linux-kernel - Re: [PATCH] Fake NUMA emulation for PowerPC (Take 2)

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Message-ID: <20080126071339.GA25328@balbir.in.ibm.com>
Date:	Sat, 26 Jan 2008 12:43:39 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Michael Ellerman <michael@...erman.id.au>
Cc:	linuxppc-dev@...abs.org, LKML <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH] Fake NUMA emulation for PowerPC (Take 2)

* Michael Ellerman <michael@...erman.id.au> [2008-01-18 16:44:58]:

> 
> This fixes it, although I'm a little worried about some of the
> removals/movings of node_set_online() in the patch.
> 
> 
> diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
> index 1666e7d..dcedc26 100644
> --- a/arch/powerpc/mm/numa.c
> +++ b/arch/powerpc/mm/numa.c
> @@ -49,7 +49,6 @@ static int __cpuinit fake_numa_create_new_node(unsigned long end_pfn,
>  	static unsigned int fake_nid = 0;
>  	static unsigned long long curr_boundary = 0;
>  
> -	*nid = fake_nid;
>  	if (!p)
>  		return 0;
>  
> @@ -60,6 +59,7 @@ static int __cpuinit fake_numa_create_new_node(unsigned long end_pfn,
>  	if (mem < curr_boundary)
>  		return 0;
>  
> +	*nid = fake_nid;
>  	curr_boundary = mem;
>  
>  	if ((end_pfn << PAGE_SHIFT) > mem) {
> 

Hi, Michael,

Here's a better and more complete fix for the problem. Could you
please see if it works for you? I tested it on a real NUMA box and it
seemed to work fine there.

Description
-----------

This patch provides a fix for the problem found by
Michael Ellerman <michael@...erman.id.au> while using fake NUMA nodes
on a cell box. The code modifies node id iff (as in if and only if)
fake NUMA nodes are created.

Signed-off-by: Balbir Singh <balbir@...ux.vnet.ibm.com>
---

 arch/powerpc/mm/numa.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff -puN arch/powerpc/mm/numa.c~fix-fake-numa-nid-on-numa arch/powerpc/mm/numa.c
--- linux-2.6.24-rc8/arch/powerpc/mm/numa.c~fix-fake-numa-nid-on-numa	2008-01-26 12:20:29.000000000 +0530
+++ linux-2.6.24-rc8-balbir/arch/powerpc/mm/numa.c	2008-01-26 12:27:53.000000000 +0530
@@ -49,7 +49,12 @@ static int __cpuinit fake_numa_create_ne
 	static unsigned int fake_nid = 0;
 	static unsigned long long curr_boundary = 0;
 
-	*nid = fake_nid;
+	/*
+	 * If we did enable fake nodes and cross a node,
+	 * remember the last node and start from there.
+	 */
+	if (fake_nid)
+		*nid = fake_nid;
 	if (!p)
 		return 0;
 
_

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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