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Subject[PATCH] Allow nodes to exist that only contain ZONE_MOVABLE
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With the introduction of kernelcore=, a configurable zone is created on
request. In some cases, this value will be small enough that some nodes
contain only ZONE_MOVABLE. On some NUMA configurations when this occurs,
arch-independent zone-sizing will get the size of the memory holes within the
node incorrect. The value of present_pages goes negative and the boot fails.

This patch fixes the bug in the calculation of the size of the hole. The
test case is to boot test a NUMA machine with a low value of kernelcore=
before and after the patch is applied. While this bug exists in early kernel
it cannot be triggered in practice.

This patch has been boot-tested on a variety machines with and without
kernelcore= set.

Signed-off-by: Mel Gorman <mel@csn.ul.ie>

---
page_alloc.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 40954fb..6d3550c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2775,11 +2775,11 @@ unsigned long __meminit __absent_pages_in_range(int nid,
if (i == -1)
return 0;

+ prev_end_pfn = min(early_node_map[i].start_pfn, range_end_pfn);
+
/* Account for ranges before physical memory on this node */
if (early_node_map[i].start_pfn > range_start_pfn)
- hole_pages = early_node_map[i].start_pfn - range_start_pfn;
-
- prev_end_pfn = early_node_map[i].start_pfn;
+ hole_pages = prev_end_pfn - range_start_pfn;

/* Find all holes for the zone within the node */
for (; i != -1; i = next_active_region_index_in_nid(i, nid)) {
--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
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