linux-kernel - Re: [PATCH 1/5] x86: Change size of node ids from u8 to u16 fixup

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Date:	Sat, 19 Jan 2008 13:25:32 -0800
From:	Mike Travis <travis@....com>
To:	David Rientjes <rientjes@...gle.com>
CC:	Yinghai Lu <yhlu.kernel@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@...e.de>, mingo@...e.hu,
	Christoph Lameter <clameter@....com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Eric Dumazet <dada1@...mosbay.com>
Subject: Re: [PATCH 1/5] x86: Change size of node ids from u8 to u16 fixup

David Rientjes wrote:
> On Fri, 18 Jan 2008, Yinghai Lu wrote:
> 
>>> +#if MAX_NUMNODES > 256
>>> +typedef u16 numanode_t;
>>> +#else
>>> +typedef u8 numanode_t;
>>> +#endif
>>> +
>>>  #endif /* _LINUX_NUMA_H */
>> that is wrong, you can not change pxm_to_node_map from int to u8 or u16.
>>

Thanks for finding this!

> 
> Yeah, NID_INVAL is negative so no unsigned type will work here, 
> unfortunately.  And that reduces the intended savings of your change since 
> the smaller type can only be used with a smaller CONFIG_NODES_SHIFT.
> 

Excuse my ignorance but why wouldn't this work:

static numanode_t pxm_to_node_map[MAX_PXM_DOMAINS]
                                = { [0 ... MAX_PXM_DOMAINS - 1] = NUMA_NO_NODE };
...
>> int acpi_map_pxm_to_node(int pxm)
>> {
>         int node = pxm_to_node_map[pxm];
> 
>         if (node < 0)

	   numanode_t node = pxm_to_node_map[pxm];

	   if (node != NUMA_NO_NODE) {
>>                 if (nodes_weight(nodes_found_map) >= MAX_NUMNODES)
>>                         return NID_INVAL;
>>                 node = first_unset_node(nodes_found_map);
>>                 __acpi_map_pxm_to_node(pxm, node);
>>                 node_set(node, nodes_found_map);
>>         }

or change:
	#define NID_INVAL       (-1)
to
	#define NID_INVAL       ((numanode_t)(-1))
...
	   if (node != NID_INVAL) {
>>                 if (nodes_weight(nodes_found_map) >= MAX_NUMNODES)
>>                         return NID_INVAL;
>>                 node = first_unset_node(nodes_found_map);
>>                 __acpi_map_pxm_to_node(pxm, node);
>>                 node_set(node, nodes_found_map);
>>         }

Though why there two "node invalid" values I'm not sure... ?

>>
>>         return node;
>> }

And btw, shouldn't the pxm value be sized to numanode_t size as well?
Will it ever be larger than the largest node id?

Thanks,
Mike
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