From b35f1819acd9243a3ff7ad25b1fa8bd6bfe80fb2 Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Tue, 21 Jan 2014 15:49:07 -0800 Subject: mm: create a separate slab for page->ptl allocation If DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC are enabled spinlock_t on x86_64 is 72 bytes. For page->ptl they will be allocated from kmalloc-96 slab, so we loose 24 on each. An average system can easily allocate few tens thousands of page->ptl and overhead is significant. Let's create a separate slab for page->ptl allocation to solve this. To make sure that it really works this time, some numbers from my test machine (just booted, no load): Before: # grep '^\(kmalloc-96\|page->ptl\)' /proc/slabinfo kmalloc-96 31987 32190 128 30 1 : tunables 120 60 8 : slabdata 1073 1073 92 After: # grep '^\(kmalloc-96\|page->ptl\)' /proc/slabinfo page->ptl 27516 28143 72 53 1 : tunables 120 60 8 : slabdata 531 531 9 kmalloc-96 3853 5280 128 30 1 : tunables 120 60 8 : slabdata 176 176 0 Note that the patch is useful not only for debug case, but also for PREEMPT_RT, where spinlock_t is always bloated. Signed-off-by: Kirill A. Shutemov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/mm.h | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'include/linux/mm.h') diff --git a/include/linux/mm.h b/include/linux/mm.h index 58202c26c559..fc4415256ec3 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1350,6 +1350,7 @@ static inline pmd_t *pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long a #if USE_SPLIT_PTE_PTLOCKS #if ALLOC_SPLIT_PTLOCKS +void __init ptlock_cache_init(void); extern bool ptlock_alloc(struct page *page); extern void ptlock_free(struct page *page); @@ -1358,6 +1359,10 @@ static inline spinlock_t *ptlock_ptr(struct page *page) return page->ptl; } #else /* ALLOC_SPLIT_PTLOCKS */ +static inline void ptlock_cache_init(void) +{ +} + static inline bool ptlock_alloc(struct page *page) { return true; @@ -1410,10 +1415,17 @@ static inline spinlock_t *pte_lockptr(struct mm_struct *mm, pmd_t *pmd) { return &mm->page_table_lock; } +static inline void ptlock_cache_init(void) {} static inline bool ptlock_init(struct page *page) { return true; } static inline void pte_lock_deinit(struct page *page) {} #endif /* USE_SPLIT_PTE_PTLOCKS */ +static inline void pgtable_init(void) +{ + ptlock_cache_init(); + pgtable_cache_init(); +} + static inline bool pgtable_page_ctor(struct page *page) { inc_zone_page_state(page, NR_PAGETABLE); -- cgit v1.2.3-59-g8ed1b