On Wed, Jul 14, 2021 at 03:32:08PM -0700, Andrew Morton wrote:

On Wed, 14 Jul 2021 15:37:38 +0300 Mike Rapoport [off-list ref] wrote:

quoted

From: Mike Rapoport <redacted>

There are several places that allocate memory for the memory map:
alloc_node_mem_map() for FLATMEM, sparse_buffer_init() and
__populate_section_memmap() for SPARSEMEM.

The memory allocated in the FLATMEM case is zeroed and it is never
poisoned, regardless of CONFIG_PAGE_POISON setting.

The memory allocated in the SPARSEMEM cases is not zeroed and it is
implicitly poisoned inside memblock if CONFIG_PAGE_POISON is set.

Introduce memmap_alloc() wrapper for memblock allocators that will be used
for both FLATMEM and SPARSEMEM cases and will makei memory map zeroing and
poisoning consistent for different memory models.

...

--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c

@@ -6730,6 +6730,26 @@ static void __init memmap_init(void)
 		init_unavailable_range(hole_pfn, end_pfn, zone_id, nid);
 }
 
+void __init *memmap_alloc(phys_addr_t size, phys_addr_t align,
+			  phys_addr_t min_addr, int nid, bool exact_nid)
+{
+	void *ptr;
+
+	if (exact_nid)
+		ptr = memblock_alloc_exact_nid_raw(size, align, min_addr,
+						   MEMBLOCK_ALLOC_ACCESSIBLE,
+						   nid);
+	else
+		ptr = memblock_alloc_try_nid_raw(size, align, min_addr,
+						 MEMBLOCK_ALLOC_ACCESSIBLE,
+						 nid);
+
+	if (ptr && size > 0)
+		page_init_poison(ptr, size);
+
+	return ptr;
+}
+
 static int zone_batchsize(struct zone *zone)
 {
 #ifdef CONFIG_MMU

@@ -7501,8 +7521,8 @@ static void __ref alloc_node_mem_map(struct pglist_data *pgdat)
 		end = pgdat_end_pfn(pgdat);
 		end = ALIGN(end, MAX_ORDER_NR_PAGES);
 		size =  (end - start) * sizeof(struct page);
-		map = memblock_alloc_node(size, SMP_CACHE_BYTES,
-					  pgdat->node_id);
+		map = memmap_alloc(size, SMP_CACHE_BYTES, MEMBLOCK_LOW_LIMIT,
+				   pgdat->node_id, false);

Mostly offtopic, but...  Why is alloc_node_mem_map() marked __ref? 

Once free_area_init_node() was __meminit, I stopped digging at that point.

afaict it can be __init?

Yes.

-- 
Sincerely yours,
Mike.