linux-kernel - [PATCH] mm: fix accounting of memmap pages for early sections

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Message-ID: <20250804090859.727207-1-sumanthk@linux.ibm.com>
Date: Mon,  4 Aug 2025 11:08:59 +0200
From: Sumanth Korikkar <sumanthk@...ux.ibm.com>
To: Andrew Morton <akpm@...ux-foundation.org>, linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        David Hildenbrand <david@...hat.com>
Cc: Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        linux-s390 <linux-s390@...r.kernel.org>, sumanthk@...ux.ibm.com
Subject: [PATCH] mm: fix accounting of memmap pages for early sections

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 also decrements the count of nr_memmap_pages.

* For pages from the boot allocator, free_map_bootmem() is called. But
  it currently does not adjust the nr_memmap_boot_pages.

To fix this inconsistency, update free_map_bootmem() to also decrement
the nr_memmap_boot_pages count by invoking memmap_boot_pages_add(),
mirroring how free_vmemmap_page() handles this for boot-allocated pages.

This ensures correct tracking of memmap pages regardless of allocation
source.

Cc: stable@...r.kernel.org
Fixes: 15995a352474 ("mm: report per-page metadata information")
Signed-off-by: Sumanth Korikkar <sumanthk@...ux.ibm.com>
---
 mm/sparse.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/sparse.c b/mm/sparse.c
index 3c012cf83cc2..d7c128015397 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -688,6 +688,7 @@ static void free_map_bootmem(struct page *memmap)
 	unsigned long start = (unsigned long)memmap;
 	unsigned long end = (unsigned long)(memmap + PAGES_PER_SECTION);

+	memmap_boot_pages_add(-1L * (DIV_ROUND_UP(end - start, PAGE_SIZE)));
 	vmemmap_free(start, end, NULL);
 }

-- 
2.48.1