RE: [PATCH v5 1/5] mm: move mirrored memory overlap checking to the outer loop

[Liu, Yuan1]

> -----Original Message-----
> From: Wei Yang <richard.weiyang@xxxxxxxxx>
> Sent: Monday, May 25, 2026 4:36 PM
> To: Liu, Yuan1 <yuan1.liu@xxxxxxxxx>
> Cc: Wei Yang <richard.weiyang@xxxxxxxxx>; David Hildenbrand
> <david@xxxxxxxxxx>; Oscar Salvador <osalvador@xxxxxxx>; Mike Rapoport
> <rppt@xxxxxxxxxx>; 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>; Zeng, Jason <jason.zeng@xxxxxxxxx>; linux-
> kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v5 1/5] mm: move mirrored memory overlap checking to
> the outer loop
> 
> On Fri, May 22, 2026 at 07:43:38AM +0000, Liu, Yuan1 wrote:
> >> Subject: Re: [PATCH v5 1/5] mm: move mirrored memory overlap checking
> to
> >> the outer loop
> >>
> >> On Wed, May 20, 2026 at 05:34:53AM -0400, Yuan Liu wrote:
> >> >Move the overlap memmap initialization check from memmap_init_range()
> >> >to memmap_init(), and replace the per-PFN check with a memblock-based
> >> >check.
> >>
> >> The description is a little simple.
> >>
> >> Even I know the purpose, I feel confused at the first glance.
> >
> >Thanks for the review.
> >I will try to rephrase it and provide a clearer description in the next
> version.
> >
> >> >
> >> >Reviewed-by: Wei Yang <richard.weiyang@xxxxxxxxx>
> >> >Reviewed-by: Jason Zeng <jason.zeng@xxxxxxxxx>
> >> >Signed-off-by: Yuan Liu <yuan1.liu@xxxxxxxxx>
> >> >---
> >> > mm/mm_init.c | 29 +++++------------------------
> >> > 1 file changed, 5 insertions(+), 24 deletions(-)
> >> >
> >> >diff --git a/mm/mm_init.c b/mm/mm_init.c
> >> >index f9f8e1af921c..24e103a402b0 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;
> >> >@@ -956,6 +932,7 @@ static void __init memmap_init(void)
> >> > 	int i, j, zone_id = 0, nid;
> >> >
> >> > 	for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, &nid)
> >> {
> >> >+		struct memblock_region *r = &memblock.memory.regions[i];
> >> > 		struct pglist_data *node = NODE_DATA(nid);
> >> >
> >> > 		for (j = 0; j < MAX_NR_ZONES; j++) {
> >> >@@ -964,6 +941,10 @@ static void __init memmap_init(void)
> >> > 			if (!populated_zone(zone))
> >> > 				continue;
> >> >
> >> >+			if (mirrored_kernelcore && j == ZONE_MOVABLE &&
> >> >+			    memblock_is_mirror(r))
> >> >+				continue;
> >> >+
> >>
> >> So you have figured out the memory layout of mirror memory?
> >>
> >> Would you mind elaborate?
> >
> >I have a Xeon server, collected mirror memory layout information as below
> by using follow changes:
> >
> >int __init_memblock memblock_mark_mirror(phys_addr_t base, phys_addr_t
> size)
> > {
> >-       if (!mirrored_kernelcore)
> >+       int ret;
> >+       phys_addr_t end = base + size - 1;
> >+
> >+       pr_info("memblock_mark_mirror: base=%pa, size=%pa,
> mirrored_kernelcore=%d\n",
> >+               &base, &size, mirrored_kernelcore);
> >+
> >+       if (!mirrored_kernelcore) {
> >+               pr_info("memblock_mark_mirror: mirrored_kernelcore not
> enabled, skipping\n");
> >                return 0;
> >+       }
> >
> >        system_has_some_mirror = true;
> >
> >-       return memblock_setclr_flag(&memblock.memory, base, size, 1,
> MEMBLOCK_MIRROR);
> >+       ret = memblock_setclr_flag(&memblock.memory, base, size, 1,
> MEMBLOCK_MIRROR);
> >+       pr_info("memblock_mark_mirror: marked [%pa-%pa] as MIRROR,
> ret=%d\n",
> >+               &base, &end, ret);
> >+       return ret;
> > }
> >
> >Here is the detailed layout information:
> >
> 
> Thanks for the detailed output.
> 
> After some investigation, I got two things to discuss here:
> 
>   * current mirror memory would disable memmap defer init
>   * confirm the mirror memory layout and may simplify handling
> 
> Before discussion, let me mark the key point in the output below.
> 
> >Case 1: efibootmgr -m t -M 0
> >Enable mirror memory below 4GB, and no mirror memory above 4G
> >
> >=== zoneinfo summary ===
> >node   zone       start_pfn    end_pfn      start_addr         end_addr
> >------ ---------- ------------ ------------ ------------------ ----------
> ---
> >0      DMA        0x1          0xfff        0x1000             0xffffff
> >0      DMA32      0x1000       0xfffff      0x1000000          0xffffffff
> >0      Normal     0x100000     0x7fbffff    0x100000000
> 0x7fbfffffff
> >0      Movable    0x140000     0x7fbffff    0x140000000
> 0x7fbfffffff
> 
> (1) Normal and Movable zone end with the same address, so overlapped.
> 
> >1      Normal     0x7fc0000    0xff7ffff    0x7fc0000000
> 0xff7fffffff
> >1      Movable    0x8000000    0xff7ffff    0x8000000000
> 0xff7fffffff
> 
> The same as (1).
> 
> >
> >node  start                end                  size              flags
> mirror   pfn_range
> >----  -------------------- -------------------- ------------ ------------
> --- -------- ------------------
> >0     0x0000000000001000   0x000000000009dfff   0x000000000009d000 0x2
> yes      0x1-0x9e
> >0     0x000000000009f000   0x000000000009ffff   0x0000000000001000 0x2
> yes      0x9f-0xa0
> >0     0x0000000000100000   0x0000000066416fff   0x0000000066317000 0x2
> yes      0x100-0x66417
> >0     0x00000000777ff000   0x00000000777fffff   0x0000000000001000 0x2
> yes      0x777ff-0x77800
> >0     0x0000000100000000   0x000000013fffffff   0x0000000040000000 0x2
> yes      0x100000-0x140000
> 
> (2) You mentioned no mirror memory above 4G. If my understanding is
> correct, 4G's
> address is 0x100000000. So why this range is marked mirror? Is there some
> limitation for this?

Hi Wei

efibootmgr enables mirror memory below 4 GB through the -m (--mirror-below-4G)
option, and configures the percentage of memory to be mirrored above 4 GB through
the -M (--mirror-above-4G) option.

My understanding is that the layout of mirrored memory is determined by the BIOS.