[RFC Patch 1/3] mm/mm_init: adjust overlapped zone for mirror memory too

[Wei Yang]

When mirrored_kernelcore is set, adjust_zone_range_for_zone_movable() would
skip the adjustment if ZONE_MOVABLE starts within one zone.

This makes the zone, usually ZONE_NORMAL, ends the same as ZONE_MOVABLE.

For example, we have a system with following 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

With kernelcore=mirror set, current kernel set zone with below range:

  Normal  [100000, 1c0000]
  Movable [140000, 1c0000]

This changes the expected behavior of defer_init(), because it only expect to
defer_init() memory in last zone. As Zone Normal and Movable stops at the same
end_pfn, defer_init() would set first_deferred_pfn in Zone Normal. And what is
worse, pages belongs to Zone Normal would be counted as Zone Movable.

  Node 0, zone   Normal
          spanned  786432
          present  262144
          managed  34390
  Node 0, zone  Movable
          spanned  524288
          present  524288
          managed  715855    <- manage more pages than present

While when we look at the memory layout, we can see Zone Normal and Movable
could be not overlapped if we adjust Zone Normal just other movable zone case.
And we don't expect they would interleave.

After doing so, we have non-overlap Zones:

  Normal  [100000, 140000]
  Movable [140000, 1c0000]

And the page locality looks correct:

  Node 0, zone   Normal
          spanned  262144
          present  262144
          managed  233614
  Node 0, zone  Movable
          spanned  524288
          present  524288
          managed  524242

Fixes: 342332e6a925 ("mm/page_alloc.c: introduce kernelcore=mirror option")
Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx>
Cc: "David Hildenbrand (Arm)" <david@xxxxxxxxxx>
Cc: Yuan Liu <yuan1.liu@xxxxxxxxx>
---
 mm/mm_init.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/mm_init.c b/mm/mm_init.c
index 7c4af27a6557..b8ff4aff19c0 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -1170,8 +1170,7 @@ static void __init adjust_zone_range_for_zone_movable(int nid,
 				arch_zone_highest_possible_pfn[movable_zone]);
 
 		/* Adjust for ZONE_MOVABLE starting within this range */
-		} else if (!mirrored_kernelcore &&
-			*zone_start_pfn < zone_movable_pfn[nid] &&
+		} else if (*zone_start_pfn < zone_movable_pfn[nid] &&
 			*zone_end_pfn > zone_movable_pfn[nid]) {
 			*zone_end_pfn = zone_movable_pfn[nid];
 
-- 
2.34.1