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imf11.hostedemail.com; dkim=none; spf=pass (imf11.hostedemail.com: domain of wangkefeng.wang@huawei.com designates 45.249.212.189 as permitted sender) smtp.mailfrom=wangkefeng.wang@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1691632162; a=rsa-sha256; cv=none; b=XVkrgxkvxyW4xbAe11DYtEknWso/BuKg9eSaji+O8sP86jxAvvOzUF+ULCDfhLG3MlWczw aJfLTqR12Vtt+1F4u1ULtXO/NfZxHHLU4NHVvw4ZfkB4B9NMlnoLvG84iYB8anY4U1qyx1 WfnNRyy/U5957g9i0TlovwDwLvTXBKI= Received: from dggpemm100001.china.huawei.com (unknown [172.30.72.57]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4RLqXK0Sj2zkXwR; Thu, 10 Aug 2023 09:46:25 +0800 (CST) Received: from [10.174.177.243] (10.174.177.243) by dggpemm100001.china.huawei.com (7.185.36.93) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.27; Thu, 10 Aug 2023 09:49:15 +0800 Message-ID: <2da95492-079b-43b1-a950-d290984a21c0@huawei.com> Date: Thu, 10 Aug 2023 09:49:14 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/4] mm: migrate: use a folio in add_page_for_migration() Content-Language: en-US To: Mike Kravetz CC: Zi Yan , Naoya Horiguchi , Matthew Wilcox , Andrew Morton , , , Huang Ying , David Hildenbrand References: <001ee9b0-ea25-a896-e3ae-9a9b05a46546@huawei.com> <5BBFF5D3-3416-4C0E-9FDD-655661657D67@nvidia.com> <20230809205316.GA3537@monkey> <20230809224424.GB3537@monkey> From: Kefeng Wang In-Reply-To: <20230809224424.GB3537@monkey> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.243] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To dggpemm100001.china.huawei.com (7.185.36.93) X-CFilter-Loop: Reflected X-Rspamd-Queue-Id: 01E3C40019 X-Rspam-User: X-Stat-Signature: cc69pjkyxu1ocifkbrkjeicoa9zcc7ee X-Rspamd-Server: rspam01 X-HE-Tag: 1691632159-124928 X-HE-Meta: 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 HL38UklU gzSt+R2w1ZyyzxKRLO6yJL4Kcc6tjrneUSPwVm3+bpkpR44QyCgm3XEv6Oo8coN34Yz6a5+uSEF2te4icNSCp5iJRjW01iZmiVmLDWBiUQ+tYoZQZXSbwa9cgDAChD3RQpQGHRGpQoJKoz6enpceYwA0P6UMiZUfUiIfuQ88evoAihWtdvWFIUuTTHxb/erlhPsEbAiehgdO+BhH2vS96MKQ3LKv0EB7BVod+ X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2023/8/10 6:44, Mike Kravetz wrote: > On 08/09/23 13:53, Mike Kravetz wrote: >> On 08/09/23 20:37, Kefeng Wang wrote: >>>> >>>> Cc Mike to help us clarify the expected behavior of hugetlb. >>>> >>>> Hi Mike, what is the expected behavior, if a user tries to use move_pages() >>>> to migrate a non head page of a hugetlb page? >>> >>> Could you give some advise, thanks >>> >> >> Sorry, I was away for a while. >> >> It seems unfortunate that move_pages says the passed user addresses >> should be aligned to page boundaries. However, IIUC this is not checked >> or enforced. Otherwise, passing a hugetlb page should return the same >> error. >> >> One thought would be that hugetlb mappings should behave the same >> non-hugetlb mappings. If passed the address of a hugetlb tail page, align >> the address to a hugetlb boundary and migrate the page. This changes the >> existing behavior. However, it would be hard to imagine anyone depending >> on this. >> >> After taking a closer look at the add_page_for_migration(), it seems to >> just ignore passed tail pages and do nothing for such passed addresses. >> Correct? Or, am I missing something? Perhaps that is behavior we want/ >> need to preserve? > > My mistake, status -EACCES is returned when passing a tail page of a > hugetlb page. > As mentioned in previous mail， before e66f17ff7177 ("mm/hugetlb: take page table lock in follow_huge_pmd()") in v4.0, follow_page() will return NULL on tail page for Huagetlb page, so move_pages() will return -ENOENT errno, but after that commit, -EACCES is returned. Meanwhile, the behavior of THP/HUGETLB is different, the whole THP will be migrated on a tail page, but HUGETLB will return -EACCES(after v4.0) or -ENOENT(before v4.0) on tail page. > Back to the question of 'What is the expected behavior if a tail page is > passed?'. I do not think we have defined an expected behavior. If > anything is 'expected' I would say it is -EACCES as returned today. > My question is, Should we keep seem behavior between HUGETLB and THP, or only change the errno from -EACCES to -ENOENT/-EBUSY. I would like to drop PageHead() check for Hugetlb to keep seem behavior, which will keep seem error code if isolate fail or success on head/tail page. Thanks. > BTW - hugetlb pages not migrated due to passing a tail page does not > seem to contribute to a 'Positive return value' indicating the number of > non-migrated pages.