linux-kernel - Re: + powerpc-fix-code-for-reserved-memory-spanning-across-nodes.patch added to -mm tree

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Date:	Tue, 10 Feb 2009 17:05:45 +0530
From:	Chandru <chandru@...ibm.com>
To:	Johannes Weiner <hannes@...xchg.org>
CC:	linux-kernel@...r.kernel.org, mm-commits@...r.kernel.org,
	benh@...nel.crashing.org, chandru@...ux.vnet.ibm.com,
	paulus@...ba.org, akpm@...ux-foundation.org
Subject: Re: + powerpc-fix-code-for-reserved-memory-spanning-across-nodes.patch
 added to -mm tree

Johannes Weiner wrote:
> ---
> From: Johannes Weiner <hannes@...xchg.org>
> Subject: powerpc: fix rounding error in teaching bootmem about LMB
>
> If the reserved LMB does not exactly span complete pages, treating
> (start + size) >> PAGE_SHIFT as the ending PFN is an off by one error.
>
> The subsequent check for whether the region needs to be trimmed to fit
> the underlying node can now fail if the range exceeds the node by 1 to
> PAGE_SIZE - 1 bytes.  The excessive range is then passed to bootmem
> which BUG()s out on it correctly.
>
> Fix up the rounding to include all pages the LMB spans, even partial
> ones.
>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> ---

Hello Hannes,

Dave Hansen gave a fix for this problem which looks similar
to the changes that you have made here , but has an additional
one line change too. Here is the patch ( probably may not apply
cleanly to the latest kernel ) . I don' t know if Dave
submitted this patch to lkml for it's inclusion into the
latest tree. Thanks for looking into this issue. We may also have
to remove the 
powerpc-fix-code-for-reserved-memory-spanning-across-nodes.patch
from the -mm tree.

Thanks,
Chandru

=================
Snippet from Dave's patch without change log

---

 linux-2.6.git-dave/arch/powerpc/mm/numa.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff -puN arch/powerpc/mm/numa.c~reserve-over-fix arch/powerpc/mm/numa.c
--- linux-2.6.git/arch/powerpc/mm/numa.c~reserve-over-fix	2009-01-26 10:17:20.000000000 -0800
+++ linux-2.6.git-dave/arch/powerpc/mm/numa.c	2009-01-26 10:17:30.000000000 -0800
@@ -19,6 +19,7 @@
 #include <linux/notifier.h>
 #include <linux/lmb.h>
 #include <linux/of.h>
+#include <linux/pfn.h>
 #include <asm/sparsemem.h>
 #include <asm/prom.h>
 #include <asm/system.h>
@@ -882,7 +883,7 @@ static void mark_reserved_regions_for_ni
 		unsigned long physbase = lmb.reserved.region[i].base;
 		unsigned long size = lmb.reserved.region[i].size;
 		unsigned long start_pfn = physbase >> PAGE_SHIFT;
-		unsigned long end_pfn = ((physbase + size) >> PAGE_SHIFT);
+		unsigned long end_pfn = PFN_UP(physbase + size);
 		struct node_active_region node_ar;
 		unsigned long node_end_pfn = node->node_start_pfn +
 					     node->node_spanned_pages;
@@ -908,7 +909,7 @@ static void mark_reserved_regions_for_ni
 			 */
 			if (end_pfn > node_ar.end_pfn)
 				reserve_size = (node_ar.end_pfn << PAGE_SHIFT)
-					- (start_pfn << PAGE_SHIFT);
+					- physbase;
 			/*
 			 * Only worry about *this* node, others may not
 			 * yet have valid NODE_DATA().
diff -puN arch/powerpc/kernel/prom_init.c~reserve-over-fix arch/powerpc/kernel/prom_init.c


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