From: Andy Whitcroft The part of the sparsemem patch which modifies memmap_init_zone() has recently become a problem. It changes behavior so that there is a call to pfn_to_page() for each individual page inside of a node's range: node_start_pfn through node_end_pfn. It used to simply do this once, at the beginning of the node, but having sparsemem's non-contiguous mem_map[]s inside of a node made it necessary to change. Mike Kravetz recently wrote a patch which made the NUMA code accept some new kinds of layouts. The system's memory was laid out like this, with node 0's memory in two pieces: one before and one after node 1's memory: Node 0: +++++ +++++ Node 1: +++++ Previous behavior before Mike's patch was to assign nodes like this: Node 0: 00000 XXXXX Node 1: 11111 Where the 'X' areas were simply thrown away. The new behavior was to make the pg_data_t span node 0 across all of its areas, including areas that are really node 1's: Node 0: 000000000000000 Node 1: 11111 This wastes a little bit of mem_map space, but ends up being OK, and more fully utilizes the system's memory. memmap_init_zone() initializes all of the "struct page"s for node 0, even for the "hole", but those never get used, because there is no pfn_to_page() that resolves to those pages. However, only calling pfn_to_page() once, memmap_init_zone() always uses the pages that were allocated for node0->node_mem_map because: struct page *start = pfn_to_page(start_pfn); // effectively start = &node->node_mem_map[0] for (page = start; page < (start + size); page++) { init_page_here();... page++; } Slow, and wasteful, but generally harmless. But, modify that to call pfn_to_page() for each loop iteration (like sparsemem does): for (pfn = start_pfn; pfn < < (start_pfn + size); pfn++++) { page = pfn_to_page(pfn); } And you end up trying to initialize node 1's pages too early, along with bogus data from node 0. This patch checks for those weird layouts and declines to touch the pages, making the more frequent pfn_to_page() calls OK to do. Signed-off-by: Dave Hansen Signed-off-by: Andy Whitcroft Signed-off-by: Andrew Morton --- arch/ppc64/Kconfig | 12 ++++++++++++ include/linux/mmzone.h | 6 ++++++ mm/page_alloc.c | 2 ++ 3 files changed, 20 insertions(+) diff -puN arch/ppc64/Kconfig~sparsemem-swiss-cheese-numa-layouts arch/ppc64/Kconfig --- 25/arch/ppc64/Kconfig~sparsemem-swiss-cheese-numa-layouts Fri May 6 14:58:52 2005 +++ 25-akpm/arch/ppc64/Kconfig Fri May 6 14:58:52 2005 @@ -211,6 +211,18 @@ config ARCH_FLATMEM_ENABLE source "mm/Kconfig" +# Some NUMA nodes have memory ranges that span +# other nodes. Even though a pfn is valid and +# between a node's start and end pfns, it may not +# reside on that node. +# +# This is a relatively temporary hack that should +# be able to go away when sparsemem is fully in +# place +config NODES_SPAN_OTHER_NODES + def_bool y + depends on NEED_MULTIPLE_NODES + config NUMA bool "NUMA support" depends on DISCONTIGMEM diff -puN include/linux/mmzone.h~sparsemem-swiss-cheese-numa-layouts include/linux/mmzone.h --- 25/include/linux/mmzone.h~sparsemem-swiss-cheese-numa-layouts Fri May 6 14:58:52 2005 +++ 25-akpm/include/linux/mmzone.h Fri May 6 14:58:52 2005 @@ -511,6 +511,12 @@ void sparse_init(void); #define sparse_init() do {} while (0) #endif /* CONFIG_SPARSEMEM */ +#ifdef CONFIG_NODES_SPAN_OTHER_NODES +#define early_pfn_in_nid(pfn, nid) (early_pfn_to_nid(pfn) == (nid)) +#else +#define early_pfn_in_nid(pfn, nid) (1) +#endif + #ifndef early_pfn_valid #define early_pfn_valid(pfn) (1) #endif diff -puN mm/page_alloc.c~sparsemem-swiss-cheese-numa-layouts mm/page_alloc.c --- 25/mm/page_alloc.c~sparsemem-swiss-cheese-numa-layouts Fri May 6 14:58:52 2005 +++ 25-akpm/mm/page_alloc.c Fri May 6 14:58:52 2005 @@ -1594,6 +1594,8 @@ void __init memmap_init_zone(unsigned lo for (pfn = start_pfn; pfn < end_pfn; pfn++, page++) { if (!early_pfn_valid(pfn)) continue; + if (!early_pfn_in_nid(pfn, nid)) + continue; page = pfn_to_page(pfn); set_page_links(page, zone, nid, pfn); set_page_count(page, 0); _