On Tue, Nov 17, 2020 at 04:12:03PM -0500, Zi Yan wrote: > 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? Sure, we could also do that. But what I wrote was true at the time I wrote it.
