On 8 Aug 2023, at 5:01, David Hildenbrand wrote: > On 29.03.23 03:17, Zi Yan wrote: >> From: Zi Yan <ziy@xxxxxxxxxx> >> >> To split a THP to any lower order pages, we need to reform THPs on >> subpages at given order and add page refcount based on the new page >> order. Also we need to reinitialize page_deferred_list after removing >> the page from the split_queue, otherwise a subsequent split will see >> list corruption when checking the page_deferred_list again. >> >> It has many uses, like minimizing the number of pages after >> truncating a huge pagecache page. For anonymous THPs, we can only split >> them to order-0 like before until we add support for any size anonymous >> THPs. >> > > Because I'm currently looking into something that would also not be compatible with order-1 for now: > > You should make it clear that order-1 is not supported, like: > > "mm: thp: split huge page to any lower order pages (except order 1)" > > And clarify in the subject why that is the case. Sure. I will add below to the commit message and the comment of split_huge_page_to_list_to_order(): Order-1 folio is not supported because _deferred_list, which is used by partially mapped folios, is stored in subpage 2 and an order-1 folio only has subpage 0 and 1. -- Best Regards, Yan, Zi
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