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mm/hugetlb: keep max_huge_pages when dissolving surplus folios

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dissolve_free_hugetlb_folio() can remove a free folio as surplus when its
node has surplus pages.  In that case remove_hugetlb_folio() decrements
both nr_huge_pages and surplus_huge_pages, leaving the persistent pool
size unchanged.

Updating max_huge_pages as if a persistent folio had been removed can
therefore corrupt the persistent pool target and underflow it when
max_huge_pages is zero.  Keep max_huge_pages unchanged for surplus folios,
including the vmemmap restoration rollback path.

Link: https://lore.kernel.org/20260814083027.1419487-1-xialonglong2025@163.com
Fixes: cb402bbdab ("mm/hugetlb: fix surplus pages in dissolve_free_huge_page()")
Assisted-by: Codex:gpt-5.6-sol
Signed-off-by: Longlong Xia <xialonglong@kylinos.cn>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jinjiang Tu <tujinjiang@huawei.com>
Cc: Longlong Xia <xialonglong@kylinos.cn>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Longlong Xia
2026-08-14 16:30:27 +08:00
committed by Andrew Morton
parent dc41e961a2
commit 267bede12d
1 changed files with 4 additions and 2 deletions
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6
mm/hugetlb.c
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@@ -1992,7 +1992,8 @@ int dissolve_free_hugetlb_folio(struct folio *folio)
if (h->surplus_huge_pages_node[folio_nid(folio)])
adjust_surplus = true;
remove_hugetlb_folio(h, folio, adjust_surplus);
h->max_huge_pages--;
if (!adjust_surplus)
h->max_huge_pages--;
spin_unlock_irq(&hugetlb_lock);
/*
@@ -2012,7 +2013,8 @@ int dissolve_free_hugetlb_folio(struct folio *folio)
if (rc) {
spin_lock_irq(&hugetlb_lock);
add_hugetlb_folio(h, folio, adjust_surplus);
h->max_huge_pages++;
if (!adjust_surplus)
h->max_huge_pages++;
goto out;
}
} else {