Le 09/10/2025 à 09:22, David Hildenbrand a écrit :

On 09.10.25 09:14, Christophe Leroy wrote:

quoted

Hi David,

Le 01/09/2025 à 17:03, David Hildenbrand a écrit :

quoted

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=1

Gives:

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


Christophe