From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with SMTP id D3ED16B009A for ; Thu, 26 Nov 2009 08:09:03 -0500 (EST) Subject: Re: [PATCH-RFC] cfq: Disable low_latency by default for 2.6.32 From: Mike Galbraith In-Reply-To: <20091126121945.GB13095@csn.ul.ie> References: <20091126121945.GB13095@csn.ul.ie> Content-Type: text/plain Date: Thu, 26 Nov 2009 14:08:57 +0100 Message-Id: <1259240937.7371.15.camel@marge.simson.net> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Mel Gorman Cc: Jens Axboe , Andrew Morton , Linus Torvalds , Frans Pop , Jiri Kosina , Sven Geggus , Karol Lewandowski , Tobias Oetiker , KOSAKI Motohiro , Pekka Enberg , Rik van Riel , Christoph Lameter , Stephan von Krawczynski , "Rafael J. Wysocki" , linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: On Thu, 2009-11-26 at 12:19 +0000, Mel Gorman wrote: > (cc'ing the people from the page allocator failure thread as this might be > relevant to some of their problems) > > I know this is very last minute but I believe we should consider disabling > the "low_latency" tunable for block devices by default for 2.6.32. There was > evidence that low_latency was a problem last week for page allocation failure > reports but the reproduction-case was unusual and involved high-order atomic > allocations in low-memory conditions. It took another few days to accurately > show the problem for more normal workloads and it's a bit more wide-spread > than just allocation failures. > > Basically, low_latency looks great as long as you have plenty of memory > but in low memory situations, it appears to cause problems that manifest > as reduced performance, desktop stalls and in some cases, page allocation > failures. I think most kernel developers are not seeing the problem as they > tend to test on beefier machines and without hitting swap or low-memory > situations for the most part. When they are hitting low-memory situations, > it tends to be for stress tests where stalls and low performance are expected. Ouch. It was bad desktop stalls under heavy write that kicked the whole thing off. -Mike -- 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