On 09.10.25 10:04, Christophe Leroy wrote:
Le 09/10/2025 à 09:22, David Hildenbrand a écrit :
On 09.10.25 09:14, Christophe Leroy wrote:
Hi David,
Le 01/09/2025 à 17:03, David Hildenbrand a écrit :
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 1e777cc51ad04..d3542e92a712e 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4657,6 +4657,7 @@ static int __init hugetlb_init(void) BUILD_BUG_ON(sizeof_field(struct page, private) * BITS_PER_BYTE < __NR_HPAGEFLAGS); + BUILD_BUG_ON_INVALID(HUGETLB_PAGE_ORDER > MAX_FOLIO_ORDER); if (!hugepages_supported()) { if (hugetlb_max_hstate || default_hstate_max_huge_pages) @@ -4740,6 +4741,7 @@ void __init hugetlb_add_hstate(unsigned int order) } BUG_ON(hugetlb_max_hstate >= HUGE_MAX_HSTATE); BUG_ON(order < order_base_2(__NR_USED_SUBPAGE)); + WARN_ON(order > MAX_FOLIO_ORDER); h = &hstates[hugetlb_max_hstate++]; __mutex_init(&h->resize_lock, "resize mutex", &h->resize_key); h->order = order;
We end up registering hugetlb folios that are bigger than MAX_FOLIO_ORDER. So we have to figure out how a config can trigger that (and if we have to support that).
MAX_FOLIO_ORDER is defined as:
#ifdef CONFIG_ARCH_HAS_GIGANTIC_PAGE #define MAX_FOLIO_ORDER PUD_ORDER #else #define MAX_FOLIO_ORDER MAX_PAGE_ORDER #endif
MAX_PAGE_ORDER is the limit for dynamic creation of hugepages via /sys/kernel/mm/hugepages/ but bigger pages can be created at boottime with kernel boot parameters without CONFIG_ARCH_HAS_GIGANTIC_PAGE:
hugepagesz=64m hugepages=1 hugepagesz=256m hugepages=1Gives:
HugeTLB: registered 1.00 GiB page size, pre-allocated 0 pages HugeTLB: 0 KiB vmemmap can be freed for a 1.00 GiB page HugeTLB: registered 64.0 MiB page size, pre-allocated 1 pages HugeTLB: 0 KiB vmemmap can be freed for a 64.0 MiB page HugeTLB: registered 256 MiB page size, pre-allocated 1 pages HugeTLB: 0 KiB vmemmap can be freed for a 256 MiB page HugeTLB: registered 4.00 MiB page size, pre-allocated 0 pages HugeTLB: 0 KiB vmemmap can be freed for a 4.00 MiB page HugeTLB: registered 16.0 MiB page size, pre-allocated 0 pages HugeTLB: 0 KiB vmemmap can be freed for a 16.0 MiB page
I think it's a violation of CONFIG_ARCH_HAS_GIGANTIC_PAGE. The existing folio_dump() code would not handle it correctly as well.
See how snapshot_page() uses MAX_FOLIO_NR_PAGES.