From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with ESMTP id 640BE6B0047 for ; Tue, 9 Mar 2010 12:30:21 -0500 (EST) Date: Tue, 9 Mar 2010 17:30:03 +0000 From: Mel Gorman Subject: Re: [PATCH 1/3] page-allocator: Under memory pressure, wait on pressure to relieve instead of congestion Message-ID: <20100309173003.GH4883@csn.ul.ie> References: <1268048904-19397-1-git-send-email-mel@csn.ul.ie> <1268048904-19397-2-git-send-email-mel@csn.ul.ie> <4B966F93.9060207@linux.vnet.ibm.com> <20100309170123.GG4883@csn.ul.ie> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org To: Christoph Lameter Cc: Christian Ehrhardt , linux-mm@kvack.org, Nick Piggin , Chris Mason , Jens Axboe , linux-kernel@vger.kernel.org List-ID: On Tue, Mar 09, 2010 at 11:11:55AM -0600, Christoph Lameter wrote: > On Tue, 9 Mar 2010, Mel Gorman wrote: > > > Until it's timeout at least. It's still better than the current > > situation of sleeping on congestion. > > Congestion may clear if memory becomes available in other zones. > I understand that. > > The ideal would be waiting on a per-node basis. I'm just not liking having > > to look up the node structure when freeing a patch of pages and making a > > cache line in there unnecessarily hot. > > The node structure (pgdat) contains the zone structures. If you know the > type of zone then you can calculate the pgdat address. > I know you can lookup the pgdat from the zone structure. The concern is that the suggestion requires adding fields to the node structure that then become hot in the free_page path when the per-cpu lists are being drained. This patch also adds a hot cache line to the zone but at least it can be eliminated by using zone->flags. The same optimisation does not apply to working on a per-node basis. Adding such a hot line is a big minus and the gain is that processes may wake up slightly faster when under memory pressure. It's not a good trade-off. > > > But then an overallocated node may stall processes. If that node is full > > > of unreclaimable memory then the process may never wake up? > > > > Processes wake after a timeout. > > Ok that limits it but still we may be waiting for no reason. > -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- 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