Re: [PATCH v4 1/2] mm: move overlap memory map init check to memmap_init()

[Mike Rapoport <rppt@kernel.org>]

Hi,

On Tue, Apr 21, 2026 at 08:55:07AM -0400, Yuan Liu wrote:
> Move the overlap memmap init check from memmap_init_range() into
> memmap_init().
> 
> When mirrored kernelcore is enabled, avoid memory map initialization
> for overlap regions. There are two cases that may overlap: a mirror
> memory region assigned to movable zone, or a non-mirror memory region
> assigned to a non-movable zone but falling within the movable zone
> range.
> 
> Signed-off-by: Yuan Liu <yuan1.liu@intel.com>
> ---
>  mm/mm_init.c | 37 +++++++++++++------------------------
>  1 file changed, 13 insertions(+), 24 deletions(-)
> 
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index df34797691bd..2b5233060504 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -797,28 +797,6 @@ void __meminit reserve_bootmem_region(phys_addr_t start,
>  	}
>  }
>  
> -/* 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;
> -
> -	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
> @@ -905,8 +883,6 @@ 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;
> @@ -971,6 +947,7 @@ static void __init memmap_init(void)
>  
>  	for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, &nid) {
>  		struct pglist_data *node = NODE_DATA(nid);
> +		struct memblock_region *r = &memblock.memory.regions[i];

Please move this declaration above struct pglist_data, let's keep reverse
xmas tree where possible.
>  
>  		for (j = 0; j < MAX_NR_ZONES; j++) {
>  			struct zone *zone = node->node_zones + j;
> @@ -978,6 +955,18 @@ static void __init memmap_init(void)
>  			if (!populated_zone(zone))
>  				continue;
>  
> +			if (mirrored_kernelcore) {
> +				const bool is_mirror = memblock_is_mirror(r);
> +				const bool is_movable_zone = (j == ZONE_MOVABLE);
> +
> +				if (is_mirror && is_movable_zone)
> +					continue;
> +
> +				if (!is_mirror && !is_movable_zone &&
> +				    start_pfn >= zone_movable_pfn[nid])
> +					continue;
> +			}
> +

I think this:

			if (mirrored_kernelcore && j == ZONE_MOVABLE &&
			    memblock_is_mirror(r))
				continue;

would be enough to remove overlap_memmap_init() and keep the existing
logic.

I wouldn't deal the theoretical cases Wei mentioned in this thread for
now and prefer to keep the things simple. 
The assumptions that mirrored memory spans a contiguous range below some
limit and that mirrored memory is not removable existed for years and I
don't see why we should change the logic now and complicate the code for
exotic theoretical memory layouts.

>  			memmap_init_zone_range(zone, start_pfn, end_pfn,
>  					       &hole_pfn);
>  			zone_id = j;
> -- 
> 2.47.3
> 

-- 
Sincerely yours,
Mike.