Le 14/11/2025 à 22:49, David Hildenbrand (Red Hat) a écrit :
In the past, CONFIG_ARCH_HAS_GIGANTIC_PAGE indicated that we support
runtime allocation of gigantic hugetlb folios. In the meantime it evolved
into a generic way for the architecture to state that it supports
gigantic hugetlb folios.
In commit fae7d834c43c ("mm: add __dump_folio()") we started using
CONFIG_ARCH_HAS_GIGANTIC_PAGE to decide MAX_FOLIO_ORDER: whether we could
have folios larger than what the buddy can handle. In the context of
that commit, we started using MAX_FOLIO_ORDER to detect page corruptions
when dumping tail pages of folios. Before that commit, we assumed that
we cannot have folios larger than the highest buddy order, which was
obviously wrong.
In commit 7b4f21f5e038 ("mm/hugetlb: check for unreasonable folio sizes
when registering hstate"), we used MAX_FOLIO_ORDER to detect
inconsistencies, and in fact, we found some now.
Powerpc allows for configs that can allocate gigantic folio during boot
(not at runtime), that do not set CONFIG_ARCH_HAS_GIGANTIC_PAGE and can
exceed PUD_ORDER.
To fix it, let's make powerpc select CONFIG_ARCH_HAS_GIGANTIC_PAGE with
hugetlb on powerpc, and increase the maximum folio size with hugetlb to 16
GiB on 64bit (possible on arm64 and powerpc) and 1 GiB on 32 bit (powerpc).
Note that on some powerpc configurations, whether we actually have gigantic
pages depends on the setting of CONFIG_ARCH_FORCE_MAX_ORDER, but there is
nothing really problematic about setting it unconditionally: we just try to
keep the value small so we can better detect problems in __dump_folio()
and inconsistencies around the expected largest folio in the system.
Ideally, we'd have a better way to obtain the maximum hugetlb folio size
and detect ourselves whether we really end up with gigantic folios. Let's
defer bigger changes and fix the warnings first.
While at it, handle gigantic DAX folios more clearly: DAX can only
end up creating gigantic folios with HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD.
Add a new Kconfig option HAVE_GIGANTIC_FOLIOS to make both cases
clearer. In particular, worry about ARCH_HAS_GIGANTIC_PAGE only with
HUGETLB_PAGE.
Note: with enabling CONFIG_ARCH_HAS_GIGANTIC_PAGE on powerpc, we will now
also allow for runtime allocations of folios in some more powerpc configs.
I don't think this is a problem, but if it is we could handle it through
__HAVE_ARCH_GIGANTIC_PAGE_RUNTIME_SUPPORTED.
Reviewed-by: Christophe Leroy <[email protected]>
Tested on powerpc 8xx with CONFIG_ARCH_FORCE_MAX_ORDER=8 instead of 9.
It is now possible to add hugepages with the following command:
echo 4 > /sys/kernel/mm/hugepages/hugepages-8192kB/nr_hugepages
But only if CONFIG_CMA is set.
Tested-by: Christophe Leroy <[email protected]>
While __dump_page()/__dump_folio was also problematic (not handling dumping
of tail pages of such gigantic folios correctly), it doesn't seem
critical enough to mark it as a fix.
Fixes: 7b4f21f5e038 ("mm/hugetlb: check for unreasonable folio sizes when
registering hstate")
Reported-by: Christophe Leroy <[email protected]>
Closes:
https://lore.kernel.org/r/[email protected]/
Reported-by: Sourabh Jain <[email protected]>
Closes:
https://lore.kernel.org/r/[email protected]/
Cc: Andrew Morton <[email protected]>
Cc: Ritesh Harjani (IBM) <[email protected]>
Cc: Madhavan Srinivasan <[email protected]>
Cc: Donet Tom <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: "Liam R. Howlett" <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Nathan Chancellor <[email protected]>
Signed-off-by: David Hildenbrand (Red Hat) <[email protected]>
---
v1 -> v2:
* Adjust patch description (typo, 16G vs 1G)
* Remove ARCH_HAS_GIGANTIC_PAGE from arch/powerpc/platforms/Kconfig.cputype
* Mention CONFIG_HAVE_GIGANTIC_FOLIOS in comment
* Use 1 GiB on 32bit to avoid unsigned-long capacity issues
I yet have to boot-test this on 32bit powerpc. Something for Monday.
---
arch/powerpc/Kconfig | 1 +
arch/powerpc/platforms/Kconfig.cputype | 1 -
include/linux/mm.h | 13 ++++++++++---
mm/Kconfig | 7 +++++++
4 files changed, 18 insertions(+), 4 deletions(-)
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index e24f4d88885ae..9537a61ebae02 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -137,6 +137,7 @@ config PPC
select ARCH_HAS_DMA_OPS if PPC64
select ARCH_HAS_FORTIFY_SOURCE
select ARCH_HAS_GCOV_PROFILE_ALL
+ select ARCH_HAS_GIGANTIC_PAGE if ARCH_SUPPORTS_HUGETLBFS
select ARCH_HAS_KCOV
select ARCH_HAS_KERNEL_FPU_SUPPORT if PPC64 && PPC_FPU
select ARCH_HAS_MEMBARRIER_CALLBACKS
diff --git a/arch/powerpc/platforms/Kconfig.cputype
b/arch/powerpc/platforms/Kconfig.cputype
index 7b527d18aa5ee..4c321a8ea8965 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -423,7 +423,6 @@ config PPC_64S_HASH_MMU
config PPC_RADIX_MMU
bool "Radix MMU Support"
depends on PPC_BOOK3S_64
- select ARCH_HAS_GIGANTIC_PAGE
default y
help
Enable support for the Power ISA 3.0 Radix style MMU. Currently this
diff --git a/include/linux/mm.h b/include/linux/mm.h
index d16b33bacc32b..7c79b3369b82c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2074,7 +2074,7 @@ static inline unsigned long folio_nr_pages(const struct
folio *folio)
return folio_large_nr_pages(folio);
}
-#if !defined(CONFIG_ARCH_HAS_GIGANTIC_PAGE)
+#if !defined(CONFIG_HAVE_GIGANTIC_FOLIOS)
/*
* We don't expect any folios that exceed buddy sizes (and consequently
* memory sections).
@@ -2087,10 +2087,17 @@ static inline unsigned long folio_nr_pages(const struct
folio *folio)
* pages are guaranteed to be contiguous.
*/
#define MAX_FOLIO_ORDER PFN_SECTION_SHIFT
-#else
+#elif defined(CONFIG_HUGETLB_PAGE)
/*
* There is no real limit on the folio size. We limit them to the maximum we
- * currently expect (e.g., hugetlb, dax).
+ * currently expect (see CONFIG_HAVE_GIGANTIC_FOLIOS): with hugetlb, we expect
+ * no folios larger than 16 GiB on 64bit and 1 GiB on 32bit.
+ */
+#define MAX_FOLIO_ORDER get_order(IS_ENABLED(CONFIG_64BIT) ?
SZ_16G : SZ_1G)
+#else
+/*
+ * Without hugetlb, gigantic folios that are bigger than a single PUD are
+ * currently impossible.
*/
#define MAX_FOLIO_ORDER PUD_ORDER
#endif
diff --git a/mm/Kconfig b/mm/Kconfig
index 0e26f4fc8717b..ca3f146bc7053 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -908,6 +908,13 @@ config PAGE_MAPCOUNT
config PGTABLE_HAS_HUGE_LEAVES
def_bool TRANSPARENT_HUGEPAGE || HUGETLB_PAGE
+#
+# We can end up creating gigantic folio.
+#
+config HAVE_GIGANTIC_FOLIOS
+ def_bool (HUGETLB_PAGE && ARCH_HAS_GIGANTIC_PAGE) || \
+ (ZONE_DEVICE && HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)
+
# TODO: Allow to be enabled without THP
config ARCH_SUPPORTS_HUGE_PFNMAP
def_bool n
base-commit: 6146a0f1dfae5d37442a9ddcba012add260bceb0
