On Mon, 16 Aug 2010 10:42:11 +0100 Mel Gorman <mel@xxxxxxxxx> wrote: > 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 <mel@xxxxxxxxx> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>