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

[Liu, Yuan1]

> -----Original Message-----
> From: Wei Yang <richard.weiyang@xxxxxxxxx>
> Sent: Wednesday, April 22, 2026 9:11 AM
> To: Liu, Yuan1 <yuan1.liu@xxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>; Oscar Salvador
> <osalvador@xxxxxxx>; Mike Rapoport <rppt@xxxxxxxxxx>; Wei Yang
> <richard.weiyang@xxxxxxxxx>; linux-mm@xxxxxxxxx; Hu, Yong
> <yong.hu@xxxxxxxxx>; Zou, Nanhai <nanhai.zou@xxxxxxxxx>; Tim Chen
> <tim.c.chen@xxxxxxxxxxxxxxx>; Zhuo, Qiuxu <qiuxu.zhuo@xxxxxxxxx>; Chen, Yu
> C <yu.c.chen@xxxxxxxxx>; Deng, Pan <pan.deng@xxxxxxxxx>; Li, Tianyou
> <tianyou.li@xxxxxxxxx>; Chen Zhang <zhangchen.kidd@xxxxxx>; linux-
> kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v4 1/2] mm: move overlap memory map init check to
> memmap_init()
> 
> 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@xxxxxxxxx>
> >---
> > 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];
> >
> > 		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;
> 
> IIUC, when mirrored_kernelcore is set but !memblock_has_mirror() or
> is_kdump_kernel(), zone_movable_pfn[nid] is kept to be 0.
> 
> This means it will skip all memory regions.

You're right. I verified the case you mentioned that mirrored_kernelcore
is enabled but there are no mirrored memory blocks, it indeed has a problem. 

Thank you very much for pointing that out.

> >+			}
> >+
> > 			memmap_init_zone_range(zone, start_pfn, end_pfn,
> > 					       &hole_pfn);
> > 			zone_id = j;
> >--
> >2.47.3
> 
> --
> Wei Yang
> Help you, Help me