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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. Signed-off-by: Muchun Song --- include/linux/hugetlb.h | 3 ++- mm/hugetlb_vmemmap.c | 7 +++++++ mm/hugetlb_vmemmap.h | 5 +++-- 3 files changed, 12 insertions(+), 3 deletions(-) diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index 7295f6b3d55e..adc17765e0e9 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -791,7 +791,8 @@ extern bool hugetlb_free_vmemmap_enabled; =20 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 ad123b760245..987248a004f0 100644 --- a/mm/hugetlb_vmemmap.c +++ b/mm/hugetlb_vmemmap.c @@ -242,6 +242,13 @@ void __init hugetlb_vmemmap_init(struct hstate *h) BUILD_BUG_ON(NR_USED_SUBPAGE >=3D RESERVE_VMEMMAP_SIZE / sizeof(struct page)); =20 + /* + * 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; =20 diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h index 8fd9ae113dbd..e8de41295d4d 100644 --- a/mm/hugetlb_vmemmap.h +++ b/mm/hugetlb_vmemmap.h @@ -17,11 +17,12 @@ void hugetlb_vmemmap_init(struct hstate *h); =20 /* * How many vmemmap pages associated with a HugeTLB page that can be fre= ed - * to the buddy allocator. + * to the buddy allocator. The checking of the is_power_of_2() aims to l= et + * the compiler help us optimize the code as much as possible. */ static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h= ) { - return h->nr_free_vmemmap_pages; + return is_power_of_2(sizeof(struct page)) ? h->nr_free_vmemmap_pages : = 0; } #else static inline void alloc_huge_page_vmemmap(struct hstate *h, struct page= *head) --=20 2.11.0