Messages in this thread | | | Date | Wed, 7 Dec 2022 17:42:23 -0800 | Subject | Re: [PATCH mm-unstable] mm: clarify folio_set_compound_order() zero support | From | Sidhartha Kumar <> |
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On 12/7/22 4:38 PM, John Hubbard wrote: > On 12/7/22 14:37, Sidhartha Kumar wrote: >> Document hugetlb's use of a zero compound order so support for zero >> orders is not removed from folio_set_compound_order(). >> >> Signed-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com> >> Suggested-by: Mike Kravetz <mike.kravetz@oracle.com> >> Suggested-by: Muchun Song <songmuchun@bytedance.com> >> --- >> This can be folded into f2b67a51d0ef6871d4fb0c3e8199f278112bd108 >> mm: add folio dtor and order setter functions >> >> include/linux/mm.h | 7 +++++++ >> 1 file changed, 7 insertions(+) >> >> diff --git a/include/linux/mm.h b/include/linux/mm.h >> index 443d496949a8..cd8508d728f1 100644 >> --- a/include/linux/mm.h >> +++ b/include/linux/mm.h >> @@ -999,9 +999,16 @@ static inline void set_compound_order(struct page >> *page, unsigned int order) >> #endif >> } >> +/* >> + * folio_set_compound_order is generally passed a non-zero order to >> + * initialize a large folio. However, hugetlb code abuses this by >> + * passing in zero when 'dissolving' a large folio. >> + */ > > Wouldn't it be better to instead just create a new function for that > case, such as: > > dissolve_large_folio() >
Prior to the folio conversion, the helper function __destroy_compound_gigantic_page() did:
set_compound_order(page, 0); #ifdef CONFIG_64BIT page[1].compound_nr = 0; #endif
as part of dissolving the page. My goal for this patch was to create a function that would encapsulate that segment of code with a single call of folio_set_compound_order(folio, 0). set_compound_order() does not set compound_nr to 0 when 0 is passed in to the order argument so explicitly setting it is required. I don't think a separate dissolve_large_folio() function for the hugetlb case is needed as __destroy_compound_gigantic_folio() is pretty concise as it is.
> ? > >> static inline void folio_set_compound_order(struct folio *folio, >> unsigned int order) >> { >> + VM_BUG_ON_FOLIO(!folio_test_large(folio), folio); >> + >> folio->_folio_order = order; >> #ifdef CONFIG_64BIT >> folio->_folio_nr_pages = order ? 1U << order : 0; > > thanks,
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