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 691B4C433DB for ; Wed, 6 Jan 2021 21:09:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3DBDD2313C for ; Wed, 6 Jan 2021 21:09:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726171AbhAFVJf (ORCPT ); Wed, 6 Jan 2021 16:09:35 -0500 Received: from aserp2130.oracle.com ([141.146.126.79]:53376 "EHLO aserp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725951AbhAFVJe (ORCPT ); Wed, 6 Jan 2021 16:09:34 -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 106L4miC100728; Wed, 6 Jan 2021 21:07:44 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=W6W0gJfOIiS/xI8E4K2OEUfCxl6zQ9m2UdSjovBPjRc=; b=hChs4iZNT6WJlzEukQaa10Jor2WBU+1DGrqP/MK15J5eTgiJlkspQhPH+iq31emYCQlq 7Ct+UgCdbAl52xXQ8EiXZCWlJ1tmITUZkiNfsOXOPj+pkP7k5IjtT36M8tXGoLWxalDJ H9nfxM984yiFIZ3kl3RqTgjtaPFv5U/E1CiB5BRXSjCiDsAJ0d9hEyepyHssvftLj8l9 Uz3wJxYNLjhlvq12O71J0RK3TX2qMjdt3T8M3j86hZLdIWNm6gqzETJt5SBRyuw0IS/0 6Gusq9Odpmc2rPwCsN1dSd+ymlwGd795oWluC1an8HoungdSY47OFrUZtpq296gH5sAf LQ== Received: from userp3030.oracle.com (userp3030.oracle.com [156.151.31.80]) by aserp2130.oracle.com with ESMTP id 35wcuxt8ug-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Wed, 06 Jan 2021 21:07:44 +0000 Received: from pps.filterd (userp3030.oracle.com [127.0.0.1]) by userp3030.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 106L5Pjt023332; Wed, 6 Jan 2021 21:07:43 GMT Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by userp3030.oracle.com with ESMTP id 35w3g1k52p-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 06 Jan 2021 21:07:43 +0000 Received: from abhmp0010.oracle.com (abhmp0010.oracle.com [141.146.116.16]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id 106L7fJg011347; Wed, 6 Jan 2021 21:07:41 GMT Received: from [192.168.2.112] (/50.38.35.18) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Wed, 06 Jan 2021 13:07:41 -0800 Subject: Re: [PATCH v2 2/6] mm: hugetlbfs: fix cannot migrate the fallocated HugeTLB page To: Michal Hocko Cc: Muchun Song , 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> <7e69a55c-d501-6b42-8225-a677f09fb829@oracle.com> <20210106200242.GY13207@dhcp22.suse.cz> From: Mike Kravetz Message-ID: Date: Wed, 6 Jan 2021 13:07:40 -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: <20210106200242.GY13207@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 mlxscore=0 malwarescore=0 adultscore=0 phishscore=0 spamscore=0 mlxlogscore=999 suspectscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2101060121 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-2101060121 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/6/21 12:02 PM, Michal Hocko wrote: > On Wed 06-01-21 11:30:25, Mike Kravetz wrote: >> 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. > > Thanks for the clarification. I was not aware of this subtlety. The > existing comment is not helping much TBH. I am still digesting the > suggested race. The page is new and exclusive and not visible via page > tables yet, so the only source of the migration would be pfn based > (hotplug, poisoning), right? That is correct. > Btw. s@set_page_huge_active@set_page_huge_migrateable@ would help > readability IMHO. With a comment explaining that this _has_ to be called > after the page is fully initialized. Agree, I will add that as a future enhancement. -- Mike Kravetz