Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757511AbZCPQmv (ORCPT ); Mon, 16 Mar 2009 12:42:51 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752463AbZCPQmm (ORCPT ); Mon, 16 Mar 2009 12:42:42 -0400 Received: from gir.skynet.ie ([193.1.99.77]:44963 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752014AbZCPQml (ORCPT ); Mon, 16 Mar 2009 12:42:41 -0400 Date: Mon, 16 Mar 2009 16:42:39 +0000 From: Mel Gorman To: Christoph Lameter Cc: Linux Memory Management List , Pekka Enberg , Rik van Riel , KOSAKI Motohiro , Johannes Weiner , Nick Piggin , Linux Kernel Mailing List , Lin Ming , Zhang Yanmin , Peter Zijlstra Subject: Re: [PATCH 23/35] Update NR_FREE_PAGES only as necessary Message-ID: <20090316164238.GK24293@csn.ul.ie> References: <1237196790-7268-1-git-send-email-mel@csn.ul.ie> <1237196790-7268-24-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: User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1650 Lines: 43 On Mon, Mar 16, 2009 at 12:17:15PM -0400, Christoph Lameter wrote: > On Mon, 16 Mar 2009, Mel Gorman wrote: > > > When pages are being freed to the buddy allocator, the zone > > NR_FREE_PAGES counter must be updated. In the case of bulk per-cpu page > > freeing, it's updated once per page. This retouches cache lines more > > than necessary. Update the counters one per per-cpu bulk free. > > Not sure about the reasoning here since the individual updates are batched Each update take places between lots of other work with different cache lines. With enough buddy merging, I believed the line holding the counters could at least get pushed out of L1 although probably not L2 cache. > and you are touching the same cacheline as the pcp you are operating on > and have to touch anyways. > > But if its frequent that __rmqueue_smallest() and free_pages_bulk() are > called with multiple pages then its always a win. > It's frequent enough that it showed up in profiles > Reviewed-by: Christoph Lameter > > > + __mod_zone_page_state(zone, NR_FREE_PAGES, -(1UL << order) * i); > > A multiplication? Okay with contemporary cpus I guess. > Replaced with __mod_zone_page_state(zone, NR_FREE_PAGES, -(i << order)); -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/