On 10.11.25 19:31, Christophe Leroy wrote:
Le 10/11/2025 à 12:27, David Hildenbrand (Red Hat) a écrit :
Thanks for the review!
So I think what you want instead is:
diff --git a/arch/powerpc/platforms/Kconfig.cputype
b/arch/powerpc/platforms/Kconfig.cputype
index 7b527d18aa5ee..1f5a1e587740c 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -276,6 +276,7 @@ config PPC_E500
select FSL_EMB_PERFMON
bool
select ARCH_SUPPORTS_HUGETLBFS if PHYS_64BIT || PPC64
+ select ARCH_HAS_GIGANTIC_PAGE if ARCH_SUPPORTS_HUGETLBFS
select PPC_SMP_MUXED_IPI
select PPC_DOORBELL
select PPC_KUEP
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
Should remain I think.
default y
help
Enable support for the Power ISA 3.0 Radix style MMU.
Currently
We also have PPC_8xx do a
select ARCH_SUPPORTS_HUGETLBFS
And of course !PPC_RADIX_MMU (e.g., PPC_64S_HASH_MMU) through
PPC_BOOK3S_64.
Are we sure they cannot end up with gigantic folios through hugetlb?
Yes indeed. My PPC_8xx is OK because I set CONFIG_ARCH_FORCE_MAX_ORDER=9
(largest hugepage is 8M) but I do get the warning with the default value
which is 8 (with 16k pages).
For PPC_64S_HASH_MMU, max page size is 16M, we get no warning with
CONFIG_ARCH_FORCE_MAX_ORDER=8 which is the default value but get the
warning with CONFIG_ARCH_FORCE_MAX_ORDER=7
Right, the dependency on CONFIG_ARCH_FORCE_MAX_ORDER is nasty. In the
future,
likely the arch should just tell us the biggest possible hugetlb size
and we
can then determine this ourselves.
... or we'll simply remove the gigantic vs. !gigantic handling
completely and
simply assume that "if there is hugetlb, we might have gigantic folios".
Should CONFIG_ARCH_HAS_GIGANTIC_PAGE be set unconditionaly as soon as
hugepages are selected, or should it depend on
CONFIG_ARCH_FORCE_MAX_ORDER ? What is the cost of selecting
CONFIG_ARCH_HAS_GIGANTIC_PAGE ?
There is no real cost, we just try to keep the value small so
__dump_folio()
can better detect inconsistencies.
To fix it for now, likely the following is good enough (pushed to the
previously mentioned branch):
From 7abf0f52e59d96533aa8c96194878e9453aa8be0 Mon Sep 17 00:00:00 2001
From: "David Hildenbrand (Red Hat)" <[email protected]>
Date: Thu, 6 Nov 2025 11:31:45 +0100
Subject: [PATCH] mm: fix MAX_FOLIO_ORDER on powerpc configs with hugetlb
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 (possible on arm64 and 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.
While __dump_page()/__dump_folio was also problematic (not handling
dumping
of tail pages of such gigantic folios correctly), it doesn't relevant
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://eur01.safelinks.protection.outlook.com/?
url=https%3A%2F%2Flore.kernel.org%2Fr%2F3e043453-3f27-48ad-b987-
cc39f523060a%40csgroup.eu%2F&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7Cb376c59325bf40bc08ce08de211479f4%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638984569012877144%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=KwQwqCg2Cu5oXXwBYhuQvW2kZqjyNZMk5N6zfsg%2FCHI%3D&reserved=0
Reported-by: Sourabh Jain <[email protected]>
Closes: https://eur01.safelinks.protection.outlook.com/?
url=https%3A%2F%2Flore.kernel.org%2Fr%2F94377f5c-d4f0-4c0f-
b0f6-5bf1cd7305b1%40linux.ibm.com%2F&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7Cb376c59325bf40bc08ce08de211479f4%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638984569012910679%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=1twO%2Ffle%2BX3EKlku7P9C8ZlQQUB2B9r%2FvF8ZaQdVz8k%3D&reserved=0
Signed-off-by: David Hildenbrand (Red Hat) <[email protected]>
---
arch/powerpc/Kconfig | 1 +
include/linux/mm.h | 12 +++++++++---
mm/Kconfig | 7 +++++++
3 files changed, 17 insertions(+), 3 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/include/linux/mm.h b/include/linux/mm.h
index d16b33bacc32b..2646ba7c96a49 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 +2087,16 @@ 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: with hugetlb, we expect no folios larger than 16
GiB.
+ */
+#define MAX_FOLIO_ORDER (16 * GIGA / PAGE_SIZE)
