From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with ESMTP id 6B92A6B004A for ; Thu, 18 Nov 2010 03:13:11 -0500 (EST) Date: Thu, 18 Nov 2010 08:12:54 +0000 From: Mel Gorman Subject: Re: [PATCH 0/8] Use memory compaction instead of lumpy reclaim during high-order allocations Message-ID: <20101118081254.GB8135@csn.ul.ie> References: <1290010969-26721-1-git-send-email-mel@csn.ul.ie> <20101117154641.51fd7ce5.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20101117154641.51fd7ce5.akpm@linux-foundation.org> Sender: owner-linux-mm@kvack.org To: Andrew Morton Cc: Andrea Arcangeli , KOSAKI Motohiro , Rik van Riel , Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: On Wed, Nov 17, 2010 at 03:46:41PM -0800, Andrew Morton wrote: > On Wed, 17 Nov 2010 16:22:41 +0000 > Mel Gorman wrote: > > > Huge page allocations are not expected to be cheap but lumpy reclaim > > is still very disruptive. > > Huge pages are boring. Can we expect any benefit for the > stupid-nic-driver-which-does-order-4-GFP_ATOMIC-allocations problem? > Yes. Specifically, while GFP_ATOMIC allocations still cannot enter compaction (although with asynchronous migration, it's closer), kswapd will react faster. As a result, it should be harder to trigger allocation failures. Huge pages are simply the worst case in terms of allocation latency which is why I tend to focus testing on them. That, and I don't have a suitable pair of machines with one of these order-4-atomic-stupid-nics. > > I haven't pushed hard on the concept of lumpy compaction yet and right > > now I don't intend to during this cycle. The initial prototypes did not > > behave as well as expected and this series improves the current situation > > a lot without introducing new algorithms. Hence, I'd like this series to > > be considered for merging. > > Translation: "Andrew, wait for the next version"? :) > Preferably do not wait unless review reveals a major flaw. Lumpy compaction in its initial prototype versions simply did not work out as a good policy modification and requires much deeper thought. This series was effective at getting latencies down to the level I expected lumpy compaction to. If I do make lumpy compaction work properly, its effect will be to reduce scanning rates but the latencies are likely to be similar. > > I'm hoping that this series also removes the > > necessity for the "delete lumpy reclaim" patch from the THP tree. > > Now I'm sad. I read all that and was thinking "oh goody, we get to > delete something for once". But no :( > > If you can get this stuff to work nicely, why can't we remove lumpy > reclaim? Ultimately we should be able to. Lumpy reclaim is still there for the !CONFIG_COMPACTION case and to have an option if we find that compaction behaves badly for some 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/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org