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 CB6E86B004D for ; Fri, 20 Mar 2009 11:37:06 -0400 (EDT) Date: Fri, 20 Mar 2009 15:37:23 +0000 From: Mel Gorman Subject: Re: [PATCH 00/25] Cleanup and optimise the page allocator V5 Message-ID: <20090320153723.GO24586@csn.ul.ie> References: <1237543392-11797-1-git-send-email-mel@csn.ul.ie> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org To: Christoph Lameter Cc: Linux Memory Management List , KOSAKI Motohiro , Nick Piggin , Linux Kernel Mailing List , Lin Ming , Zhang Yanmin , Peter Zijlstra , Andrew Morton List-ID: On Fri, Mar 20, 2009 at 11:00:42AM -0400, Christoph Lameter wrote: > On Fri, 20 Mar 2009, Mel Gorman wrote: > > > The lock contention on some machines goes up for the the zone->lru_lock > > and zone->lock locks which can regress some workloads even though others on > > the same machine still go faster. For netperf, a lock called slock-AF_INET > > seemed very important although I didn't look too closely other than noting > > contention went up. The zone->lock gets hammered a lot by high order allocs > > and frees coming from SLUB which are not covered by the PCP allocator in > > this patchset. zone->lru_lock goes up is less clear but as it's page cache > > releases but overall contention may be up because CPUs are spending less > > time with interrupts disabled and more time trying to do real work but > > contending on the locks. > > We can tune SLUB to buffer more pages if the lru lock becomes too hot. > hmm, I'm missing something in your reasoning. The contention I saw for zone->lru_lock &zone->lru_lock 37350 [] ____pagevec_lru_add+0x9c/0x172 &zone->lru_lock 55423 [] release_pages+0x10a/0x21b &zone->lru_lock 402 [] activate_page+0x4f/0x147 &zone->lru_lock 6 [] put_page+0x94/0x122 So I just assumed it was LRU pages being taken off and freed that was causing the contention. Can SLUB affect that? Maybe you meant zone->lock and SLUB could tune buffers more to avoid that if that lock was hot. That is one alternative but the later patches proposed an alternative whereby high-order and compound pages could be stored on the PCP lists. Compound only really helps SLUB but high-order also helped stacks, signal handlers and the like so it seemed like a good idea one way or the other. Course, this meant a search of the PCP lists or increasing the size of the PCP structure - swings and roundabouts :/ -- 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/ . Don't email: email@kvack.org