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

[Wei Yang]

On Sat, Apr 25, 2026 at 11:01:42AM +0200, Mike Rapoport wrote:
[...]
>>  
>>  		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;
>> +			}
>> +
>

Hi, Mike

Thanks for your review.

>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. 

That would be great to keep 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.
>

I don't follow here. Still not clear what the memory layout should be.

IIUC, case C is not real, but case A/B are.

I took case B as an example and do some tests. Below is my finding.

Here is memblock layout for case B, with the head 1G of ZONE_NORMAL is mirror
memory.

   MEMBLOCK configuration:
    memory size = 0x000000017ff7dc00 reserved size = 0x0000000005a939c2
    memory.cnt  = 0x4
    memory[0x0]     [0x0000000000001000-0x000000000009efff], node 0 flags: 0x2
    memory[0x1]     [0x0000000000100000-0x00000000bffdefff], node 0 flags: 0x2
    memory[0x2]     [0x0000000100000000-0x000000013fffffff], node 1 flags: 0x2
    memory[0x3]     [0x0000000140000000-0x00000001bfffffff], node 1 flags: 0x0

This meets:

  * mirrored memory span from low to 0x13fffffff

Then I add below change along with your suggested change.

@@ -964,6 +964,8 @@ static void __init memmap_init_zone_range(struct zone *zone,
        if (start_pfn >= end_pfn)
                return;

+       pr_info(" [%lx, %lx] init to %s\n",
+                       start_pfn, end_pfn, zone->name);
        memmap_init_range(end_pfn - start_pfn, nid, zone_id, start_pfn,
                          zone_end_pfn, MEMINIT_EARLY, NULL, MIGRATE_MOVABLE,
                          false);

And see the last normal memory range is initialized twice.

 [140000, 1c0000] init to Normal
 [140000, 1c0000] init to Movable

Then I removed your suggested change and adjust code like below.

@@ -954,6 +954,7 @@ static void __init memmap_init_zone_range(struct zone *zone,
                                          unsigned long end_pfn,
                                          unsigned long *hole_pfn)
 {
+       unsigned long old_start = start_pfn, old_end = end_pfn;
        unsigned long zone_start_pfn = zone->zone_start_pfn;
        unsigned long zone_end_pfn = zone_start_pfn + zone->spanned_pages;
        int nid = zone_to_nid(zone), zone_id = zone_idx(zone);
,
        start_pfn = clamp(start_pfn, zone_start_pfn, zone_end_pfn);
        end_pfn = clamp(end_pfn, zone_start_pfn, zone_end_pfn);

-       if (start_pfn >= end_pfn)
+       if (start_pfn >= end_pfn) {
+               pr_info(" [%lx, %lx] skipped to %s\n",
+                       old_start, old_end, zone->name);
                return;
+       }

+       pr_info(" [%lx, %lx] init to %s\n",
+                       start_pfn, end_pfn, zone->name);
        memmap_init_range(end_pfn - start_pfn, nid, zone_id, start_pfn,
                          zone_end_pfn, MEMINIT_EARLY, NULL, MIGRATE_MOVABLE,
                          false);

This shows current code already could skip the mirror range to ZONE_MOVABLE
for this kind memory layout, since ZONE_MOVABLE doesn't span to it.

  [100000, 140000] skipped to Movable
  [140000, 1c0000] init to Normal
  [140000, 1c0000] init to Movable

So I am not sure the real mirrored memory layout could be. Would you mind
giving more detail to help me get on the right track?

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

-- 
Wei Yang
Help you, Help me