On 2022/9/8 7:35, Andrew Morton wrote: > On Tue, 6 Sep 2022 09:52:23 +0800 Liu Shixin <liushixin2@xxxxxxxxxx> wrote: > >> On 2022/9/6 4:07, Andrew Morton wrote: >>> On Mon, 5 Sep 2022 21:38:13 +0800 Liu Shixin <liushixin2@xxxxxxxxxx> wrote: >>> >>>> If two or more threads call get_huge_zero_page concurrently, THP_ZERO_PAGE_ALLOC >>>> may increased two or more times. But actually, this should only count >>>> as once since the extra zero pages has been freed. >>> Well, for better of for worse, >>> Documentation/admin-guide/mm/transhuge.rst says >>> >>> thp_zero_page_alloc >>> is incremented every time a huge zero page is >>> successfully allocated. It includes allocations which where >>> dropped due race with other allocation. Note, it doesn't count >>> every map of the huge zero page, only its allocation. >>> >>> If you think this interprtation should be changed then please explain >>> why, and let's be sure to update the documentation accordingly. >>> >>> . >> Thanks for your explanation. I misunderstood the meaning of thp_zero_page_alloc before. >> Although the rules are clearly explained in the documentation, I think that this variable >> should only incremented when a huge zero page used for thp is successfully allocated and >> the pages dropped due race should skip increment. It seems strange to count in all allocations. >> >> If there's something I still misunderstand, please point it out, thanks. > It seems strange to me also. Perhaps there's a rationale buried in the > git and mailing list history. > > . I didn't find previous discussion about this point. I update document in v2. Kirill, what do you think about this change? https://lore.kernel.org/linux-mm/20220908035533.2186159-1-liushixin2@xxxxxxxxxx/
