From 62906027091f1d02de44041524f0769f60bb9cf3 Mon Sep 17 00:00:00 2001 From: Nicholas Piggin Date: Sun, 25 Dec 2016 13:00:30 +1000 Subject: mm: add PageWaiters indicating tasks are waiting for a page bit Add a new page flag, PageWaiters, to indicate the page waitqueue has tasks waiting. This can be tested rather than testing waitqueue_active which requires another cacheline load. This bit is always set when the page has tasks on page_waitqueue(page), and is set and cleared under the waitqueue lock. It may be set when there are no tasks on the waitqueue, which will cause a harmless extra wakeup check that will clears the bit. The generic bit-waitqueue infrastructure is no longer used for pages. Instead, waitqueues are used directly with a custom key type. The generic code was not flexible enough to have PageWaiters manipulation under the waitqueue lock (which simplifies concurrency). This improves the performance of page lock intensive microbenchmarks by 2-3%. Putting two bits in the same word opens the opportunity to remove the memory barrier between clearing the lock bit and testing the waiters bit, after some work on the arch primitives (e.g., ensuring memory operand widths match and cover both bits). Signed-off-by: Nicholas Piggin Cc: Dave Hansen Cc: Bob Peterson Cc: Steven Whitehouse Cc: Andrew Lutomirski Cc: Andreas Gruenbacher Cc: Peter Zijlstra Cc: Mel Gorman Signed-off-by: Linus Torvalds --- mm/swap.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'mm/swap.c') diff --git a/mm/swap.c b/mm/swap.c index 4dcf852e1e6d..844baedd2429 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -69,6 +69,7 @@ static void __page_cache_release(struct page *page) del_page_from_lru_list(page, lruvec, page_off_lru(page)); spin_unlock_irqrestore(zone_lru_lock(zone), flags); } + __ClearPageWaiters(page); mem_cgroup_uncharge(page); } @@ -784,6 +785,7 @@ void release_pages(struct page **pages, int nr, bool cold) /* Clear Active bit in case of parallel mark_page_accessed */ __ClearPageActive(page); + __ClearPageWaiters(page); list_add(&page->lru, &pages_to_free); } -- cgit v1.2.3-59-g8ed1b