From 4c21e2f2441dc5fbb957b030333f5a3f2d02dea7 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Sat, 29 Oct 2005 18:16:40 -0700 Subject: [PATCH] mm: split page table lock Christoph Lameter demonstrated very poor scalability on the SGI 512-way, with a many-threaded application which concurrently initializes different parts of a large anonymous area. This patch corrects that, by using a separate spinlock per page table page, to guard the page table entries in that page, instead of using the mm's single page_table_lock. (But even then, page_table_lock is still used to guard page table allocation, and anon_vma allocation.) In this implementation, the spinlock is tucked inside the struct page of the page table page: with a BUILD_BUG_ON in case it overflows - which it would in the case of 32-bit PA-RISC with spinlock debugging enabled. Splitting the lock is not quite for free: another cacheline access. Ideally, I suppose we would use split ptlock only for multi-threaded processes on multi-cpu machines; but deciding that dynamically would have its own costs. So for now enable it by config, at some number of cpus - since the Kconfig language doesn't support inequalities, let preprocessor compare that with NR_CPUS. But I don't think it's worth being user-configurable: for good testing of both split and unsplit configs, split now at 4 cpus, and perhaps change that to 8 later. There is a benefit even for singly threaded processes: kswapd can be attacking one part of the mm while another part is busy faulting. Signed-off-by: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/buffer_head.h | 6 +++--- include/linux/mm.h | 46 +++++++++++++++++++++++++++++++++++++-------- 2 files changed, 41 insertions(+), 11 deletions(-) (limited to 'include') diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h index 88af42f5e04..c937d6e6550 100644 --- a/include/linux/buffer_head.h +++ b/include/linux/buffer_head.h @@ -126,8 +126,8 @@ BUFFER_FNS(Eopnotsupp, eopnotsupp) /* If we *know* page->private refers to buffer_heads */ #define page_buffers(page) \ ({ \ - BUG_ON(!PagePrivate(page)); \ - ((struct buffer_head *)(page)->private); \ + BUG_ON(!PagePrivate(page)); \ + ((struct buffer_head *)page_private(page)); \ }) #define page_has_buffers(page) PagePrivate(page) @@ -219,7 +219,7 @@ static inline void attach_page_buffers(struct page *page, { page_cache_get(page); SetPagePrivate(page); - page->private = (unsigned long)head; + set_page_private(page, (unsigned long)head); } static inline void get_bh(struct buffer_head *bh) diff --git a/include/linux/mm.h b/include/linux/mm.h index e8d1424153b..8a514eca40d 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -226,13 +226,18 @@ struct page { * to show when page is mapped * & limit reverse map searches. */ - unsigned long private; /* Mapping-private opaque data: + union { + unsigned long private; /* Mapping-private opaque data: * usually used for buffer_heads * if PagePrivate set; used for * swp_entry_t if PageSwapCache * When page is free, this indicates * order in the buddy system. */ +#if NR_CPUS >= CONFIG_SPLIT_PTLOCK_CPUS + spinlock_t ptl; +#endif + } u; struct address_space *mapping; /* If low bit clear, points to * inode address_space, or NULL. * If page mapped as anonymous @@ -260,6 +265,9 @@ struct page { #endif /* WANT_PAGE_VIRTUAL */ }; +#define page_private(page) ((page)->u.private) +#define set_page_private(page, v) ((page)->u.private = (v)) + /* * FIXME: take this include out, include page-flags.h in * files which need it (119 of them) @@ -311,17 +319,17 @@ extern void FASTCALL(__page_cache_release(struct page *)); #ifdef CONFIG_HUGETLB_PAGE -static inline int page_count(struct page *p) +static inline int page_count(struct page *page) { - if (PageCompound(p)) - p = (struct page *)p->private; - return atomic_read(&(p)->_count) + 1; + if (PageCompound(page)) + page = (struct page *)page_private(page); + return atomic_read(&page->_count) + 1; } static inline void get_page(struct page *page) { if (unlikely(PageCompound(page))) - page = (struct page *)page->private; + page = (struct page *)page_private(page); atomic_inc(&page->_count); } @@ -587,7 +595,7 @@ static inline int PageAnon(struct page *page) static inline pgoff_t page_index(struct page *page) { if (unlikely(PageSwapCache(page))) - return page->private; + return page_private(page); return page->index; } @@ -779,9 +787,31 @@ static inline pmd_t *pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long a } #endif /* CONFIG_MMU && !__ARCH_HAS_4LEVEL_HACK */ +#if NR_CPUS >= CONFIG_SPLIT_PTLOCK_CPUS +/* + * We tuck a spinlock to guard each pagetable page into its struct page, + * at page->private, with BUILD_BUG_ON to make sure that this will not + * overflow into the next struct page (as it might with DEBUG_SPINLOCK). + * When freeing, reset page->mapping so free_pages_check won't complain. + */ +#define __pte_lockptr(page) &((page)->u.ptl) +#define pte_lock_init(_page) do { \ + spin_lock_init(__pte_lockptr(_page)); \ +} while (0) +#define pte_lock_deinit(page) ((page)->mapping = NULL) +#define pte_lockptr(mm, pmd) ({(void)(mm); __pte_lockptr(pmd_page(*(pmd)));}) +#else +/* + * We use mm->page_table_lock to guard all pagetable pages of the mm. + */ +#define pte_lock_init(page) do {} while (0) +#define pte_lock_deinit(page) do {} while (0) +#define pte_lockptr(mm, pmd) ({(void)(pmd); &(mm)->page_table_lock;}) +#endif /* NR_CPUS < CONFIG_SPLIT_PTLOCK_CPUS */ + #define pte_offset_map_lock(mm, pmd, address, ptlp) \ ({ \ - spinlock_t *__ptl = &(mm)->page_table_lock; \ + spinlock_t *__ptl = pte_lockptr(mm, pmd); \ pte_t *__pte = pte_offset_map(pmd, address); \ *(ptlp) = __ptl; \ spin_lock(__ptl); \ -- cgit v1.2.3