From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with ESMTP id 97BA58D0039 for ; Thu, 17 Feb 2011 17:22:49 -0500 (EST) Date: Thu, 17 Feb 2011 14:22:09 -0800 From: Andrew Morton Subject: Re: [PATCH] mm: vmscan: Stop reclaim/compaction earlier due to insufficient progress if !__GFP_REPEAT Message-Id: <20110217142209.8736cca1.akpm@linux-foundation.org> In-Reply-To: <20110216095048.GA4473@csn.ul.ie> References: <20110209154606.GJ27110@cmpxchg.org> <20110209164656.GA1063@csn.ul.ie> <20110209182846.GN3347@random.random> <20110210102109.GB17873@csn.ul.ie> <20110210124838.GU3347@random.random> <20110210133323.GH17873@csn.ul.ie> <20110210141447.GW3347@random.random> <20110210145813.GK17873@csn.ul.ie> <20110216095048.GA4473@csn.ul.ie> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Johannes Weiner , Andrea Arcangeli , Rik van Riel , Michal Hocko , Kent Overstreet , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Wed, 16 Feb 2011 09:50:49 +0000 Mel Gorman wrote: > should_continue_reclaim() for reclaim/compaction allows scanning to continue > even if pages are not being reclaimed until the full list is scanned. In > terms of allocation success, this makes sense but potentially it introduces > unwanted latency for high-order allocations such as transparent hugepages > and network jumbo frames that would prefer to fail the allocation attempt > and fallback to order-0 pages. Worse, there is a potential that the full > LRU scan will clear all the young bits, distort page aging information and > potentially push pages into swap that would have otherwise remained resident. afaict the patch affects order-0 allocations as well. What are the implications of this? Also, what might be the downsides of this change, and did you test for them? > This patch will stop reclaim/compaction if no pages were reclaimed in the > last SWAP_CLUSTER_MAX pages that were considered. a) Why SWAP_CLUSTER_MAX? Is (SWAP_CLUSTER_MAX+7) better or worse? b) The sentence doesn't seem even vaguely accurate. shrink_zone() will scan vastly more than SWAP_CLUSTER_MAX pages before calling should_continue_reclaim(). Confused. c) The patch doesn't "stop reclaim/compaction" fully. It stops it against one zone. reclaim will then advance on to any other eligible zones. -- 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 internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org