[PATCH] mm/mm_init: fix incorrect node_spanned_pages

[Wei Yang <richard.weiyang@gmail.com>]

Current node_spanned_pages is got as a summation of all zone's spanned page
in calculate_node_totalpages(). Generally this is good, but if we use
kernelcore=mirror, it is would be wrong.

Without kernelcore=mirror:

    The test machine has below memory layout:

      memory[0x0]     [0x0000000000001000-0x000000000009efff], 0x000000000009e000 bytes on node 0 flags: 0x0
      memory[0x1]     [0x0000000000100000-0x00000000bffdefff], 0x00000000bfedf000 bytes on node 0 flags: 0x0
      memory[0x2]     [0x0000000100000000-0x00000001bfffffff], 0x00000000c0000000 bytes on node 0 flags: 0x0

    And the Zone range is:

      DMA      [mem 0x0000000000001000-0x0000000000ffffff]
      DMA32    [mem 0x0000000001000000-0x00000000ffffffff]
      Normal   [mem 0x0000000100000000-0x00000001bfffffff]

    Then we see, with spanned_pages printed:

      On node 0 spanned_pages: 1835007 totalpages: 1572733

With kernelcore=mirror:

    The test machine has below memory layout:

      memory[0x0]     [0x0000000000001000-0x000000000009efff], 0x000000000009e000 bytes on node 0 flags: 0x2
      memory[0x1]     [0x0000000000100000-0x00000000bffdefff], 0x00000000bfedf000 bytes on node 0 flags: 0x2
      memory[0x2]     [0x0000000100000000-0x000000013fffffff], 0x0000000040000000 bytes on node 0 flags: 0x2
      memory[0x3]     [0x0000000140000000-0x00000001bfffffff], 0x0000000080000000 bytes on node 0 flags: 0x0

    And the Zone range is:

      DMA      [mem 0x0000000000001000-0x0000000000ffffff]
      DMA32    [mem 0x0000000001000000-0x00000000ffffffff]
      Normal   [mem 0x0000000100000000-0x00000001bfffffff]
      Device   empty
    Movable zone start for each node
      Node 0: 0x0000000140000000

    Then we see, with spanned_pages printed:

      On node 0 spanned_pages: 2359295 totalpages: 1572733

The total range of memory on node 0 doesn't change, but the spanned_pages
becomes much larger.

The reason is when kernelcore=mirror is specified, the range of Zone Normal
and Zone Movable would overlap. So the overlapped range would be calculated
twice.

A wrong node_spanned_pages would effect defer_init(), since each
zone_end_pfn is less than pgdat_end_pfn().

As we already passed in node_start_pfn and node_end_pfn, fix this by get it
from (node_start_pfn - node_end_pfn) directly.

Fixes: 342332e6a925 ("mm/page_alloc.c: introduce kernelcore=mirror option")
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Cc: Yuan Liu <yuan1.liu@intel.com>
---
 mm/mm_init.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/mm/mm_init.c b/mm/mm_init.c
index a0e6a91283fb..7ad01eeddda9 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -1304,7 +1304,7 @@ static void __init calculate_node_totalpages(struct pglist_data *pgdat,
 						unsigned long node_start_pfn,
 						unsigned long node_end_pfn)
 {
-	unsigned long realtotalpages = 0, totalpages = 0;
+	unsigned long realtotalpages = 0;
 	enum zone_type i;
 
 	for (i = 0; i < MAX_NR_ZONES; i++) {
@@ -1334,11 +1334,10 @@ static void __init calculate_node_totalpages(struct pglist_data *pgdat,
 		zone->present_early_pages = real_size;
 #endif
 
-		totalpages += spanned;
 		realtotalpages += real_size;
 	}
 
-	pgdat->node_spanned_pages = totalpages;
+	pgdat->node_spanned_pages = node_end_pfn - node_start_pfn;
 	pgdat->node_present_pages = realtotalpages;
 	pr_debug("On node %d totalpages: %lu\n", pgdat->node_id, realtotalpages);
 }
-- 
2.34.1