[PATCH v2] mm: fix accounting of memmap pages for early sections

[Sumanth Korikkar <sumanthk@linux.ibm.com>]

memmap pages can be allocated either from the memblock (boot) allocator
during early boot or from the buddy allocator.

When these memmap pages are removed via arch_remove_memory(), the
deallocation path depends on their source:

* For pages from the buddy allocator, depopulate_section_memmap() is
  called, which should decrement the count of nr_memmap_pages.

* For pages from the boot allocator, free_map_bootmem() is called, which
  should decrement the count of the nr_memmap_boot_pages.

Ensure correct tracking of memmap pages for both early sections and non
early sections by adjusting the accounting in section_deactivate().

Cc: stable@vger.kernel.org
Fixes: 15995a352474 ("mm: report per-page metadata information")
Suggested-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
---
v2: consider accounting for !CONFIG_SPARSEMEM_VMEMMAP.

 mm/sparse.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/mm/sparse.c b/mm/sparse.c
index 3c012cf83cc2..b9cc9e548f80 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -680,7 +680,6 @@ static void depopulate_section_memmap(unsigned long pfn, unsigned long nr_pages,
 	unsigned long start = (unsigned long) pfn_to_page(pfn);
 	unsigned long end = start + nr_pages * sizeof(struct page);
 
-	memmap_pages_add(-1L * (DIV_ROUND_UP(end - start, PAGE_SIZE)));
 	vmemmap_free(start, end, altmap);
 }
 static void free_map_bootmem(struct page *memmap)
@@ -856,10 +855,14 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
 	 * The memmap of early sections is always fully populated. See
 	 * section_activate() and pfn_valid() .
 	 */
-	if (!section_is_early)
+	if (!section_is_early) {
+		memmap_pages_add(-1L * (DIV_ROUND_UP(nr_pages * sizeof(struct page), PAGE_SIZE)));
 		depopulate_section_memmap(pfn, nr_pages, altmap);
-	else if (memmap)
+	} else if (memmap) {
+		memmap_boot_pages_add(-1L * (DIV_ROUND_UP(nr_pages * sizeof(struct page),
+				      PAGE_SIZE)));
 		free_map_bootmem(memmap);
+	}
 
 	if (empty)
 		ms->section_mem_map = (unsigned long)NULL;
-- 
2.48.1