linux-kernel - Re: [PATCH] x86/mm/srat_64.c: nodes_parsed should include all nodes detected by ACPI.

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Message-ID: <alpine.DEB.2.00.1001171338170.16238@chino.kir.corp.google.com>
Date:	Sun, 17 Jan 2010 13:53:18 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Haicheng Li <haicheng.li@...ux.intel.com>
cc:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/mm/srat_64.c: nodes_parsed should include all nodes
 detected by ACPI.

On Fri, 15 Jan 2010, Haicheng Li wrote:

> This is to fix the bug discussed in email thread:
> http://patchwork.kernel.org/patch/69499/.
> 

It would be better to include a brief synopsis of the problem in the 
changelog instead of a citation, otherwise it obfuscates the issue it 
solves.

> Currently node_possible_map won't include the offlined node that has neither
> CPU onlined nor MEM onlined at booting time. As a result, nr_node_ids won't be
> equal to possible nodes.
> 
> CC: Thomas Gleixner <tglx@...utronix.de>
> CC: Ingo Molnar <mingo@...hat.com>
> CC: H. Peter Anvin <hpa@...or.com>
> CC: Andi Kleen <andi@...stfloor.org>
> Signed-off-by: Haicheng Li <haicheng.li@...ux.intel.com>
> ---
>  arch/x86/mm/srat_64.c |   10 ++--------
>  1 files changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/mm/srat_64.c b/arch/x86/mm/srat_64.c
> index a271241..a5bc297 100644
> --- a/arch/x86/mm/srat_64.c
> +++ b/arch/x86/mm/srat_64.c
> @@ -238,7 +238,7 @@ update_nodes_add(int node, unsigned long start, unsigned
> long end)
>  void __init
>  acpi_numa_memory_affinity_init(struct acpi_srat_mem_affinity *ma)
>  {
> -	struct bootnode *nd, oldnode;
> +	struct bootnode *nd;
>  	unsigned long start, end;
>  	int node, pxm;
>  	int i;
> @@ -277,7 +277,6 @@ acpi_numa_memory_affinity_init(struct
> acpi_srat_mem_affinity *ma)
>  		return;
>  	}
>  	nd = &nodes[node];
> -	oldnode = *nd;
>  	if (!node_test_and_set(node, nodes_parsed)) {
>  		nd->start = start;
>  		nd->end = end;
> @@ -291,13 +290,8 @@ acpi_numa_memory_affinity_init(struct
> acpi_srat_mem_affinity *ma)
>  	printk(KERN_INFO "SRAT: Node %u PXM %u %lx-%lx\n", node, pxm,
>  	       start, end);
> 
> -	if (ma->flags & ACPI_SRAT_MEM_HOT_PLUGGABLE) {
> +	if (ma->flags & ACPI_SRAT_MEM_HOT_PLUGGABLE)
>  		update_nodes_add(node, start, end);
> -		/* restore nodes[node] */
> -		*nd = oldnode;
> -		if ((nd->start | nd->end) == 0)
> -			node_clear(node, nodes_parsed);
> -	}
> 
>  	node_memblk_range[num_node_memblks].start = start;
>  	node_memblk_range[num_node_memblks].end = end;

There're a couple of issues with this patch:

 - it breaks CONFIG_MEMORY_HOTPLUG_SPARSE kernels when the SRAT reports 
   more than one entry for a single node id and the later entry does not
   specify an address range, and

 - carrying the bit for the node over in nodes_parsed is inappropriate
   since other x86 code depends on that map including only nodes with
   memory such as e820_register_active_regions() and nodes_cover_memory().

    [ The existing naming is admittedly convoluted since nodes_parsed
      represents nodes with memory and cpu_nodes_parsed represents nodes
      with only cpus; in actuality, they should probably be
      mem_nodes_parsed and no_mem_nodes_parsed, respectively, since the
      latter will now include hotpluggable nodes. ]

To fix both of these issues simultaneously, I think it would be better to 
set the bit in no_mem_nodes_parsed so that it gets unioned in 
acpi_scan_nodes() when nodes_possible_map is actually formed.
--
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