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 SMTP id 199B46B004A for ; Wed, 29 Sep 2010 10:34:13 -0400 (EDT) Date: Wed, 29 Sep 2010 09:34:09 -0500 (CDT) From: Christoph Lameter Subject: Re: zone state overhead In-Reply-To: <20100929141730.GB14204@csn.ul.ie> Message-ID: References: <20100928050801.GA29021@sli10-conroe.sh.intel.com> <20100928133059.GL8187@csn.ul.ie> <20100929100307.GA14204@csn.ul.ie> <20100929141730.GB14204@csn.ul.ie> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org To: Mel Gorman Cc: David Rientjes , Shaohua Li , linux-mm@kvack.org List-ID: On Wed, 29 Sep 2010, Mel Gorman wrote: > > Updating the threshold also is expensive. > > Even if it's moved to a read-mostly part of the zone such as after > lowmem_reserve? The threshold is stored in the hot part of the per cpu page structure. > > I thought more along the lines > > of reducing the threshold for good if the VM runs into reclaim trouble > > because of too high fuzziness in the counters. > > > > That would be unfortunate as it would only take trouble to happen once > for performance to be impaired for the remaining uptime of the machine. Reclaim also impairs performance and inaccurate counters may cause unnecessary reclaim. Ultimately this is a tradeoff. The current thresholds were calculated so that there will be zero impact even for very large configurations where all processors continual page fault. I think we have some leeway to go lower there. The tuning situation was a bit extreme. -- 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