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

[Liu, Yuan1]

> Subject: Re: [PATCH v4 1/2] mm: move overlap memory map init check to
> memmap_init()
> 
> 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@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];
> 
> Please move this declaration above struct pglist_data, let's keep reverse
> xmas tree where possible.

Sure, I will refine this next version.

> >
> >  		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.

Hi Mike

Thank you for your comments. 
I will update the next version based on your suggestions.
 
> >  			memmap_init_zone_range(zone, start_pfn, end_pfn,
> >  					       &hole_pfn);
> >  			zone_id = j;
> > --
> > 2.47.3
> >
> 
> --
> Sincerely yours,
> Mike.