[PATCH] mm/mm_init: fix incorrect node_spanned_pages

[PATCH] mm/mm_init: fix incorrect node_spanned_pages

[Wei Yang]

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

Re: [PATCH] mm/mm_init: fix incorrect node_spanned_pages

[Mike Rapoport]

Hi Wei,

On Mon, Jun 22, 2026 at 02:24:03AM +0000, Wei Yang wrote:
> 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.
>
> 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>

I queued it for now, will push to one of memblock branches after merge
window closes.

> ---
>  mm/mm_init.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)

-- 
Sincerely yours,
Mike.

Re: [PATCH] mm/mm_init: fix incorrect node_spanned_pages

[Wei Yang]

On Mon, Jun 22, 2026 at 04:58:47PM +0300, Mike Rapoport wrote:
>Hi Wei,

Hi, Mike

>
>On Mon, Jun 22, 2026 at 02:24:03AM +0000, Wei Yang wrote:
>> 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.
>>
>> 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>
>
>I queued it for now, will push to one of memblock branches after merge
>window closes.
>

After some investigation, I found current mirrored_kernelcore may still affect
memmap_init() in some aspects.

But how to fix is not sure, will prepare an RFC for discussion.

>> ---
>>  mm/mm_init.c | 5 ++---
>>  1 file changed, 2 insertions(+), 3 deletions(-)
>
>-- 
>Sincerely yours,
>Mike.

-- 
Wei Yang
Help you, Help me

Re: [PATCH] mm/mm_init: fix incorrect node_spanned_pages

[Mike Rapoport]

Hi Wei,

On Tue, Jun 23, 2026 at 08:35:07AM +0000, Wei Yang wrote:
> On Mon, Jun 22, 2026 at 04:58:47PM +0300, Mike Rapoport wrote:
> >On Mon, Jun 22, 2026 at 02:24:03AM +0000, Wei Yang wrote:
> >> 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.
> >>
> >> 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>
> >
> >I queued it for now, will push to one of memblock branches after merge
> >window closes.
> >
> 
> After some investigation, I found current mirrored_kernelcore may still affect
> memmap_init() in some aspects.
> 
> But how to fix is not sure, will prepare an RFC for discussion.

After I applied your patch, I did some checks to see why
mirrored_kernelcore causes us troubles. I found that unlike other variants
of kernelcore/movablecore settings, mirrored_kernelcore creates zone
overlap for no apparent reason. I did some git archaeology and I didn't
find a justification for making overlapping pages absent in ZONE_NORMAL.

So I came up with this cleanup:

https://git.kernel.org/pub/scm/linux/kernel/git/rppt/linux.git/log/?h=kernelcore-mirror

I'm waiting for the bots to chew on it before positing the patches.
 
> -- 
> Wei Yang
> Help you, Help me

-- 
Sincerely yours,
Mike.

Re: [PATCH] mm/mm_init: fix incorrect node_spanned_pages

[Wei Yang]

On Tue, Jun 23, 2026 at 12:22:15PM +0300, Mike Rapoport wrote:
>Hi Wei,
>
>On Tue, Jun 23, 2026 at 08:35:07AM +0000, Wei Yang wrote:
>> On Mon, Jun 22, 2026 at 04:58:47PM +0300, Mike Rapoport wrote:
>> >On Mon, Jun 22, 2026 at 02:24:03AM +0000, Wei Yang wrote:
>> >> 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.
>> >>
>> >> 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>
>> >
>> >I queued it for now, will push to one of memblock branches after merge
>> >window closes.
>> >
>> 
>> After some investigation, I found current mirrored_kernelcore may still affect
>> memmap_init() in some aspects.
>> 
>> But how to fix is not sure, will prepare an RFC for discussion.
>
>After I applied your patch, I did some checks to see why
>mirrored_kernelcore causes us troubles. I found that unlike other variants
>of kernelcore/movablecore settings, mirrored_kernelcore creates zone
>overlap for no apparent reason. I did some git archaeology and I didn't
>find a justification for making overlapping pages absent in ZONE_NORMAL.
>
>So I came up with this cleanup:
>
>https://git.kernel.org/pub/scm/linux/kernel/git/rppt/linux.git/log/?h=kernelcore-mirror
>
>I'm waiting for the bots to chew on it before positing the patches.
> 

Ah, just the same as I do :-).

>> -- 
>> Wei Yang
>> Help you, Help me
>
>-- 
>Sincerely yours,
>Mike.

-- 
Wei Yang
Help you, Help me