[PATCH 0/2] mm/mm_init: don't overlap zones with kernelcore=mirror

[PATCH 0/2] mm/mm_init: don't overlap zones with kernelcore=mirror

[Mike Rapoport]

From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>

Hi,

These patches make the behaviour of kernelcore= parameter uniform and
treat mirror just as another way to size the zones and cleanup a weird
part of the memory map initialization.
   
Mike Rapoport (Microsoft) (2):
  mm/mm_init: don't overlap NORMAL and MOVABLE zones with kernelcore=mirror
  mm/mm_init: drop overlap_memmap_init()

 mm/mm_init.c | 60 +++-------------------------------------------------
 1 file changed, 3 insertions(+), 57 deletions(-)


base-commit: 4549871118cf616eecdd2d939f78e3b9e1dddc48
-- 
2.53.0

[PATCH 1/2] mm/mm_init: don't overlap NORMAL and MOVABLE zones with kernelcore=mirror

[Mike Rapoport]

From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>

When kernelcore or movablecore kernel parameters define size of the
NORMAL and MOVABLE zones as percents of the total memory or by absolute
value, ZONE_NORMAL is clamped at the beginning of ZONE_MOVABLE.

However, when kernelcore=mirror the ZONE_NORMAL span is not changed but
rather pages from ZONE_MOVABLE counted as absent in ZONE_NORMAL.

Make the behaviour of kernelcore= parameter uniform and treat mirror
just as another way to size the zones.

Co-developed-by: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
 mm/mm_init.c | 36 +++---------------------------------
 1 file changed, 3 insertions(+), 33 deletions(-)

diff --git a/mm/mm_init.c b/mm/mm_init.c
index f9f8e1af921c..dce9dc9f2302 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -1159,9 +1159,8 @@ 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] &&
-			*zone_end_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];
 
 		/* Check if this whole range is within ZONE_MOVABLE */
@@ -1209,40 +1208,11 @@ static unsigned long __init zone_absent_pages_in_node(int nid,
 					unsigned long zone_start_pfn,
 					unsigned long zone_end_pfn)
 {
-	unsigned long nr_absent;
-
 	/* zone is empty, we don't have any absent pages */
 	if (zone_start_pfn == zone_end_pfn)
 		return 0;
 
-	nr_absent = __absent_pages_in_range(nid, zone_start_pfn, zone_end_pfn);
-
-	/*
-	 * ZONE_MOVABLE handling.
-	 * Treat pages to be ZONE_MOVABLE in ZONE_NORMAL as absent pages
-	 * and vice versa.
-	 */
-	if (mirrored_kernelcore && zone_movable_pfn[nid]) {
-		unsigned long start_pfn, end_pfn;
-		struct memblock_region *r;
-
-		for_each_mem_region(r) {
-			start_pfn = clamp(memblock_region_memory_base_pfn(r),
-					  zone_start_pfn, zone_end_pfn);
-			end_pfn = clamp(memblock_region_memory_end_pfn(r),
-					zone_start_pfn, zone_end_pfn);
-
-			if (zone_type == ZONE_MOVABLE &&
-			    memblock_is_mirror(r))
-				nr_absent += end_pfn - start_pfn;
-
-			if (zone_type == ZONE_NORMAL &&
-			    !memblock_is_mirror(r))
-				nr_absent += end_pfn - start_pfn;
-		}
-	}
-
-	return nr_absent;
+	return __absent_pages_in_range(nid, zone_start_pfn, zone_end_pfn);
 }
 
 /*
-- 
2.53.0

[PATCH 2/2] mm/mm_init: drop overlap_memmap_init()

[Mike Rapoport]

From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>

When ZONE_NORMAL and ZONE_MOVABLE could overlap because kernelcore=mirror
didn't reduce the span of ZONE_NORMAL, initialization of the memory map had
to skip overlapping pages during initialization of ZONE_MOVABLE to avoid
double initialization of the same struct pages.

Since kernelcore=mirror works now the same way as other variants of
kernelcore=/movablecore=, and adjusts the span of ZONE_NORMAL, there can't
be an overlap between ZONE_NORMAL and ZONE_MOVABLE.

Remove overlap_memmap_init().

Co-developed-by: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
 mm/mm_init.c | 24 ------------------------
 1 file changed, 24 deletions(-)

diff --git a/mm/mm_init.c b/mm/mm_init.c
index dce9dc9f2302..6f0a71ccca30 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -783,28 +783,6 @@ void __meminit init_deferred_page(unsigned long pfn, int nid)
 	__init_deferred_page(pfn, nid);
 }
 
-/* If zone is ZONE_MOVABLE but memory is mirrored, it is an overlapped init */
-static bool __meminit
-overlap_memmap_init(unsigned long zone, unsigned long *pfn)
-{
-	static struct memblock_region *r __meminitdata;
-
-	if (mirrored_kernelcore && zone == ZONE_MOVABLE) {
-		if (!r || *pfn >= memblock_region_memory_end_pfn(r)) {
-			for_each_mem_region(r) {
-				if (*pfn < memblock_region_memory_end_pfn(r))
-					break;
-			}
-		}
-		if (*pfn >= memblock_region_memory_base_pfn(r) &&
-		    memblock_is_mirror(r)) {
-			*pfn = memblock_region_memory_end_pfn(r);
-			return true;
-		}
-	}
-	return false;
-}
-
 /*
  * Only struct pages that correspond to ranges defined by memblock.memory
  * are zeroed and initialized by going through __init_single_page() during
@@ -891,8 +869,6 @@ void __meminit memmap_init_range(unsigned long size, int nid, unsigned long zone
 		 * function.  They do not exist on hotplugged memory.
 		 */
 		if (context == MEMINIT_EARLY) {
-			if (overlap_memmap_init(zone, &pfn))
-				continue;
 			if (defer_init(nid, pfn, zone_end_pfn)) {
 				deferred_struct_pages = true;
 				break;
-- 
2.53.0

Re: [PATCH 2/2] mm/mm_init: drop overlap_memmap_init()

[Wei Yang]

On Thu, Jun 25, 2026 at 10:39:40AM +0300, Mike Rapoport wrote:
>From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
>
>When ZONE_NORMAL and ZONE_MOVABLE could overlap because kernelcore=mirror
>didn't reduce the span of ZONE_NORMAL, initialization of the memory map had
>to skip overlapping pages during initialization of ZONE_MOVABLE to avoid
>double initialization of the same struct pages.
>
>Since kernelcore=mirror works now the same way as other variants of
>kernelcore=/movablecore=, and adjusts the span of ZONE_NORMAL, there can't
>be an overlap between ZONE_NORMAL and ZONE_MOVABLE.
>
>Remove overlap_memmap_init().
>

Hi, Mike

Do you think this is valuable to mention the double init for the overlapped
range?

>Co-developed-by: Wei Yang <richard.weiyang@gmail.com>
>Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
>Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
>---
> mm/mm_init.c | 24 ------------------------
> 1 file changed, 24 deletions(-)
>
>diff --git a/mm/mm_init.c b/mm/mm_init.c
>index dce9dc9f2302..6f0a71ccca30 100644
>--- a/mm/mm_init.c
>+++ b/mm/mm_init.c
>@@ -783,28 +783,6 @@ void __meminit init_deferred_page(unsigned long pfn, int nid)
> 	__init_deferred_page(pfn, nid);
> }
> 
>-/* If zone is ZONE_MOVABLE but memory is mirrored, it is an overlapped init */
>-static bool __meminit
>-overlap_memmap_init(unsigned long zone, unsigned long *pfn)
>-{
>-	static struct memblock_region *r __meminitdata;
>-
>-	if (mirrored_kernelcore && zone == ZONE_MOVABLE) {
>-		if (!r || *pfn >= memblock_region_memory_end_pfn(r)) {
>-			for_each_mem_region(r) {
>-				if (*pfn < memblock_region_memory_end_pfn(r))
>-					break;
>-			}
>-		}
>-		if (*pfn >= memblock_region_memory_base_pfn(r) &&
>-		    memblock_is_mirror(r)) {
>-			*pfn = memblock_region_memory_end_pfn(r);
>-			return true;
>-		}
>-	}
>-	return false;
>-}
>-
> /*
>  * Only struct pages that correspond to ranges defined by memblock.memory
>  * are zeroed and initialized by going through __init_single_page() during
>@@ -891,8 +869,6 @@ void __meminit memmap_init_range(unsigned long size, int nid, unsigned long zone
> 		 * function.  They do not exist on hotplugged memory.
> 		 */
> 		if (context == MEMINIT_EARLY) {
>-			if (overlap_memmap_init(zone, &pfn))
>-				continue;
> 			if (defer_init(nid, pfn, zone_end_pfn)) {
> 				deferred_struct_pages = true;
> 				break;
>-- 
>2.53.0

-- 
Wei Yang
Help you, Help me

Re: [PATCH 1/2] mm/mm_init: don't overlap NORMAL and MOVABLE zones with kernelcore=mirror

[David Hildenbrand (Arm)]

On 6/25/26 09:39, Mike Rapoport wrote:
> From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
> 
> When kernelcore or movablecore kernel parameters define size of the
> NORMAL and MOVABLE zones as percents of the total memory or by absolute
> value, ZONE_NORMAL is clamped at the beginning of ZONE_MOVABLE.
> 
> However, when kernelcore=mirror the ZONE_NORMAL span is not changed but
> rather pages from ZONE_MOVABLE counted as absent in ZONE_NORMAL.
> 
> Make the behaviour of kernelcore= parameter uniform and treat mirror
> just as another way to size the zones.

That sounds just about right to me.

Hard to imagine that any code would have relied on the old behavior.


Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David

Re: [PATCH 2/2] mm/mm_init: drop overlap_memmap_init()

[David Hildenbrand (Arm)]

On 6/25/26 09:39, Mike Rapoport wrote:
> From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
> 
> When ZONE_NORMAL and ZONE_MOVABLE could overlap because kernelcore=mirror
> didn't reduce the span of ZONE_NORMAL, initialization of the memory map had
> to skip overlapping pages during initialization of ZONE_MOVABLE to avoid
> double initialization of the same struct pages.
> 
> Since kernelcore=mirror works now the same way as other variants of
> kernelcore=/movablecore=, and adjusts the span of ZONE_NORMAL, there can't
> be an overlap between ZONE_NORMAL and ZONE_MOVABLE.
> 
> Remove overlap_memmap_init().
> 
> Co-developed-by: Wei Yang <richard.weiyang@gmail.com>
> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---

Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David

Re: [PATCH 2/2] mm/mm_init: drop overlap_memmap_init()

[Mike Rapoport]

Hi Wei,

On Thu, Jun 25, 2026 at 09:58:47AM +0000, Wei Yang wrote:
> On Thu, Jun 25, 2026 at 10:39:40AM +0300, Mike Rapoport wrote:
> >From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
> >
> >When ZONE_NORMAL and ZONE_MOVABLE could overlap because kernelcore=mirror
> >didn't reduce the span of ZONE_NORMAL, initialization of the memory map had
> >to skip overlapping pages during initialization of ZONE_MOVABLE to avoid
> >double initialization of the same struct pages.
> >
> >Since kernelcore=mirror works now the same way as other variants of
> >kernelcore=/movablecore=, and adjusts the span of ZONE_NORMAL, there can't
> >be an overlap between ZONE_NORMAL and ZONE_MOVABLE.
> >
> >Remove overlap_memmap_init().
> >
> 
> Do you think this is valuable to mention the double init for the overlapped
> range?

Not sure I follow.
We had this weird overlap_memmap_init() exactly to avoid double init.
 
> >Co-developed-by: Wei Yang <richard.weiyang@gmail.com>
> >Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> >Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> >---
> > mm/mm_init.c | 24 ------------------------
> > 1 file changed, 24 deletions(-)
> >
> >diff --git a/mm/mm_init.c b/mm/mm_init.c
> >index dce9dc9f2302..6f0a71ccca30 100644
> >--- a/mm/mm_init.c
> >+++ b/mm/mm_init.c
> >@@ -783,28 +783,6 @@ void __meminit init_deferred_page(unsigned long pfn, int nid)
> > 	__init_deferred_page(pfn, nid);
> > }
> > 
> >-/* If zone is ZONE_MOVABLE but memory is mirrored, it is an overlapped init */
> >-static bool __meminit
> >-overlap_memmap_init(unsigned long zone, unsigned long *pfn)
> >-{
> >-	static struct memblock_region *r __meminitdata;
> >-
> >-	if (mirrored_kernelcore && zone == ZONE_MOVABLE) {
> >-		if (!r || *pfn >= memblock_region_memory_end_pfn(r)) {
> >-			for_each_mem_region(r) {
> >-				if (*pfn < memblock_region_memory_end_pfn(r))
> >-					break;
> >-			}
> >-		}
> >-		if (*pfn >= memblock_region_memory_base_pfn(r) &&
> >-		    memblock_is_mirror(r)) {
> >-			*pfn = memblock_region_memory_end_pfn(r);
> >-			return true;
> >-		}
> >-	}
> >-	return false;
> >-}
> >-
> > /*
> >  * Only struct pages that correspond to ranges defined by memblock.memory
> >  * are zeroed and initialized by going through __init_single_page() during
> >@@ -891,8 +869,6 @@ void __meminit memmap_init_range(unsigned long size, int nid, unsigned long zone
> > 		 * function.  They do not exist on hotplugged memory.
> > 		 */
> > 		if (context == MEMINIT_EARLY) {
> >-			if (overlap_memmap_init(zone, &pfn))
> >-				continue;
> > 			if (defer_init(nid, pfn, zone_end_pfn)) {
> > 				deferred_struct_pages = true;
> > 				break;
> >-- 
> >2.53.0
> 
> -- 
> Wei Yang
> Help you, Help me

-- 
Sincerely yours,
Mike.

Re: [PATCH 0/2] mm/mm_init: don't overlap zones with kernelcore=mirror

[Mike Rapoport]

On Thu, Jun 25, 2026 at 10:39:38AM +0300, Mike Rapoport wrote:
> From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
> 
> Hi,
> 
> These patches make the behaviour of kernelcore= parameter uniform and
> treat mirror just as another way to size the zones and cleanup a weird
> part of the memory map initialization.

I'm queueing it for now in the memblock tree, will properly push after
merge window is closed.
    
> Mike Rapoport (Microsoft) (2):
>   mm/mm_init: don't overlap NORMAL and MOVABLE zones with kernelcore=mirror
>   mm/mm_init: drop overlap_memmap_init()
> 
>  mm/mm_init.c | 60 +++-------------------------------------------------
>  1 file changed, 3 insertions(+), 57 deletions(-)
> 
> 
> base-commit: 4549871118cf616eecdd2d939f78e3b9e1dddc48
> -- 
> 2.53.0
> 

-- 
Sincerely yours,
Mike.

Re: [PATCH 2/2] mm/mm_init: drop overlap_memmap_init()

[Wei Yang]

On Fri, Jun 26, 2026 at 10:40:32AM +0300, Mike Rapoport wrote:
>Hi Wei,
>
>On Thu, Jun 25, 2026 at 09:58:47AM +0000, Wei Yang wrote:
>> On Thu, Jun 25, 2026 at 10:39:40AM +0300, Mike Rapoport wrote:
>> >From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
>> >
>> >When ZONE_NORMAL and ZONE_MOVABLE could overlap because kernelcore=mirror
>> >didn't reduce the span of ZONE_NORMAL, initialization of the memory map had
>> >to skip overlapping pages during initialization of ZONE_MOVABLE to avoid
>> >double initialization of the same struct pages.
>> >
>> >Since kernelcore=mirror works now the same way as other variants of
>> >kernelcore=/movablecore=, and adjusts the span of ZONE_NORMAL, there can't
>> >be an overlap between ZONE_NORMAL and ZONE_MOVABLE.
>> >
>> >Remove overlap_memmap_init().
>> >
>> 
>> Do you think this is valuable to mention the double init for the overlapped
>> range?
>
>Not sure I follow.
>We had this weird overlap_memmap_init() exactly to avoid double init.
> 

Yes, this is really weird.

As I described the detail in [1], before this change kernel would have
overlapped zone range like:

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

Which means [140000, 1c0000] belongs to both Normal and Movable.
And memmap_init_range() would be called on this range twice for Normal and
Movable respectively. And we want overlap_memmap_init() could skip init this
to Normal. Because actually, the memory in this range belongs to Movable Zone.

But overlap_memmap_init() only would skip for Zone Movable. This means when
init to Zone Normal, it doesn't skip as we want. And when init to Zone
Movable, we don't expect it to skip.

[1]: https://lore.kernel.org/linux-mm/20260623092351.13031-3-richard.weiyang@gmail.com/

-- 
Wei Yang
Help you, Help me