[patch] mm: Ensure proper alignment for node_remap_start_pfn

[patch] mm: Ensure proper alignment for node_remap_start_pfn

[Ravikiran G Thirumalai]

While reserving KVA for lmem_maps of node, we have to make sure that
node_remap_start_pfn[] is aligned to a proper pmd boundary.
(node_remap_start_pfn[] gets its value from node_end_pfn[])

Signed-off-by: Ravikiran Thirumalai <kiran@scalex86.org>
Signed-off-by: Shai Fultheim <shai@scalex86.org>

Index: linux-2.6.13-rc3/arch/i386/mm/discontig.c
===================================================================
--- linux-2.6.13-rc3.orig/arch/i386/mm/discontig.c	2005-07-26 15:10:25.000000000 -0700
+++ linux-2.6.13-rc3/arch/i386/mm/discontig.c	2005-07-26 16:27:43.000000000 -0700
@@ -243,6 +243,14 @@
 		/* now the roundup is correct, convert to PAGE_SIZE pages */
 		size = size * PTRS_PER_PTE;
 
+		if (node_end_pfn[nid] & (PTRS_PER_PTE-1)) {
+			/* 
+			 * Adjust size if node_end_pfn is not on a proper 
+			 * pmd boundary. remap_numa_kva will barf otherwise.
+			 */
+			size +=  node_end_pfn[nid] & (PTRS_PER_PTE-1);
+		}
+
 		/*
 		 * Validate the region we are allocating only contains valid
 		 * pages.
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Re: [patch] mm: Ensure proper alignment for node_remap_start_pfn

[Andrew Morton]

Ravikiran G Thirumalai <kiran@scalex86.org> wrote:
>
> While reserving KVA for lmem_maps of node, we have to make sure that
> node_remap_start_pfn[] is aligned to a proper pmd boundary.
> (node_remap_start_pfn[] gets its value from node_end_pfn[])
> 

What are the effects of not having this patch applied?  Does someone's
computer crash, or what?

IOW: what problem is this fixing, precisely?

> 
> Index: linux-2.6.13-rc3/arch/i386/mm/discontig.c
> ===================================================================
> --- linux-2.6.13-rc3.orig/arch/i386/mm/discontig.c	2005-07-26 15:10:25.000000000 -0700
> +++ linux-2.6.13-rc3/arch/i386/mm/discontig.c	2005-07-26 16:27:43.000000000 -0700
> @@ -243,6 +243,14 @@
>  		/* now the roundup is correct, convert to PAGE_SIZE pages */
>  		size = size * PTRS_PER_PTE;
>  
> +		if (node_end_pfn[nid] & (PTRS_PER_PTE-1)) {
> +			/* 
> +			 * Adjust size if node_end_pfn is not on a proper 
> +			 * pmd boundary. remap_numa_kva will barf otherwise.
> +			 */
> +			size +=  node_end_pfn[nid] & (PTRS_PER_PTE-1);
> +		}
> +
>  		/*
>  		 * Validate the region we are allocating only contains valid
>  		 * pages.
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Re: [patch] mm: Ensure proper alignment for node_remap_start_pfn

[Ravikiran G Thirumalai]

On Wed, Jul 27, 2005 at 06:17:24PM -0700, Andrew Morton wrote:
> Ravikiran G Thirumalai <kiran@scalex86.org> wrote:
> >
> > While reserving KVA for lmem_maps of node, we have to make sure that
> > node_remap_start_pfn[] is aligned to a proper pmd boundary.
> > (node_remap_start_pfn[] gets its value from node_end_pfn[])
> > 
> 
> What are the effects of not having this patch applied?  Does someone's
> computer crash, or what?

Yes, it does cause a crash.

Thanks,
Kiran
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Re: [patch] mm: Ensure proper alignment for node_remap_start_pfn

[Dave Hansen]

On Wed, 2005-07-27 at 18:31 -0700, Ravikiran G Thirumalai wrote:
> On Wed, Jul 27, 2005 at 06:17:24PM -0700, Andrew Morton wrote:
> > Ravikiran G Thirumalai <kiran@scalex86.org> wrote:
> > >
> > > While reserving KVA for lmem_maps of node, we have to make sure that
> > > node_remap_start_pfn[] is aligned to a proper pmd boundary.
> > > (node_remap_start_pfn[] gets its value from node_end_pfn[])
> > > 
> > 
> > What are the effects of not having this patch applied?  Does someone's
> > computer crash, or what?
> 
> Yes, it does cause a crash.

I don't know of any NUMA x86 sub-arches that have nodes which are
aligned on any less than 2MB.  Is this an architecture that's supported
in the tree, today?

-- Dave

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Re: [patch] mm: Ensure proper alignment for node_remap_start_pfn

[Ravikiran G Thirumalai]

On Thu, Jul 28, 2005 at 10:20:26AM -0700, Dave Hansen wrote:
> On Wed, 2005-07-27 at 18:31 -0700, Ravikiran G Thirumalai wrote:
> > On Wed, Jul 27, 2005 at 06:17:24PM -0700, Andrew Morton wrote:
> > > Ravikiran G Thirumalai <kiran@scalex86.org> wrote:
> > > >
> > Yes, it does cause a crash.
> 
> I don't know of any NUMA x86 sub-arches that have nodes which are
> aligned on any less than 2MB.  Is this an architecture that's supported
> in the tree, today?

SRAT need not guarantee any alignment at all in the memory affinity 
structure (the address in 64-bit byte address).   And yes, there are x86-numa
machines that run the latest kernel tree and face this problem.

Thanks,
Kiran
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Re: [patch] mm: Ensure proper alignment for node_remap_start_pfn

[Dave Hansen]

On Thu, 2005-07-28 at 11:14 -0700, Ravikiran G Thirumalai wrote:
> SRAT need not guarantee any alignment at all in the memory affinity 
> structure (the address in 64-bit byte address)

The Summit machines (the only x86 user of the SRAT) have other hardware
guarantees about alignment, so I guess that's why we've never
encountered it.  Are you using the SRAT on non-Summit hardware?  That
doesn't seem possible:

arch/i386/Kconfig:
        config ACPI_SRAT
                bool
                default y
                depends on NUMA && (X86_SUMMIT || X86_GENERICARCH)
        
> And yes, there are x86-numa
> machines that run the latest kernel tree and face this problem.

I didn't say "run the latest kernel tree".  *In* the latest kernel
tree :)

-- Dave

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