From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with ESMTP id 9C83A6B008A for ; Tue, 14 Dec 2010 17:34:38 -0500 (EST) Date: Tue, 14 Dec 2010 14:33:06 -0800 From: Andrew Morton Subject: Re: [PATCH 1/6] mm: kswapd: Stop high-order balancing when any suitable zone is balanced Message-Id: <20101214143306.485f2c7c.akpm@linux-foundation.org> In-Reply-To: <1291995985-5913-2-git-send-email-mel@csn.ul.ie> References: <1291995985-5913-1-git-send-email-mel@csn.ul.ie> <1291995985-5913-2-git-send-email-mel@csn.ul.ie> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Mel Gorman Cc: Simon Kirby , KOSAKI Motohiro , Shaohua Li , Dave Hansen , Johannes Weiner , linux-mm , linux-kernel List-ID: On Fri, 10 Dec 2010 15:46:20 +0000 Mel Gorman wrote: > When the allocator enters its slow path, kswapd is woken up to balance the > node. It continues working until all zones within the node are balanced. For > order-0 allocations, this makes perfect sense but for higher orders it can > have unintended side-effects. If the zone sizes are imbalanced, kswapd may > reclaim heavily within a smaller zone discarding an excessive number of > pages. Why was it doing this? > The user-visible behaviour is that kswapd is awake and reclaiming > even though plenty of pages are free from a suitable zone. Suitable for what? I assume you refer to a future allocation which can be satisfied from more than one of the zones? But what if that allocation wanted to allocate a high-order page from a zone which we just abandoned? > This patch alters the "balance" logic for high-order reclaim allowing kswapd > to stop if any suitable zone becomes balanced to reduce the number of pages again, suitable for what? > it reclaims from other zones. kswapd still tries to ensure that order-0 > watermarks for all zones are met before sleeping. Handling order-0 pages differently from higher-order pages sounds weird and wrong. I don't think I understand this patch. -- 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/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org