From 7c8ee9a86340db686cd4314e9944dc9b6111bda9 Mon Sep 17 00:00:00 2001 From: Nick Piggin Date: Wed, 22 Mar 2006 00:08:03 -0800 Subject: [PATCH] mm: simplify vmscan vs release refcounting The VM has an interesting race where a page refcount can drop to zero, but it is still on the LRU lists for a short time. This was solved by testing a 0->1 refcount transition when picking up pages from the LRU, and dropping the refcount in that case. Instead, use atomic_add_unless to ensure we never pick up a 0 refcount page from the LRU, thus a 0 refcount page will never have its refcount elevated until it is allocated again. Signed-off-by: Nick Piggin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/mm.h | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-) (limited to 'include/linux') diff --git a/include/linux/mm.h b/include/linux/mm.h index 498ff8778fb..b12d5c76420 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -301,17 +301,20 @@ struct page { * Drop a ref, return true if the logical refcount fell to zero (the page has * no users) */ -#define put_page_testzero(p) \ - ({ \ - BUG_ON(atomic_read(&(p)->_count) == -1);\ - atomic_add_negative(-1, &(p)->_count); \ - }) +static inline int put_page_testzero(struct page *page) +{ + BUG_ON(atomic_read(&page->_count) == -1); + return atomic_add_negative(-1, &page->_count); +} /* - * Grab a ref, return true if the page previously had a logical refcount of - * zero. ie: returns true if we just grabbed an already-deemed-to-be-free page + * Try to grab a ref unless the page has a refcount of zero, return false if + * that is the case. */ -#define get_page_testone(p) atomic_inc_and_test(&(p)->_count) +static inline int get_page_unless_zero(struct page *page) +{ + return atomic_add_unless(&page->_count, 1, -1); +} #define set_page_count(p,v) atomic_set(&(p)->_count, (v) - 1) #define __put_page(p) atomic_dec(&(p)->_count) -- cgit v1.2.3