linux-kernel - Re: [PATCH] x86: fix the initialization of physnode

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Date:	Fri, 31 Jan 2014 13:14:29 -0800
From:	Dave Hansen <dave@...1.net>
To:	Petr Tesarik <ptesarik@...e.cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
CC:	Jiang Liu <liuj97@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: fix the initialization of physnode_map

On 01/31/2014 02:05 AM, Petr Tesarik wrote:
> With DISCONTIGMEM, the mapping between a pfn and its owning node is
> initialized using data provided by the BIOS or from the command line.
> However, the initialization may fail if the extents are not aligned
> to section boundary (64M).

So is this a problem that shows up with DISCONTIGMEM?  Just curious, but
what the heck kind of 32-bit NUMA hardware is still in the wild?  Did
someon buy a NUMA-Q on eBay? :)

>  void memory_present(int nid, unsigned long start, unsigned long end)
>  {
> -	unsigned long pfn;
> +	unsigned long sect, endsect;
>  
>  	printk(KERN_INFO "Node: %d, start_pfn: %lx, end_pfn: %lx\n",
>  			nid, start, end);
>  	printk(KERN_DEBUG "  Setting physnode_map array to node %d for pfns:\n", nid);
>  	printk(KERN_DEBUG "  ");
> -	for (pfn = start; pfn < end; pfn += PAGES_PER_SECTION) {
> -		physnode_map[pfn / PAGES_PER_SECTION] = nid;
> -		printk(KERN_CONT "%lx ", pfn);
> +	endsect = (end - 1) / PAGES_PER_SECTION;
> +	for (sect = start / PAGES_PER_SECTION; sect <= endsect; ++sect) {
> +		physnode_map[sect] = nid;
> +		printk(KERN_CONT "%lx ", sect * PAGES_PER_SECTION);
>  	}
>  	printk(KERN_CONT "\n");
>  }

So, if start and end are not aligned to section boundaries, we will miss
setting physnode_map[] for the final section?

For instance, if we have a 64MB section size and try to call
memory_present(32MB -> 96MB), we will set 0->64MB present, but not set
the 64MB->128MB section as present.

Right?

Can you just align 'start' down to the section's start and 'end' up to
the end of the section that contains it?  I guess you do that
implicitly, but you should be able to do it without refactoring the for
loop entirely.

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