From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nick Piggin Message-Id: <20070412103340.5564.23286.sendpatchset@linux.site> In-Reply-To: <20070412103151.5564.16127.sendpatchset@linux.site> References: <20070412103151.5564.16127.sendpatchset@linux.site> Subject: [rfc] rename page_count for lockless pagecache Date: Thu, 12 Apr 2007 14:46:29 +0200 (CEST) Sender: owner-linux-mm@kvack.org Return-Path: To: Linux Memory Management Cc: Nick Piggin , Andrew Morton List-ID: In order to force an audit of page_count users (which I have already done for in-tree users), and to ensure people think about page_count correctly in future, I propose this (incomplete, RFC) patch to rename page_count. Index: linux-2.6/include/linux/mm.h =================================================================== --- linux-2.6.orig/include/linux/mm.h +++ linux-2.6/include/linux/mm.h @@ -267,13 +267,32 @@ static inline int get_page_unless_zero(s return atomic_inc_not_zero(&page->_count); } -static inline int page_count(struct page *page) +static inline int unstable_page_count(struct page *page) { if (unlikely(PageCompound(page))) page = (struct page *)page_private(page); return atomic_read(&page->_count); } +/* + * Returns true if the page count is zero. The page count is + * actually stable if it is zero. + */ +static inline int page_count_is_zero(struct page *page) +{ + return unstable_page_count(page) == 0; +} + +/* + * Returns true if page count of page is less than or equal to c. + * PageNoNewRefs must be set on page. + */ +static inline int page_count_lessequal(struct page *page, int c) +{ + VM_BUG_ON(!PageNoNewRefs(page)); + return unstable_page_count(page) <= c; +} + static inline void get_page(struct page *page) { if (unlikely(PageCompound(page))) Index: linux-2.6/mm/hugetlb.c =================================================================== --- linux-2.6.orig/mm/hugetlb.c +++ linux-2.6/mm/hugetlb.c @@ -90,7 +90,7 @@ static struct page *dequeue_huge_page(st static void free_huge_page(struct page *page) { - BUG_ON(page_count(page)); + BUG_ON(!page_count_is_zero(page)); INIT_LIST_HEAD(&page->lru); @@ -429,7 +429,7 @@ static int hugetlb_cow(struct mm_struct /* If no-one else is actually using this page, avoid the copy * and just make the page writable */ - avoidcopy = (page_count(old_page) == 1); + avoidcopy = (unstable_page_count(old_page) == 1); if (avoidcopy) { set_huge_ptep_writable(vma, address, ptep); return VM_FAULT_MINOR; Index: linux-2.6/mm/memory.c =================================================================== --- linux-2.6.orig/mm/memory.c +++ linux-2.6/mm/memory.c @@ -1270,7 +1270,7 @@ int vm_insert_page(struct vm_area_struct { if (addr < vma->vm_start || addr >= vma->vm_end) return -EFAULT; - if (!page_count(page)) + if (page_count_is_zero(page)) return -EINVAL; vma->vm_flags |= VM_INSERTPAGE; return insert_page(vma->vm_mm, addr, page, vma->vm_page_prot); Index: linux-2.6/mm/migrate.c =================================================================== --- linux-2.6.orig/mm/migrate.c +++ linux-2.6/mm/migrate.c @@ -298,7 +298,7 @@ static int migrate_page_move_mapping(str if (!mapping) { /* Anonymous page */ - if (page_count(page) != 1) + if (unstable_page_count(page) != 1) return -EAGAIN; return 0; } @@ -309,7 +309,7 @@ static int migrate_page_move_mapping(str pslot = radix_tree_lookup_slot(&mapping->page_tree, page_index(page)); - if (page_count(page) != 2 + !!PagePrivate(page) || + if (!page_count_lessequal(page, 2 + !!PagePrivate(page)) || (struct page *)radix_tree_deref_slot(pslot) != page) { spin_unlock_irq(&mapping->tree_lock); clear_page_nonewrefs(page); @@ -606,7 +606,7 @@ static int unmap_and_move(new_page_t get if (!newpage) return -ENOMEM; - if (page_count(page) == 1) + if (unstable_page_count(page) == 1) /* page was freed from under us. So we are done. */ goto move_newpage; Index: linux-2.6/mm/page_alloc.c =================================================================== --- linux-2.6.orig/mm/page_alloc.c +++ linux-2.6/mm/page_alloc.c @@ -192,7 +192,7 @@ static void bad_page(struct page *page) KERN_EMERG "Backtrace:\n", current->comm, page, (int)(2*sizeof(unsigned long)), (unsigned long)page->flags, page->mapping, - page_mapcount(page), page_count(page)); + page_mapcount(page), unstable_page_count(page)); dump_stack(); page->flags &= ~(1 << PG_lru | 1 << PG_private | @@ -355,7 +355,7 @@ static inline int page_is_buddy(struct p return 0; if (PageBuddy(buddy) && page_order(buddy) == order) { - BUG_ON(page_count(buddy) != 0); + BUG_ON(!page_count_is_zero(buddy)); return 1; } return 0; @@ -427,7 +427,7 @@ static inline int free_pages_check(struc { if (unlikely(page_mapcount(page) | (page->mapping != NULL) | - (page_count(page) != 0) | + (!page_count_is_zero(page)) | (page->flags & ( 1 << PG_lru | 1 << PG_private | @@ -576,7 +576,7 @@ static int prep_new_page(struct page *pa { if (unlikely(page_mapcount(page) | (page->mapping != NULL) | - (page_count(page) != 0) | + (!page_count_is_zero(page)) | (page->flags & ( 1 << PG_lru | 1 << PG_private | @@ -854,7 +854,7 @@ void split_page(struct page *page, unsig int i; VM_BUG_ON(PageCompound(page)); - VM_BUG_ON(!page_count(page)); + VM_BUG_ON(page_count_is_zero(page)); for (i = 1; i < (1 << order); i++) set_page_refcounted(page + i); } Index: linux-2.6/mm/rmap.c =================================================================== --- linux-2.6.orig/mm/rmap.c +++ linux-2.6/mm/rmap.c @@ -586,7 +586,7 @@ void page_remove_rmap(struct page *page, printk (KERN_EMERG "Eeek! page_mapcount(page) went negative! (%d)\n", page_mapcount(page)); printk (KERN_EMERG " page pfn = %lx\n", page_to_pfn(page)); printk (KERN_EMERG " page->flags = %lx\n", page->flags); - printk (KERN_EMERG " page->count = %x\n", page_count(page)); + printk (KERN_EMERG " page->count = %x\n", unstable_page_count(page)); printk (KERN_EMERG " page->mapping = %p\n", page->mapping); print_symbol (KERN_EMERG " vma->vm_ops = %s\n", (unsigned long)vma->vm_ops); if (vma->vm_ops) Index: linux-2.6/mm/swapfile.c =================================================================== --- linux-2.6.orig/mm/swapfile.c +++ linux-2.6/mm/swapfile.c @@ -73,7 +73,7 @@ void swap_unplug_io_fn(struct backing_de * condition and it's harmless. However if it triggers without * swapoff it signals a problem. */ - WARN_ON(page_count(page) <= 1); + WARN_ON(unstable_page_count(page) <= 1); bdi = bdev->bd_inode->i_mapping->backing_dev_info; blk_run_backing_dev(bdi, page); @@ -355,7 +355,7 @@ int remove_exclusive_swap_page(struct pa return 0; if (PageWriteback(page)) return 0; - if (page_count(page) != 2) /* 2: us + cache */ + if (unstable_page_count(page) != 2) /* 2: us + cache */ return 0; entry.val = page_private(page); @@ -366,14 +366,14 @@ int remove_exclusive_swap_page(struct pa /* Is the only swap cache user the cache itself? */ retval = 0; if (p->swap_map[swp_offset(entry)] == 1) { - /* Recheck the page count with the swapcache lock held.. */ - spin_lock_irq(&swapper_space.tree_lock); - if ((page_count(page) == 2) && !PageWriteback(page)) { + /* XXX: BUG_ON(PageWriteback(page)) ?? */ + if ((unstable_page_count(page) == 2) && !PageWriteback(page)) { + spin_lock_irq(&swapper_space.tree_lock); __delete_from_swap_cache(page); + spin_unlock_irq(&swapper_space.tree_lock); SetPageDirty(page); retval = 1; } - spin_unlock_irq(&swapper_space.tree_lock); } spin_unlock(&swap_lock); @@ -412,7 +412,7 @@ void free_swap_and_cache(swp_entry_t ent int one_user; BUG_ON(PagePrivate(page)); - one_user = (page_count(page) == 2); + one_user = (unstable_page_count(page) == 2); /* Only cache user (+us), or swap space full? Free it! */ /* Also recheck PageSwapCache after page is locked (above) */ if (PageSwapCache(page) && !PageWriteback(page) && Index: linux-2.6/mm/vmscan.c =================================================================== --- linux-2.6.orig/mm/vmscan.c +++ linux-2.6/mm/vmscan.c @@ -254,7 +254,7 @@ static inline int page_mapping_inuse(str static inline int is_page_cache_freeable(struct page *page) { - return page_count(page) - !!PagePrivate(page) == 2; + return unstable_page_count(page) - !!PagePrivate(page) == 2; } static int may_write_to_queue(struct backing_dev_info *bdi) -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org