriorityscore=0 phishscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2101060109 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/6/21 8:35 AM, Michal Hocko wrote: > On Wed 06-01-21 16:47:35, Muchun Song wrote: >> Because we only can isolate a active page via isolate_huge_page() >> and hugetlbfs_fallocate() forget to mark it as active, we cannot >> isolate and migrate those pages. > > I've little bit hard time to understand this initially and had to dive > into the code to make sense of it. I would consider the following > wording easier to grasp. Feel free to reuse if you like. > " > If a new hugetlb page is allocated during fallocate it will not be > marked as active (set_page_huge_active) which will result in a later > isolate_huge_page failure when the page migration code would like to > move that page. Such a failure would be unexpected and wrong. > " > > Now to the fix. I believe that this patch shows that the > set_page_huge_active is just too subtle. Is there any reason why we > cannot make all freshly allocated huge pages active by default? I looked into that yesterday. The primary issue is in page fault code, hugetlb_no_page is an example. If page_huge_active is set, then it can be isolated for migration. So, migration could race with the page fault and the page could be migrated before being added to the page table of the faulting task. This was an issue when hugetlb_no_page set_page_huge_active right after allocating and clearing the huge page. Commit cb6acd01e2e4 moved the set_page_huge_active after adding the page to the page table to address this issue. -- Mike Kravetz