From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752360Ab3LQLN5 (ORCPT ); Tue, 17 Dec 2013 06:13:57 -0500 Received: from cantor2.suse.de ([195.135.220.15]:52170 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751001Ab3LQLN4 (ORCPT ); Tue, 17 Dec 2013 06:13:56 -0500 Date: Tue, 17 Dec 2013 11:13:52 +0000 From: Mel Gorman To: Johannes Weiner Cc: Andrew Morton , Dave Hansen , Rik van Riel , Linux-MM , LKML Subject: Re: [PATCH 3/7] mm: page_alloc: Use zone node IDs to approximate locality Message-ID: <20131217111352.GZ11295@suse.de> References: <1386943807-29601-1-git-send-email-mgorman@suse.de> <1386943807-29601-4-git-send-email-mgorman@suse.de> <20131216202507.GZ21724@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20131216202507.GZ21724@cmpxchg.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 16, 2013 at 03:25:07PM -0500, Johannes Weiner wrote: > On Fri, Dec 13, 2013 at 02:10:03PM +0000, Mel Gorman wrote: > > zone_local is using node_distance which is a more expensive call than > > necessary. On x86, it's another function call in the allocator fast path > > and increases cache footprint. This patch makes the assumption zones on a > > local node will share the same node ID. The necessary information should > > already be cache hot. > > > > Signed-off-by: Mel Gorman > > --- > > mm/page_alloc.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 64020eb..fd9677e 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -1816,7 +1816,7 @@ static void zlc_clear_zones_full(struct zonelist *zonelist) > > > > static bool zone_local(struct zone *local_zone, struct zone *zone) > > { > > - return node_distance(local_zone->node, zone->node) == LOCAL_DISTANCE; > > + return zone_to_nid(zone) == numa_node_id(); > > Why numa_node_id()? We pass in the preferred zone as @local_zone: > Initially because I was thinking "local node" and numa_node_id() is a per-cpu variable that should be cheap to access and in some cases cache-hot as the top-level gfp API calls numa_node_id(). Thinking about it more though it still makes sense because the preferred zone is not necessarily local. If the allocation request requires ZONE_DMA32 and the local node does not have that zone then preferred zone is on a remote node. -- Mel Gorman SUSE Labs