On Thu, Feb 04, 2021 at 11:50:43AM +0800, Muchun Song wrote: > We cannot optimize if a "struct page" crosses page boundaries. If > it is true, we can optimize the code with the help of a compiler. > When free_vmemmap_pages_per_hpage() returns zero, most functions are > optimized by the compiler.
"When the "struct page size" crosses page boundaries we cannot make use of this feature. Let free_vmemmap_pages_per_hpage() return zero if that is the case, most of the functions can be optimized away." I think the above is more clear, but just a suggestion. > Signed-off-by: Muchun Song <[email protected]> Reviewed-by: Oscar Salvador <[email protected]> > --- > include/linux/hugetlb.h | 3 ++- > mm/hugetlb_vmemmap.c | 13 +++++++++++++ > 2 files changed, 15 insertions(+), 1 deletion(-) > > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h > index 822ab2f5542a..7bfb06e16298 100644 > --- a/include/linux/hugetlb.h > +++ b/include/linux/hugetlb.h > @@ -878,7 +878,8 @@ extern bool hugetlb_free_vmemmap_enabled; > > static inline bool is_hugetlb_free_vmemmap_enabled(void) > { > - return hugetlb_free_vmemmap_enabled; > + return hugetlb_free_vmemmap_enabled && > + is_power_of_2(sizeof(struct page)); > } > #else > static inline bool is_hugetlb_free_vmemmap_enabled(void) > diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c > index 8efad9978821..068d0e0cebc8 100644 > --- a/mm/hugetlb_vmemmap.c > +++ b/mm/hugetlb_vmemmap.c > @@ -211,6 +211,12 @@ early_param("hugetlb_free_vmemmap", > early_hugetlb_free_vmemmap_param); > */ > static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h) > { > + /* > + * This check aims to let the compiler help us optimize the code as > + * much as possible. > + */ > + if (!is_power_of_2(sizeof(struct page))) > + return 0; > return h->nr_free_vmemmap_pages; > } > > @@ -280,6 +286,13 @@ void __init hugetlb_vmemmap_init(struct hstate *h) > BUILD_BUG_ON(NR_USED_SUBPAGE >= > RESERVE_VMEMMAP_SIZE / sizeof(struct page)); > > + /* > + * The compiler can help us to optimize this function to null > + * when the size of the struct page is not power of 2. > + */ > + if (!is_power_of_2(sizeof(struct page))) > + return; > + > if (!hugetlb_free_vmemmap_enabled) > return; > > -- > 2.11.0 > > -- Oscar Salvador SUSE L3
