From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with ESMTP id 742196B01F3 for ; Mon, 16 Aug 2010 05:42:17 -0400 (EDT) From: Mel Gorman Subject: [PATCH 1/3] mm: page allocator: Update free page counters after pages are placed on the free list Date: Mon, 16 Aug 2010 10:42:11 +0100 Message-Id: <1281951733-29466-2-git-send-email-mel@csn.ul.ie> In-Reply-To: <1281951733-29466-1-git-send-email-mel@csn.ul.ie> References: <1281951733-29466-1-git-send-email-mel@csn.ul.ie> Sender: owner-linux-mm@kvack.org To: linux-mm@kvack.org Cc: Rik van Riel , Nick Piggin , Johannes Weiner , KAMEZAWA Hiroyuki , KOSAKI Motohiro , Mel Gorman List-ID: When allocating a page, the system uses NR_FREE_PAGES counters to determine if watermarks would remain intact after the allocation was made. This check is made without interrupts disabled or the zone lock held and so is race-prone by nature. Unfortunately, when pages are being freed in batch, the counters are updated before the pages are added on the list. During this window, the counters are misleading as the pages do not exist yet. When under significant pressure on systems with large numbers of CPUs, it's possible for processes to make progress even though they should have been stalled. This is particularly problematic if a number of the processes are using GFP_ATOMIC as the min watermark can be accidentally breached and in extreme cases, the system can livelock. This patch updates the counters after the pages have been added to the list. This makes the allocator more cautious with respect to preserving the watermarks and mitigates livelock possibilities. Signed-off-by: Mel Gorman --- mm/page_alloc.c | 5 +++-- 1 files changed, 3 insertions(+), 2 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 9bd339e..c2407a4 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -588,12 +588,12 @@ static void free_pcppages_bulk(struct zone *zone, int count, { int migratetype = 0; int batch_free = 0; + int freed = count; spin_lock(&zone->lock); zone->all_unreclaimable = 0; zone->pages_scanned = 0; - __mod_zone_page_state(zone, NR_FREE_PAGES, count); while (count) { struct page *page; struct list_head *list; @@ -621,6 +621,7 @@ static void free_pcppages_bulk(struct zone *zone, int count, trace_mm_page_pcpu_drain(page, 0, page_private(page)); } while (--count && --batch_free && !list_empty(list)); } + __mod_zone_page_state(zone, NR_FREE_PAGES, freed); spin_unlock(&zone->lock); } @@ -631,8 +632,8 @@ static void free_one_page(struct zone *zone, struct page *page, int order, zone->all_unreclaimable = 0; zone->pages_scanned = 0; - __mod_zone_page_state(zone, NR_FREE_PAGES, 1 << order); __free_one_page(page, zone, order, migratetype); + __mod_zone_page_state(zone, NR_FREE_PAGES, 1 << order); spin_unlock(&zone->lock); } -- 1.7.1 -- 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