On 17 Nov 2020, at 16:05, Matthew Wilcox wrote: > On Fri, Nov 13, 2020 at 05:38:01PM -0800, Roman Gushchin wrote: >> On Fri, Nov 13, 2020 at 08:08:58PM -0500, Zi Yan wrote: >>> Matthew recently converted split_page_owner to take nr instead of order.[1] >>> But I am not >>> sure why, since it seems to me that two call sites (__split_huge_page in >>> mm/huge_memory.c and split_page in mm/page_alloc.c) can pass the order >>> information. >> >> Yeah, I'm not sure why too. Maybe Matthew has some input here? >> You can also pass new_nr, but IMO orders look so much better here. > > If only I'd written that information in the changelog ... oh wait, I did! > > mm/page_owner: change split_page_owner to take a count > > The implementation of split_page_owner() prefers a count rather than the > old order of the page. When we support a variable size THP, we won't > have the order at this point, but we will have the number of pages. > So change the interface to what the caller and callee would prefer. There are two callers, split_page in mm/page_alloc.c and __split_huge_page in mm/huge_memory.c. The former has the page order. The latter has the page order information before __split_huge_page_tail is called, so we can do old_order = thp_order(head) instead of nr = thp_nr_page(head) and use old_order. What am I missing there? Thanks. — Best Regards, Yan Zi
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