Le 09/10/2025 à 10:14, David Hildenbrand a écrit :
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=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
I think it's a violation of CONFIG_ARCH_HAS_GIGANTIC_PAGE. The existing
folio_dump() code would not handle it correctly as well.
I'm trying to dig into history and when looking at commit 4eb0716e868e
("hugetlb: allow to free gigantic pages regardless of the
configuration") I understand that CONFIG_ARCH_HAS_GIGANTIC_PAGE is
needed to be able to allocate gigantic pages at runtime. It is not
needed to reserve gigantic pages at boottime.
What am I missing ?
See how snapshot_page() uses MAX_FOLIO_NR_PAGES.
