[PATCH] mm: create a separate slab for page->ptl allocation

From: Kirill A. Shutemov
Date: Tue Oct 22 2013 - 07:54:16 EST


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.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
include/linux/mm.h | 8 ++++++++
init/main.c | 2 +-
mm/memory.c | 12 ++++++++++--
3 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 9a4a873b2f..2de5da0a41 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1233,6 +1233,7 @@ static inline pmd_t *pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long a
#endif /* CONFIG_MMU && !__ARCH_HAS_4LEVEL_HACK */

#if USE_SPLIT_PTE_PTLOCKS
+void __init ptlock_cache_init(void);
bool __ptlock_alloc(struct page *page);
void __ptlock_free(struct page *page);
static inline bool ptlock_alloc(struct page *page)
@@ -1285,6 +1286,7 @@ static inline void pte_lock_deinit(struct page *page)
}

#else /* !USE_SPLIT_PTE_PTLOCKS */
+static inline void ptlock_cache_init(void) {}
/*
* We use mm->page_table_lock to guard all pagetable pages of the mm.
*/
@@ -1296,6 +1298,12 @@ 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);
diff --git a/init/main.c b/init/main.c
index af310afbef..c71b505392 100644
--- a/init/main.c
+++ b/init/main.c
@@ -466,7 +466,7 @@ static void __init mm_init(void)
mem_init();
kmem_cache_init();
percpu_init_late();
- pgtable_cache_init();
+ pgtable_init();
vmalloc_init();
}

diff --git a/mm/memory.c b/mm/memory.c
index 7e11f745bc..d7e583e270 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4332,11 +4332,19 @@ void copy_user_huge_page(struct page *dst, struct page *src,
#endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */

#if USE_SPLIT_PTE_PTLOCKS
+struct kmem_cache *page_ptl_cachep;
+void __init ptlock_cache_init(void)
+{
+ if (sizeof(spinlock_t) > sizeof(long))
+ page_ptl_cachep = kmem_cache_create("page->ptl",
+ sizeof(spinlock_t), 0, SLAB_PANIC, NULL);
+}
+
bool __ptlock_alloc(struct page *page)
{
spinlock_t *ptl;

- ptl = kmalloc(sizeof(spinlock_t), GFP_KERNEL);
+ ptl = kmem_cache_alloc(page_ptl_cachep, GFP_KERNEL);
if (!ptl)
return false;
page->ptl = (unsigned long)ptl;
@@ -4346,6 +4354,6 @@ bool __ptlock_alloc(struct page *page)
void __ptlock_free(struct page *page)
{
if (sizeof(spinlock_t) > sizeof(page->ptl))
- kfree((spinlock_t *)page->ptl);
+ kmem_cache_free(page_ptl_cachep, (spinlock_t *)page->ptl);
}
#endif
--
1.8.4.rc3

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