Messages in this thread | | | Date | Sat, 1 Feb 2014 13:13:12 +0100 | From | Petr Tesarik <> | Subject | Re: [PATCH] x86: fix the initialization of physnode_map |
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On Fri, 31 Jan 2014 13:14:29 -0800 Dave Hansen <dave@sr71.net> wrote:
> 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?
Yes, that's it.
> 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? :)
In fact, this is a patch that has been floating around in SUSE Enterprise kernels for some time. It was originally added to pass certification on IBM SurePOS 700 x4900-785.
When cleaning up our kernel patches, I noticed that the bug is still present in the upstream kernel, so I posted this patch. While I don't have any evidence that someone actually needs the fix today, it seems wrong to leave buggy code in the kernel.
If you all agree that we rip off DISCONTIGMEM instead, I can post patches to do that and be equally happy. ;-)
> > 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?
If end belongs to a different section than start, the final section will not be initialized, yes.
> 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?
Exactly.
> 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.
Works for me.
Petr Tesarik
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