From: Muchun Song <songmuchun@xxxxxxxxxxxxx> Subject: mm: hugetlb: replace hugetlb_free_vmemmap_enabled with a static_key The page_fixed_fake_head() is used throughout memory management and the conditional check requires checking a global variable, although the overhead of this check may be small, it increases when the memory cache comes under pressure. Also, the global variable will not be modified after system boot, so it is very appropriate to use static key machanism. Link: https://lkml.kernel.org/r/20211101031651.75851-3-songmuchun@xxxxxxxxxxxxx Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx> Reviewed-by: Barry Song <song.bao.hua@xxxxxxxxxxxxx> Cc: Bodeddula Balasubramaniam <bodeddub@xxxxxxxxxx> Cc: Chen Huang <chenhuang5@xxxxxxxxxx> Cc: David Hildenbrand <david@xxxxxxxxxx> Cc: Fam Zheng <fam.zheng@xxxxxxxxxxxxx> Cc: Jonathan Corbet <corbet@xxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Cc: Oscar Salvador <osalvador@xxxxxxx> Cc: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx> Cc: Xiongchun Duan <duanxiongchun@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/hugetlb.h | 6 ------ include/linux/page-flags.h | 16 ++++++++++++++-- mm/hugetlb_vmemmap.c | 12 ++++++------ mm/memory_hotplug.c | 2 +- 4 files changed, 21 insertions(+), 15 deletions(-) --- a/include/linux/hugetlb.h~mm-hugetlb-replace-hugetlb_free_vmemmap_enabled-with-a-static_key +++ a/include/linux/hugetlb.h @@ -1075,12 +1075,6 @@ static inline void set_huge_swap_pte_at( } #endif /* CONFIG_HUGETLB_PAGE */ -#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP -extern bool hugetlb_free_vmemmap_enabled; -#else -#define hugetlb_free_vmemmap_enabled false -#endif - static inline spinlock_t *huge_pte_lock(struct hstate *h, struct mm_struct *mm, pte_t *pte) { --- a/include/linux/page-flags.h~mm-hugetlb-replace-hugetlb_free_vmemmap_enabled-with-a-static_key +++ a/include/linux/page-flags.h @@ -191,7 +191,14 @@ enum pageflags { #ifndef __GENERATING_BOUNDS_H #ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP -extern bool hugetlb_free_vmemmap_enabled; +DECLARE_STATIC_KEY_MAYBE(CONFIG_HUGETLB_PAGE_FREE_VMEMMAP_DEFAULT_ON, + hugetlb_free_vmemmap_enabled_key); + +static __always_inline bool hugetlb_free_vmemmap_enabled(void) +{ + return static_branch_maybe(CONFIG_HUGETLB_PAGE_FREE_VMEMMAP_DEFAULT_ON, + &hugetlb_free_vmemmap_enabled_key); +} /* * If the feature of freeing some vmemmap pages associated with each HugeTLB @@ -211,7 +218,7 @@ extern bool hugetlb_free_vmemmap_enabled */ static __always_inline const struct page *page_fixed_fake_head(const struct page *page) { - if (!hugetlb_free_vmemmap_enabled) + if (!hugetlb_free_vmemmap_enabled()) return page; /* @@ -239,6 +246,11 @@ static inline const struct page *page_fi { return page; } + +static inline bool hugetlb_free_vmemmap_enabled(void) +{ + return false; +} #endif static __always_inline int page_is_fake_head(struct page *page) --- a/mm/hugetlb_vmemmap.c~mm-hugetlb-replace-hugetlb_free_vmemmap_enabled-with-a-static_key +++ a/mm/hugetlb_vmemmap.c @@ -188,9 +188,9 @@ #define RESERVE_VMEMMAP_NR 1U #define RESERVE_VMEMMAP_SIZE (RESERVE_VMEMMAP_NR << PAGE_SHIFT) -bool hugetlb_free_vmemmap_enabled __read_mostly = - IS_ENABLED(CONFIG_HUGETLB_PAGE_FREE_VMEMMAP_DEFAULT_ON); -EXPORT_SYMBOL(hugetlb_free_vmemmap_enabled); +DEFINE_STATIC_KEY_MAYBE(CONFIG_HUGETLB_PAGE_FREE_VMEMMAP_DEFAULT_ON, + hugetlb_free_vmemmap_enabled_key); +EXPORT_SYMBOL(hugetlb_free_vmemmap_enabled_key); static int __init early_hugetlb_free_vmemmap_param(char *buf) { @@ -204,9 +204,9 @@ static int __init early_hugetlb_free_vme return -EINVAL; if (!strcmp(buf, "on")) - hugetlb_free_vmemmap_enabled = true; + static_branch_enable(&hugetlb_free_vmemmap_enabled_key); else if (!strcmp(buf, "off")) - hugetlb_free_vmemmap_enabled = false; + static_branch_disable(&hugetlb_free_vmemmap_enabled_key); else return -EINVAL; @@ -284,7 +284,7 @@ void __init hugetlb_vmemmap_init(struct BUILD_BUG_ON(__NR_USED_SUBPAGE >= RESERVE_VMEMMAP_SIZE / sizeof(struct page)); - if (!hugetlb_free_vmemmap_enabled) + if (!hugetlb_free_vmemmap_enabled()) return; vmemmap_pages = (nr_pages * sizeof(struct page)) >> PAGE_SHIFT; --- a/mm/memory_hotplug.c~mm-hugetlb-replace-hugetlb_free_vmemmap_enabled-with-a-static_key +++ a/mm/memory_hotplug.c @@ -1327,7 +1327,7 @@ bool mhp_supports_memmap_on_memory(unsig * populate a single PMD. */ return memmap_on_memory && - !hugetlb_free_vmemmap_enabled && + !hugetlb_free_vmemmap_enabled() && IS_ENABLED(CONFIG_MHP_MEMMAP_ON_MEMORY) && size == memory_block_size_bytes() && IS_ALIGNED(vmemmap_size, PMD_SIZE) && _
