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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. > >> understanding of madvise_cold_or_pageout_pte_range(), it seems that it will try >> to split the folio and expects a order-0 folio after a successful split. >> But splitting a min-order folio is a nop. It could lead to a deadlock in the code. >> Or I just get it wrong? > > Yeah, we have checks to make sure we never split a folio < min-order. > > I hope it answers your question :) Thank you for the explanation. This means madvise cold or pageout case is good. Best Regards, Yan, Zi