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[2003:d8:2f38:ca00:ca3a:83da:653e:234]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b5e8e2747fsm12290788f8f.100.2025.07.14.07.24.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 14 Jul 2025 07:24:23 -0700 (PDT) Message-ID: <3702f6b0-27a9-4ca1-adbd-fb1e2985b2d3@redhat.com> Date: Mon, 14 Jul 2025 16:24:22 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/2] mm/memory_hotplug: fix hwpoisoned large folio handling in do_migrate_range To: Zi Yan , Pankaj Raghav Cc: Matthew Wilcox , Luis Chamberlain , Jinjiang Tu , Oscar Salvador , akpm@linux-foundation.org, linmiaohe@huawei.com, mhocko@kernel.org, linux-mm@kvack.org, wangkefeng.wang@huawei.com References: <20250627125747.3094074-1-tujinjiang@huawei.com> <20250627125747.3094074-3-tujinjiang@huawei.com> <373d02c5-2b62-8543-b786-8fd591ad56eb@huawei.com> <61325284-d1d6-a973-8aa7-c0f226db95fa@huawei.com> <7b2c054b-fc33-4127-aaa9-9edf6a63e142@redhat.com> <924d9d25-e53c-f159-6ec0-e1fd4e96d6e2@huawei.com> <4c5d4fd5-5582-11d8-9fee-24828ac1913d@huawei.com> <8c9719f0-c072-40bb-b7f6-6f2cc41a31dc@redhat.com> <1D589FE5-3515-4ED5-B12E-D5CE23BA5D13@nvidia.com> <641F5B0B-2B48-46FA-AC58-3A8A4BEB1448@nvidia.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 8A15420002 X-Rspam-User: X-Rspamd-Server: rspam09 X-Stat-Signature: d859fkrht55bpszuak9e3zj1mbrpt745 X-HE-Tag: 1752503067-455992 X-HE-Meta: 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 YKp/Gm9d U8pHm2EVmq5ko6+qDL4Jn9NUlOkRIZ3NNjUnKZF3hqu6EbnMnkFVcJj+kRpGYMEvDlwS/bPhTA1CS2EwEj3cXnrIK3Ua9iijGYYP/8X9hTFhjfSlfFPGMJmUDvA== 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: List-Subscribe: List-Unsubscribe: On 14.07.25 16:20, Zi Yan wrote: > On 14 Jul 2025, at 9:53, Pankaj Raghav wrote: > >> Hi Zi Yan, >> >>>> >>>> Probably the WARN_ON can indeed trigger now. >>>> >>>> >>>> @Zi Yan, on a related note ... >>>> >>>> in memory_failure(), we call try_to_split_thp_page(). If it works, >>>> we assume that we have a small folio. >>>> >>>> But that is not the case if split_huge_page() cannot split it to >>>> order-0 ... min_order_for_split(). >>> >>> Right. memory failure needs to learn about this. Either poison every >>> subpage or write back if necessary and drop the page cache folio. >>> >>>> >>>> I'm afraid we havbe more such code that does not expect that if split_huge_page() >>>> succeeds that we still have a large folio ... >>> >>> I did some search, here are the users of split_huge_page*(): >>> >>> 1. ksm: since it is anonymous only, so split always goes to order-0; >>> 2. userfaultfd: it is also anonymous; >>> 3. madvise cold or pageout: a large pagecache folio will be split if it is partially >>> mapped. And it will retry. It might cause a deadlock if the folio has a min order. >>> 4. shmem: split always goes to order-0; >>> 5. memory-failure: see above. >>> >>> So we will need to take care of madvise cold or pageout case? >>> >>> Hi Matthew, Pankaj, and Luis, >>> >>> Is it possible to partially map a min-order folio in a fs with LBS? Based on my >> >> Typically, FSs match the min order with the blocksize of the filesystem. >> As a filesystem block is the smallest unit of data that the filesystem uses >> to store file data on the disk, we cannot partially map them. >> >> So if I understand your question correctly, the answer is no. I'm confused. Shouldn't this be trivially possible? E.g., just mmap() a single page of such a file? Who would make that fail? And if it doesn't fail, who would stop us from munmap()'ing everything except a single page. -- Cheers, David / dhildenb