From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id 91B026B005A for ; Mon, 21 Sep 2009 13:29:39 -0400 (EDT) Sender: owner-linux-mm@kvack.org Subject: Re: [PATCH 1/3] powerpc: Allocate per-cpu areas for node IDs for SLQB to use as per-node areas From: Daniel Walker In-Reply-To: <20090921102418.4692d62c.rdunlap@xenotime.net> References: <1253549426-917-1-git-send-email-mel@csn.ul.ie> <1253549426-917-2-git-send-email-mel@csn.ul.ie> <1253553472.9654.236.camel@desktop> <20090921102418.4692d62c.rdunlap@xenotime.net> Content-Type: text/plain Date: Mon, 21 Sep 2009 10:29:41 -0700 Message-Id: <1253554181.9654.238.camel@desktop> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit To: Randy Dunlap Cc: Mel Gorman , Nick Piggin , Pekka Enberg , Christoph Lameter , heiko.carstens@de.ibm.com, sachinp@in.ibm.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Tejun Heo , Benjamin Herrenschmidt List-ID: On Mon, 2009-09-21 at 10:24 -0700, Randy Dunlap wrote: > On Mon, 21 Sep 2009 10:17:52 -0700 Daniel Walker wrote: > > > On Mon, 2009-09-21 at 17:10 +0100, Mel Gorman wrote: > > > SLQB uses DEFINE_PER_CPU to define per-node areas. An implicit > > > assumption is made that all valid node IDs will have matching valid CPU > > > ids. In memoryless configurations, it is possible to have a node ID with > > > no CPU having the same ID. When this happens, a per-cpu are is not > > > created and the value of paca[cpu].data_offset is some random value. > > > This is later deferenced and the system crashes after accessing some > > > invalid address. > > > > > > This patch hacks powerpc to allocate per-cpu areas for node IDs that > > > have no corresponding CPU id. This gets around the immediate problem but > > > it should be discussed if there is a requirement for a DEFINE_PER_NODE > > > and how it should be implemented. > > > > > > Signed-off-by: Mel Gorman > > > --- > > > arch/powerpc/kernel/setup_64.c | 20 ++++++++++++++++++++ > > > 1 files changed, 20 insertions(+), 0 deletions(-) > > > > > > diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c > > > index 1f68160..a5f52d4 100644 > > > --- a/arch/powerpc/kernel/setup_64.c > > > +++ b/arch/powerpc/kernel/setup_64.c > > > @@ -588,6 +588,26 @@ void __init setup_per_cpu_areas(void) > > > paca[i].data_offset = ptr - __per_cpu_start; > > > memcpy(ptr, __per_cpu_start, __per_cpu_end - __per_cpu_start); > > > } > > > +#ifdef CONFIG_SLQB > > > + /* > > > + * SLQB abuses DEFINE_PER_CPU to setup a per-node area. This trick > > > + * assumes that ever node ID will have a CPU of that ID to match. > > > + * On systems with memoryless nodes, this may not hold true. Hence, > > > + * we take a second pass initialising a "per-cpu" area for node-ids > > > + * that SLQB can use > > > + */ > > > > Very trivial, but there's a little trailing whitespace in the first line > > of the comment (checkpatch warns on it.) You also spelled initializing > > wrong. > > re: spelling. Not really. Think internationally. Yeah, I realized that after I sent it .. So misspelled in the American sense I guess. Daniel -- 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