[PATCH v3 00/10] mm: thp: always enable mTHP support

[PATCH v3 00/10] mm: thp: always enable mTHP support

[Luiz Capitulino]

Today, if an architecture implements has_transparent_hugepage() and the CPU
lacks support for PMD-sized pages, the THP code disables all THP, including
mTHP. In addition, the kernel lacks a well defined API to check for
PMD-sized page support. It currently relies on has_transparent_hugepage()
and thp_disabled_by_hw(), but they are not well defined and are tied to
THP support.

This series addresses both issues by introducing a new well defined API
to query PMD-sized page support: pgtable_has_pmd_leaves(). Using this
new helper, we ensure that mTHP remains enabled even when the
architecture or CPU doesn't support PMD-sized pages.

Thanks to David Hildenbrand for suggesting this improvement and for
providing guidance (all bugs and misconceptions are mine).

This applies to Linus tree bfe62a454542 ("Merge tag 'soc-fixes-7.0-2'
of git://git.kernel.org/pub/scm/linux/kernel/git/soc/soc").

v3
--

- Rebased on top of latest Linus tree
- Removed i915 patch as driver dropped has_transparent_hugepage() usage
- Moved init_arch_has_pmd_leaves() call in start_kernel() to avoid conflict
  with early_param handlers clearing CPU feature flags
- Fixed build error with CONFIG_MMU=n (kernel test robot)
- Fixed huge_anon_orders_inherit default setting when !pgtable_pmd_leaves() (Baolin)
- Small commit changelog improvements

v2
--
- Added support for always enabling mTHPs for shmem (Baolin)
- Improved commits changelog & added reviewed-by

v1
--
- Call init_arch_has_pmd_leaves() from start_kernel()
- Keep pgtable_has_pmd_leaves() calls tied to CONFIG_TRANSPARENT_HUGEPAGE (David)
- Clear PUD_ORDER when clearing PMD_ORDER (David)
- Small changelog improvements (David)
- Rebased on top of latest mm-new

Luiz Capitulino (10):
  docs: tmpfs: remove implementation detail reference
  mm: introduce pgtable_has_pmd_leaves()
  drivers: dax: use pgtable_has_pmd_leaves()
  drivers: nvdimm: use pgtable_has_pmd_leaves()
  mm: debug_vm_pgtable: use pgtable_has_pmd_leaves()
  mm: shmem: drop has_transparent_hugepage() usage
  treewide: rename has_transparent_hugepage() to arch_has_pmd_leaves()
  mm: replace thp_disabled_by_hw() with pgtable_has_pmd_leaves()
  mm: thp: always enable mTHP support
  mm: thp: x86: cleanup PSE feature bit usage

 Documentation/filesystems/tmpfs.rst           |  5 ++---
 arch/mips/include/asm/pgtable.h               |  4 ++--
 arch/mips/mm/tlb-r4k.c                        |  4 ++--
 arch/powerpc/include/asm/book3s/64/hash-4k.h  |  2 +-
 arch/powerpc/include/asm/book3s/64/hash-64k.h |  2 +-
 arch/powerpc/include/asm/book3s/64/pgtable.h  | 10 +++++-----
 arch/powerpc/include/asm/book3s/64/radix.h    |  2 +-
 arch/powerpc/mm/book3s64/hash_pgtable.c       |  4 ++--
 arch/s390/include/asm/pgtable.h               |  4 ++--
 arch/x86/include/asm/pgtable.h                |  6 ------
 arch/x86/include/asm/pgtable_32.h             |  6 ++++++
 drivers/dax/dax-private.h                     |  2 +-
 drivers/nvdimm/pfn_devs.c                     |  6 ++++--
 include/linux/huge_mm.h                       |  7 -------
 include/linux/pgtable.h                       | 19 ++++++++++++++++--
 init/main.c                                   |  1 +
 mm/debug_vm_pgtable.c                         | 20 +++++++++----------
 mm/huge_memory.c                              | 15 +++++++-------
 mm/memory.c                                   | 10 +++++++++-
 mm/shmem.c                                    | 11 +++++-----
 20 files changed, 80 insertions(+), 60 deletions(-)

-- 
2.53.0

[PATCH v3 01/10] docs: tmpfs: remove implementation detail reference

[Luiz Capitulino]

The tmpfs.rst doc references the has_transparent_hugepage() helper, which
is an implementation detail in the kernel and not relevant for users
wishing to properly configure THP support for tmpfs. Remove it.

Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Luiz Capitulino <luizcap@redhat.com>
---
 Documentation/filesystems/tmpfs.rst | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/Documentation/filesystems/tmpfs.rst b/Documentation/filesystems/tmpfs.rst
index d677e0428c3f..46fc986c3388 100644
--- a/Documentation/filesystems/tmpfs.rst
+++ b/Documentation/filesystems/tmpfs.rst
@@ -109,9 +109,8 @@ noswap  Disables swap. Remounts must respect the original settings.
 ======  ===========================================================
 
 tmpfs also supports Transparent Huge Pages which requires a kernel
-configured with CONFIG_TRANSPARENT_HUGEPAGE and with huge supported for
-your system (has_transparent_hugepage(), which is architecture specific).
-The mount options for this are:
+configured with CONFIG_TRANSPARENT_HUGEPAGE and with huge pages
+supported for your system. The mount options for this are:
 
 ================ ==============================================================
 huge=never       Do not allocate huge pages.  This is the default.
-- 
2.53.0

[PATCH v3 02/10] mm: introduce pgtable_has_pmd_leaves()

[Luiz Capitulino]

Currently, we have two helpers that check for PMD-sized pages but have
different names and slightly different semantics:

- has_transparent_hugepage(): the name suggests it checks if THP is
  enabled, but when CONFIG_TRANSPARENT_HUGEPAGE=y and the architecture
  implements this helper, it actually checks if the CPU supports
  PMD-sized pages

- thp_disabled_by_hw(): the name suggests it checks if THP is disabled
  by the hardware, but it just returns a cached value acquired with
  has_transparent_hugepage(). This helper is used in fast paths

This commit introduces a new helper called pgtable_has_pmd_leaves()
which is intended to replace both has_transparent_hugepage() and
thp_disabled_by_hw(). pgtable_has_pmd_leaves() has very clear semantics:
it returns true if the CPU supports PMD-sized pages and false otherwise.
It always returns a cached value, so it can be used in fast paths.

The new helper requires an initialization step which is performed by
init_arch_has_pmd_leaves(). We call init_arch_has_pmd_leaves() early
during boot in start_kernel() right after parse_early_param() but before
parse_args(). This allows early_param() handlers to change CPU flags if
needed (eg. parse_memopt() in x86-32) while also allowing users to use
the API from __setup() handlers.

The next commits will convert users of both has_transparent_hugepage()
and thp_disabled_by_hw() to pgtable_has_pmd_leaves().

Signed-off-by: Luiz Capitulino <luizcap@redhat.com>
---
 include/linux/pgtable.h | 15 +++++++++++++++
 init/main.c             |  1 +
 mm/memory.c             |  8 ++++++++
 3 files changed, 24 insertions(+)

diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index a50df42a893f..c4c5282f795c 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -2192,6 +2192,21 @@ static inline const char *pgtable_level_to_str(enum pgtable_level level)
 	}
 }
 
+#ifdef CONFIG_MMU
+extern bool __arch_has_pmd_leaves;
+static inline bool pgtable_has_pmd_leaves(void)
+{
+	return __arch_has_pmd_leaves;
+}
+void __init init_arch_has_pmd_leaves(void);
+#else
+static inline bool pgtable_has_pmd_leaves(void)
+{
+	return false;
+}
+static inline void __init init_arch_has_pmd_leaves(void) { }
+#endif
+
 #endif /* !__ASSEMBLY__ */
 
 #if !defined(MAX_POSSIBLE_PHYSMEM_BITS) && !defined(CONFIG_64BIT)
diff --git a/init/main.c b/init/main.c
index 1cb395dd94e4..07f2ddbf9677 100644
--- a/init/main.c
+++ b/init/main.c
@@ -1044,6 +1044,7 @@ void start_kernel(void)
 	print_kernel_cmdline(saved_command_line);
 	/* parameters may set static keys */
 	parse_early_param();
+	init_arch_has_pmd_leaves();
 	after_dashes = parse_args("Booting kernel",
 				  static_command_line, __start___param,
 				  __stop___param - __start___param,
diff --git a/mm/memory.c b/mm/memory.c
index c65e82c86fed..5ee312c30f2d 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -177,6 +177,14 @@ static int __init init_zero_pfn(void)
 }
 early_initcall(init_zero_pfn);
 
+bool __arch_has_pmd_leaves __read_mostly;
+EXPORT_SYMBOL(__arch_has_pmd_leaves);
+
+void __init init_arch_has_pmd_leaves(void)
+{
+	__arch_has_pmd_leaves = has_transparent_hugepage();
+}
+
 void mm_trace_rss_stat(struct mm_struct *mm, int member)
 {
 	trace_rss_stat(mm, member);
-- 
2.53.0

[PATCH v3 03/10] drivers: dax: use pgtable_has_pmd_leaves()

[Luiz Capitulino]

dax_align_valid() uses has_transparent_hugepage() to check if PMD-sized
pages are supported, use pgtable_has_pmd_leaves() instead.

Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
Signed-off-by: Luiz Capitulino <luizcap@redhat.com>
---
 drivers/dax/dax-private.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/dax/dax-private.h b/drivers/dax/dax-private.h
index c6ae27c982f4..97b577f4107b 100644
--- a/drivers/dax/dax-private.h
+++ b/drivers/dax/dax-private.h
@@ -119,7 +119,7 @@ static inline bool dax_align_valid(unsigned long align)
 {
 	if (align == PUD_SIZE && IS_ENABLED(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD))
 		return true;
-	if (align == PMD_SIZE && has_transparent_hugepage())
+	if (align == PMD_SIZE && pgtable_has_pmd_leaves())
 		return true;
 	if (align == PAGE_SIZE)
 		return true;
-- 
2.53.0

[PATCH v3 04/10] drivers: nvdimm: use pgtable_has_pmd_leaves()

[Luiz Capitulino]

nd_pfn_supported_alignments() and nd_pfn_default_alignment() use
has_transparent_hugepage() to check if THP is supported with PMD-sized
pages. Use pgtable_has_pmd_leaves() instead. Also, check for
IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) to preserve the current
implementation semantics.

Signed-off-by: Luiz Capitulino <luizcap@redhat.com>
---
 drivers/nvdimm/pfn_devs.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/nvdimm/pfn_devs.c b/drivers/nvdimm/pfn_devs.c
index 8fa9c16aba7e..457eb54e7ab6 100644
--- a/drivers/nvdimm/pfn_devs.c
+++ b/drivers/nvdimm/pfn_devs.c
@@ -94,7 +94,8 @@ static unsigned long *nd_pfn_supported_alignments(unsigned long *alignments)
 
 	alignments[0] = PAGE_SIZE;
 
-	if (has_transparent_hugepage()) {
+	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
+	    pgtable_has_pmd_leaves()) {
 		alignments[1] = HPAGE_PMD_SIZE;
 		if (has_transparent_pud_hugepage())
 			alignments[2] = HPAGE_PUD_SIZE;
@@ -109,7 +110,8 @@ static unsigned long *nd_pfn_supported_alignments(unsigned long *alignments)
 static unsigned long nd_pfn_default_alignment(void)
 {
 
-	if (has_transparent_hugepage())
+	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
+	    pgtable_has_pmd_leaves())
 		return HPAGE_PMD_SIZE;
 	return PAGE_SIZE;
 }
-- 
2.53.0

[PATCH v3 05/10] mm: debug_vm_pgtable: use pgtable_has_pmd_leaves()

[Luiz Capitulino]

debug_vm_pgtable calls has_transparent_hugepage() in multiple places to
check if PMD-sized pages are supported, use pgtable_has_pmd_leaves()
instead.

Signed-off-by: Luiz Capitulino <luizcap@redhat.com>
---
 mm/debug_vm_pgtable.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index 83cf07269f13..b3e30baaeceb 100644
--- a/mm/debug_vm_pgtable.c
+++ b/mm/debug_vm_pgtable.c
@@ -177,7 +177,7 @@ static void __init pmd_basic_tests(struct pgtable_debug_args *args, int idx)
 	unsigned long val = idx, *ptr = &val;
 	pmd_t pmd;
 
-	if (!has_transparent_hugepage())
+	if (!pgtable_has_pmd_leaves())
 		return;
 
 	pr_debug("Validating PMD basic (%pGv)\n", ptr);
@@ -222,7 +222,7 @@ static void __init pmd_advanced_tests(struct pgtable_debug_args *args)
 	pmd_t pmd;
 	unsigned long vaddr = args->vaddr;
 
-	if (!has_transparent_hugepage())
+	if (!pgtable_has_pmd_leaves())
 		return;
 
 	page = (args->pmd_pfn != ULONG_MAX) ? pfn_to_page(args->pmd_pfn) : NULL;
@@ -283,7 +283,7 @@ static void __init pmd_leaf_tests(struct pgtable_debug_args *args)
 {
 	pmd_t pmd;
 
-	if (!has_transparent_hugepage())
+	if (!pgtable_has_pmd_leaves())
 		return;
 
 	pr_debug("Validating PMD leaf\n");
@@ -688,7 +688,7 @@ static void __init pmd_protnone_tests(struct pgtable_debug_args *args)
 	if (!IS_ENABLED(CONFIG_NUMA_BALANCING))
 		return;
 
-	if (!has_transparent_hugepage())
+	if (!pgtable_has_pmd_leaves())
 		return;
 
 	pr_debug("Validating PMD protnone\n");
@@ -737,7 +737,7 @@ static void __init pmd_soft_dirty_tests(struct pgtable_debug_args *args)
 	if (!pgtable_supports_soft_dirty())
 		return;
 
-	if (!has_transparent_hugepage())
+	if (!pgtable_has_pmd_leaves())
 		return;
 
 	pr_debug("Validating PMD soft dirty\n");
@@ -754,7 +754,7 @@ static void __init pmd_leaf_soft_dirty_tests(struct pgtable_debug_args *args)
 	    !IS_ENABLED(CONFIG_ARCH_ENABLE_THP_MIGRATION))
 		return;
 
-	if (!has_transparent_hugepage())
+	if (!pgtable_has_pmd_leaves())
 		return;
 
 	pr_debug("Validating PMD swap soft dirty\n");
@@ -825,7 +825,7 @@ static void __init pmd_softleaf_tests(struct pgtable_debug_args *args)
 	swp_entry_t arch_entry;
 	pmd_t pmd1, pmd2;
 
-	if (!has_transparent_hugepage())
+	if (!pgtable_has_pmd_leaves())
 		return;
 
 	pr_debug("Validating PMD swap\n");
@@ -906,7 +906,7 @@ static void __init pmd_thp_tests(struct pgtable_debug_args *args)
 {
 	pmd_t pmd;
 
-	if (!has_transparent_hugepage())
+	if (!pgtable_has_pmd_leaves())
 		return;
 
 	pr_debug("Validating PMD based THP\n");
@@ -997,7 +997,7 @@ static void __init destroy_args(struct pgtable_debug_args *args)
 	}
 
 	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
-	    has_transparent_hugepage() &&
+	    pgtable_has_pmd_leaves() &&
 	    args->pmd_pfn != ULONG_MAX) {
 		debug_vm_pgtable_free_huge_page(args, args->pmd_pfn, HPAGE_PMD_ORDER);
 		args->pmd_pfn = ULONG_MAX;
@@ -1249,7 +1249,7 @@ static int __init init_args(struct pgtable_debug_args *args)
 	}
 
 	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
-	    has_transparent_hugepage()) {
+	    pgtable_has_pmd_leaves()) {
 		page = debug_vm_pgtable_alloc_huge_page(args, HPAGE_PMD_ORDER);
 		if (page) {
 			args->pmd_pfn = page_to_pfn(page);
-- 
2.53.0

[PATCH v3 06/10] mm: shmem: drop has_transparent_hugepage() usage

[Luiz Capitulino]

Shmem uses has_transparent_hugepage() in the following ways:

- shmem_parse_one() and shmem_parse_huge(): Check if THP is built-in and
  if the CPU supports PMD-sized pages

- shmem_init(): Since the CONFIG_TRANSPARENT_HUGEPAGE guard is outside
  the code block calling has_transparent_hugepage(), the
  has_transparent_hugepage() call is exclusively checking if the CPU
  supports PMD-sized pages

While it's necessary to check if CONFIG_TRANSPARENT_HUGEPAGE is enabled
in all cases, shmem can determine mTHP size support at folio allocation
time. Therefore, drop has_transparent_hugepage() usage while keeping the
CONFIG_TRANSPARENT_HUGEPAGE checks.

Signed-off-by: Luiz Capitulino <luizcap@redhat.com>
---
 mm/shmem.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index b40f3cd48961..6f8b20d77e07 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -689,7 +689,7 @@ static int shmem_parse_huge(const char *str)
 	else
 		return -EINVAL;
 
-	if (!has_transparent_hugepage() &&
+	if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
 	    huge != SHMEM_HUGE_NEVER && huge != SHMEM_HUGE_DENY)
 		return -EINVAL;
 
@@ -4664,8 +4664,7 @@ static int shmem_parse_one(struct fs_context *fc, struct fs_parameter *param)
 	case Opt_huge:
 		ctx->huge = result.uint_32;
 		if (ctx->huge != SHMEM_HUGE_NEVER &&
-		    !(IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
-		      has_transparent_hugepage()))
+		    !IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
 			goto unsupported_parameter;
 		ctx->seen |= SHMEM_SEEN_HUGE;
 		break;
@@ -5451,7 +5450,7 @@ void __init shmem_init(void)
 #endif
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	if (has_transparent_hugepage() && shmem_huge > SHMEM_HUGE_DENY)
+	if (shmem_huge > SHMEM_HUGE_DENY)
 		SHMEM_SB(shm_mnt->mnt_sb)->huge = shmem_huge;
 	else
 		shmem_huge = SHMEM_HUGE_NEVER; /* just in case it was patched */
-- 
2.53.0

[PATCH v3 07/10] treewide: rename has_transparent_hugepage() to arch_has_pmd_leaves()

[Luiz Capitulino]

Now that all the has_transparent_hugepage() callers have been converted
to pgtable_has_pmd_leaves(), rename has_transparent_hugepage() to
arch_has_pmd_leaves() since that's what the helper checks for.

arch_has_pmd_leaves() is supposed to be called only by
init_arch_has_pmd_leaves(). The remaining exception is hugepage_init()
which will be converted in a future commit.

Signed-off-by: Luiz Capitulino <luizcap@redhat.com>
---
 arch/mips/include/asm/pgtable.h               |  4 ++--
 arch/mips/mm/tlb-r4k.c                        |  4 ++--
 arch/powerpc/include/asm/book3s/64/hash-4k.h  |  2 +-
 arch/powerpc/include/asm/book3s/64/hash-64k.h |  2 +-
 arch/powerpc/include/asm/book3s/64/pgtable.h  | 10 +++++-----
 arch/powerpc/include/asm/book3s/64/radix.h    |  2 +-
 arch/powerpc/mm/book3s64/hash_pgtable.c       |  4 ++--
 arch/s390/include/asm/pgtable.h               |  4 ++--
 arch/x86/include/asm/pgtable.h                |  4 ++--
 include/linux/pgtable.h                       |  4 ++--
 mm/huge_memory.c                              |  2 +-
 mm/memory.c                                   |  2 +-
 12 files changed, 22 insertions(+), 22 deletions(-)

diff --git a/arch/mips/include/asm/pgtable.h b/arch/mips/include/asm/pgtable.h
index fa7b935f947c..a97b788315e2 100644
--- a/arch/mips/include/asm/pgtable.h
+++ b/arch/mips/include/asm/pgtable.h
@@ -615,8 +615,8 @@ unsigned long io_remap_pfn_range_pfn(unsigned long pfn, unsigned long size);
 /* We don't have hardware dirty/accessed bits, generic_pmdp_establish is fine.*/
 #define pmdp_establish generic_pmdp_establish
 
-#define has_transparent_hugepage has_transparent_hugepage
-extern int has_transparent_hugepage(void);
+#define arch_has_pmd_leaves arch_has_pmd_leaves
+extern int arch_has_pmd_leaves(void);
 
 static inline int pmd_trans_huge(pmd_t pmd)
 {
diff --git a/arch/mips/mm/tlb-r4k.c b/arch/mips/mm/tlb-r4k.c
index 24fe85fa169d..c423b5784337 100644
--- a/arch/mips/mm/tlb-r4k.c
+++ b/arch/mips/mm/tlb-r4k.c
@@ -434,7 +434,7 @@ void add_wired_entry(unsigned long entrylo0, unsigned long entrylo1,
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 
-int has_transparent_hugepage(void)
+int arch_has_pmd_leaves(void)
 {
 	static unsigned int mask = -1;
 
@@ -450,7 +450,7 @@ int has_transparent_hugepage(void)
 	}
 	return mask == PM_HUGE_MASK;
 }
-EXPORT_SYMBOL(has_transparent_hugepage);
+EXPORT_SYMBOL(arch_has_pmd_leaves);
 
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE  */
 
diff --git a/arch/powerpc/include/asm/book3s/64/hash-4k.h b/arch/powerpc/include/asm/book3s/64/hash-4k.h
index 8e5bd9902bed..6744c2287199 100644
--- a/arch/powerpc/include/asm/book3s/64/hash-4k.h
+++ b/arch/powerpc/include/asm/book3s/64/hash-4k.h
@@ -165,7 +165,7 @@ extern void hash__pgtable_trans_huge_deposit(struct mm_struct *mm, pmd_t *pmdp,
 extern pgtable_t hash__pgtable_trans_huge_withdraw(struct mm_struct *mm, pmd_t *pmdp);
 extern pmd_t hash__pmdp_huge_get_and_clear(struct mm_struct *mm,
 				       unsigned long addr, pmd_t *pmdp);
-extern int hash__has_transparent_hugepage(void);
+extern int hash__arch_has_pmd_leaves(void);
 #endif
 
 #endif /* !__ASSEMBLER__ */
diff --git a/arch/powerpc/include/asm/book3s/64/hash-64k.h b/arch/powerpc/include/asm/book3s/64/hash-64k.h
index 7deb3a66890b..9392aba5e5dc 100644
--- a/arch/powerpc/include/asm/book3s/64/hash-64k.h
+++ b/arch/powerpc/include/asm/book3s/64/hash-64k.h
@@ -278,7 +278,7 @@ extern void hash__pgtable_trans_huge_deposit(struct mm_struct *mm, pmd_t *pmdp,
 extern pgtable_t hash__pgtable_trans_huge_withdraw(struct mm_struct *mm, pmd_t *pmdp);
 extern pmd_t hash__pmdp_huge_get_and_clear(struct mm_struct *mm,
 				       unsigned long addr, pmd_t *pmdp);
-extern int hash__has_transparent_hugepage(void);
+extern int hash__arch_has_pmd_leaves(void);
 #endif /*  CONFIG_TRANSPARENT_HUGEPAGE */
 
 #endif	/* __ASSEMBLER__ */
diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
index 1a91762b455d..e4d9b884af5c 100644
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
@@ -1121,14 +1121,14 @@ static inline void update_mmu_cache_pud(struct vm_area_struct *vma,
 {
 }
 
-extern int hash__has_transparent_hugepage(void);
-static inline int has_transparent_hugepage(void)
+extern int hash__arch_has_pmd_leaves(void);
+static inline int arch_has_pmd_leaves(void)
 {
 	if (radix_enabled())
-		return radix__has_transparent_hugepage();
-	return hash__has_transparent_hugepage();
+		return radix__arch_has_pmd_leaves();
+	return hash__arch_has_pmd_leaves();
 }
-#define has_transparent_hugepage has_transparent_hugepage
+#define arch_has_pmd_leaves arch_has_pmd_leaves
 
 static inline int has_transparent_pud_hugepage(void)
 {
diff --git a/arch/powerpc/include/asm/book3s/64/radix.h b/arch/powerpc/include/asm/book3s/64/radix.h
index da954e779744..c884a119cbd9 100644
--- a/arch/powerpc/include/asm/book3s/64/radix.h
+++ b/arch/powerpc/include/asm/book3s/64/radix.h
@@ -298,7 +298,7 @@ extern pmd_t radix__pmdp_huge_get_and_clear(struct mm_struct *mm,
 pud_t radix__pudp_huge_get_and_clear(struct mm_struct *mm,
 				     unsigned long addr, pud_t *pudp);
 
-static inline int radix__has_transparent_hugepage(void)
+static inline int radix__arch_has_pmd_leaves(void)
 {
 	/* For radix 2M at PMD level means thp */
 	if (mmu_psize_defs[MMU_PAGE_2M].shift == PMD_SHIFT)
diff --git a/arch/powerpc/mm/book3s64/hash_pgtable.c b/arch/powerpc/mm/book3s64/hash_pgtable.c
index ac2a24d15d2e..f7933c52cca9 100644
--- a/arch/powerpc/mm/book3s64/hash_pgtable.c
+++ b/arch/powerpc/mm/book3s64/hash_pgtable.c
@@ -370,7 +370,7 @@ pmd_t hash__pmdp_huge_get_and_clear(struct mm_struct *mm,
 	return old_pmd;
 }
 
-int hash__has_transparent_hugepage(void)
+int hash__arch_has_pmd_leaves(void)
 {
 
 	if (!mmu_has_feature(MMU_FTR_16M_PAGE))
@@ -399,7 +399,7 @@ int hash__has_transparent_hugepage(void)
 
 	return 1;
 }
-EXPORT_SYMBOL_GPL(hash__has_transparent_hugepage);
+EXPORT_SYMBOL_GPL(hash__arch_has_pmd_leaves);
 
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index 1c3c3be93be9..e638d914fbad 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -1776,8 +1776,8 @@ static inline int pmd_trans_huge(pmd_t pmd)
 	return pmd_leaf(pmd);
 }
 
-#define has_transparent_hugepage has_transparent_hugepage
-static inline int has_transparent_hugepage(void)
+#define arch_has_pmd_leaves arch_has_pmd_leaves
+static inline int arch_has_pmd_leaves(void)
 {
 	return cpu_has_edat1() ? 1 : 0;
 }
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 1662c5a8f445..8fe95270b713 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -314,8 +314,8 @@ static inline int pud_trans_huge(pud_t pud)
 }
 #endif
 
-#define has_transparent_hugepage has_transparent_hugepage
-static inline int has_transparent_hugepage(void)
+#define arch_has_pmd_leaves arch_has_pmd_leaves
+static inline int arch_has_pmd_leaves(void)
 {
 	return boot_cpu_has(X86_FEATURE_PSE);
 }
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index c4c5282f795c..4b52a3abeab5 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -2222,8 +2222,8 @@ static inline void __init init_arch_has_pmd_leaves(void) { }
 #endif
 #endif
 
-#ifndef has_transparent_hugepage
-#define has_transparent_hugepage() IS_BUILTIN(CONFIG_TRANSPARENT_HUGEPAGE)
+#ifndef arch_has_pmd_leaves
+#define arch_has_pmd_leaves() IS_BUILTIN(CONFIG_TRANSPARENT_HUGEPAGE)
 #endif
 
 #ifndef has_transparent_pud_hugepage
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index b298cba853ab..9e4889d1673f 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -908,7 +908,7 @@ static int __init hugepage_init(void)
 	int err;
 	struct kobject *hugepage_kobj;
 
-	if (!has_transparent_hugepage()) {
+	if (!arch_has_pmd_leaves()) {
 		transparent_hugepage_flags = 1 << TRANSPARENT_HUGEPAGE_UNSUPPORTED;
 		return -EINVAL;
 	}
diff --git a/mm/memory.c b/mm/memory.c
index 5ee312c30f2d..87a65f6eabfb 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -182,7 +182,7 @@ EXPORT_SYMBOL(__arch_has_pmd_leaves);
 
 void __init init_arch_has_pmd_leaves(void)
 {
-	__arch_has_pmd_leaves = has_transparent_hugepage();
+	__arch_has_pmd_leaves = arch_has_pmd_leaves();
 }
 
 void mm_trace_rss_stat(struct mm_struct *mm, int member)
-- 
2.53.0

[PATCH v3 08/10] mm: replace thp_disabled_by_hw() with pgtable_has_pmd_leaves()

[Luiz Capitulino]

Despite its name, thp_disabled_by_hw() just checks whether the
architecture supports PMD-sized pages. It returns true when
TRANSPARENT_HUGEPAGE_UNSUPPORTED is set in transparent_hugepage_flags,
this only occurs if the architecture implements arch_has_pmd_leaves()
and that function returns false.

Since pgtable_has_pmd_leaves() provides the same semantics, use it
instead.

Signed-off-by: Luiz Capitulino <luizcap@redhat.com>
---
 include/linux/huge_mm.h | 7 -------
 mm/huge_memory.c        | 6 ++----
 mm/memory.c             | 2 +-
 mm/shmem.c              | 2 +-
 4 files changed, 4 insertions(+), 13 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index a4d9f964dfde..e291a650b10f 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -47,7 +47,6 @@ vm_fault_t vmf_insert_folio_pud(struct vm_fault *vmf, struct folio *folio,
 				bool write);
 
 enum transparent_hugepage_flag {
-	TRANSPARENT_HUGEPAGE_UNSUPPORTED,
 	TRANSPARENT_HUGEPAGE_FLAG,
 	TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
 	TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG,
@@ -352,12 +351,6 @@ static inline bool vma_thp_disabled(struct vm_area_struct *vma,
 	return mm_flags_test(MMF_DISABLE_THP_EXCEPT_ADVISED, vma->vm_mm);
 }
 
-static inline bool thp_disabled_by_hw(void)
-{
-	/* If the hardware/firmware marked hugepage support disabled. */
-	return transparent_hugepage_flags & (1 << TRANSPARENT_HUGEPAGE_UNSUPPORTED);
-}
-
 unsigned long thp_get_unmapped_area(struct file *filp, unsigned long addr,
 		unsigned long len, unsigned long pgoff, unsigned long flags);
 unsigned long thp_get_unmapped_area_vmflags(struct file *filp, unsigned long addr,
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9e4889d1673f..86e489c0a150 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -125,7 +125,7 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma,
 	if (!vma->vm_mm)		/* vdso */
 		return 0;
 
-	if (thp_disabled_by_hw() || vma_thp_disabled(vma, vm_flags, forced_collapse))
+	if (!pgtable_has_pmd_leaves() || vma_thp_disabled(vma, vm_flags, forced_collapse))
 		return 0;
 
 	/* khugepaged doesn't collapse DAX vma, but page fault is fine. */
@@ -908,10 +908,8 @@ static int __init hugepage_init(void)
 	int err;
 	struct kobject *hugepage_kobj;
 
-	if (!arch_has_pmd_leaves()) {
-		transparent_hugepage_flags = 1 << TRANSPARENT_HUGEPAGE_UNSUPPORTED;
+	if (!pgtable_has_pmd_leaves())
 		return -EINVAL;
-	}
 
 	/*
 	 * hugepages can't be allocated by the buddy allocator
diff --git a/mm/memory.c b/mm/memory.c
index 87a65f6eabfb..29cb4ea33ba0 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5427,7 +5427,7 @@ vm_fault_t do_set_pmd(struct vm_fault *vmf, struct folio *folio, struct page *pa
 	 * PMD mappings if THPs are disabled. As we already have a THP,
 	 * behave as if we are forcing a collapse.
 	 */
-	if (thp_disabled_by_hw() || vma_thp_disabled(vma, vma->vm_flags,
+	if (!pgtable_has_pmd_leaves() || vma_thp_disabled(vma, vma->vm_flags,
 						     /* forced_collapse=*/ true))
 		return ret;
 
diff --git a/mm/shmem.c b/mm/shmem.c
index 6f8b20d77e07..613393eae5a9 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1839,7 +1839,7 @@ unsigned long shmem_allowable_huge_orders(struct inode *inode,
 	vm_flags_t vm_flags = vma ? vma->vm_flags : 0;
 	unsigned int global_orders;
 
-	if (thp_disabled_by_hw() || (vma && vma_thp_disabled(vma, vm_flags, shmem_huge_force)))
+	if (!pgtable_has_pmd_leaves() || (vma && vma_thp_disabled(vma, vm_flags, shmem_huge_force)))
 		return 0;
 
 	global_orders = shmem_huge_global_enabled(inode, index, write_end,
-- 
2.53.0

[PATCH v3 09/10] mm: thp: always enable mTHP support

[Luiz Capitulino]

If PMD-sized pages are not supported on an architecture (ie. the
arch implements arch_has_pmd_leaves() and it returns false) then the
current code disables all THP, including mTHP.

This commit fixes this by allowing mTHP to be always enabled for all
archs. When PMD-sized pages are not supported, its sysfs entry won't be
created and their mapping will be disallowed at page-fault time.

Similarly, this commit implements the following changes for shmem:

 - In shmem_allowable_huge_orders(): drop the pgtable_has_pmd_leaves()
   check so that mTHP sizes are considered
 - In shmem_alloc_and_add_folio(): don't consider PMD and PUD orders
   when PMD-sized pages are not supported by the CPU

Signed-off-by: Luiz Capitulino <luizcap@redhat.com>
---
 mm/huge_memory.c | 13 ++++++++-----
 mm/shmem.c       |  4 +++-
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 86e489c0a150..6de3d8ebc35c 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -118,6 +118,9 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma,
 	else
 		supported_orders = THP_ORDERS_ALL_FILE_DEFAULT;
 
+	if (!pgtable_has_pmd_leaves())
+		supported_orders &= ~(BIT(PMD_ORDER) | BIT(PUD_ORDER));
+
 	orders &= supported_orders;
 	if (!orders)
 		return 0;
@@ -125,7 +128,7 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma,
 	if (!vma->vm_mm)		/* vdso */
 		return 0;
 
-	if (!pgtable_has_pmd_leaves() || vma_thp_disabled(vma, vm_flags, forced_collapse))
+	if (vma_thp_disabled(vma, vm_flags, forced_collapse))
 		return 0;
 
 	/* khugepaged doesn't collapse DAX vma, but page fault is fine. */
@@ -787,7 +790,7 @@ static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
 	 * disable all other sizes. powerpc's PMD_ORDER isn't a compile-time
 	 * constant so we have to do this here.
 	 */
-	if (!anon_orders_configured)
+	if (!anon_orders_configured && pgtable_has_pmd_leaves())
 		huge_anon_orders_inherit = BIT(PMD_ORDER);
 
 	*hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
@@ -809,6 +812,9 @@ static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
 	}
 
 	orders = THP_ORDERS_ALL_ANON | THP_ORDERS_ALL_FILE_DEFAULT;
+	if (!pgtable_has_pmd_leaves())
+		orders &= ~(BIT(PMD_ORDER) | BIT(PUD_ORDER));
+
 	order = highest_order(orders);
 	while (orders) {
 		thpsize = thpsize_create(order, *hugepage_kobj);
@@ -908,9 +914,6 @@ static int __init hugepage_init(void)
 	int err;
 	struct kobject *hugepage_kobj;
 
-	if (!pgtable_has_pmd_leaves())
-		return -EINVAL;
-
 	/*
 	 * hugepages can't be allocated by the buddy allocator
 	 */
diff --git a/mm/shmem.c b/mm/shmem.c
index 613393eae5a9..b49a30475cb0 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1839,7 +1839,7 @@ unsigned long shmem_allowable_huge_orders(struct inode *inode,
 	vm_flags_t vm_flags = vma ? vma->vm_flags : 0;
 	unsigned int global_orders;
 
-	if (!pgtable_has_pmd_leaves() || (vma && vma_thp_disabled(vma, vm_flags, shmem_huge_force)))
+	if (vma && vma_thp_disabled(vma, vm_flags, shmem_huge_force))
 		return 0;
 
 	global_orders = shmem_huge_global_enabled(inode, index, write_end,
@@ -1947,6 +1947,8 @@ static struct folio *shmem_alloc_and_add_folio(struct vm_fault *vmf,
 
 	if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
 		orders = 0;
+	else if (!pgtable_has_pmd_leaves())
+		orders &= ~(BIT(PMD_ORDER) | BIT(PUD_ORDER));
 
 	if (orders > 0) {
 		suitable_orders = shmem_suitable_orders(inode, vmf,
-- 
2.53.0

[PATCH v3 10/10] mm: thp: x86: cleanup PSE feature bit usage

[Luiz Capitulino]

Historically, THP support on x86 checked the PSE feature bit to enable
THP. On 64-bit, this check is redundant since PSE is always enabled by
default for compatibility. On 32-bit, PSE can enable 2 MiB or 4 MiB
page sizes so it must be checked. To clean this up, this commit:

1. Drops arch_has_pmd_leaves() from common x86 code. For 64-bit,
   we assume PMD-sized pages are always supported

2. Checks for PSE only on 32-bit by implementing arch_has_pmd_leaves()

Signed-off-by: Luiz Capitulino <luizcap@redhat.com>
---
 arch/x86/include/asm/pgtable.h    | 6 ------
 arch/x86/include/asm/pgtable_32.h | 6 ++++++
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 8fe95270b713..f45568f9513c 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -314,12 +314,6 @@ static inline int pud_trans_huge(pud_t pud)
 }
 #endif
 
-#define arch_has_pmd_leaves arch_has_pmd_leaves
-static inline int arch_has_pmd_leaves(void)
-{
-	return boot_cpu_has(X86_FEATURE_PSE);
-}
-
 #ifdef CONFIG_ARCH_SUPPORTS_PMD_PFNMAP
 static inline bool pmd_special(pmd_t pmd)
 {
diff --git a/arch/x86/include/asm/pgtable_32.h b/arch/x86/include/asm/pgtable_32.h
index acea0cfa2460..1db3214cfb45 100644
--- a/arch/x86/include/asm/pgtable_32.h
+++ b/arch/x86/include/asm/pgtable_32.h
@@ -44,6 +44,12 @@ do {						\
 	flush_tlb_one_kernel((vaddr));		\
 } while (0)
 
+#define arch_has_pmd_leaves arch_has_pmd_leaves
+static inline int arch_has_pmd_leaves(void)
+{
+	return boot_cpu_has(X86_FEATURE_PSE);
+}
+
 #endif /* !__ASSEMBLER__ */
 
 /*
-- 
2.53.0

Re: [PATCH v3 00/10] mm: thp: always enable mTHP support

[Lance Yang]

+Cc THP

Some folks seem to be missing from CC for this series. Please run
scripts/get_maintainer.pl; it's your friend :)

Thanks,
Lance

On Wed, Apr 08, 2026 at 04:22:55PM -0400, Luiz Capitulino wrote:
>Today, if an architecture implements has_transparent_hugepage() and the CPU
>lacks support for PMD-sized pages, the THP code disables all THP, including
>mTHP. In addition, the kernel lacks a well defined API to check for
>PMD-sized page support. It currently relies on has_transparent_hugepage()
>and thp_disabled_by_hw(), but they are not well defined and are tied to
>THP support.
>
>This series addresses both issues by introducing a new well defined API
>to query PMD-sized page support: pgtable_has_pmd_leaves(). Using this
>new helper, we ensure that mTHP remains enabled even when the
>architecture or CPU doesn't support PMD-sized pages.
>
>Thanks to David Hildenbrand for suggesting this improvement and for
>providing guidance (all bugs and misconceptions are mine).
>
>This applies to Linus tree bfe62a454542 ("Merge tag 'soc-fixes-7.0-2'
>of git://git.kernel.org/pub/scm/linux/kernel/git/soc/soc").
>
>v3
>--
>
>- Rebased on top of latest Linus tree
>- Removed i915 patch as driver dropped has_transparent_hugepage() usage
>- Moved init_arch_has_pmd_leaves() call in start_kernel() to avoid conflict
>  with early_param handlers clearing CPU feature flags
>- Fixed build error with CONFIG_MMU=n (kernel test robot)
>- Fixed huge_anon_orders_inherit default setting when !pgtable_pmd_leaves() (Baolin)
>- Small commit changelog improvements
>
>v2
>--
>- Added support for always enabling mTHPs for shmem (Baolin)
>- Improved commits changelog & added reviewed-by
>
>v1
>--
>- Call init_arch_has_pmd_leaves() from start_kernel()
>- Keep pgtable_has_pmd_leaves() calls tied to CONFIG_TRANSPARENT_HUGEPAGE (David)
>- Clear PUD_ORDER when clearing PMD_ORDER (David)
>- Small changelog improvements (David)
>- Rebased on top of latest mm-new
>
>Luiz Capitulino (10):
>  docs: tmpfs: remove implementation detail reference
>  mm: introduce pgtable_has_pmd_leaves()
>  drivers: dax: use pgtable_has_pmd_leaves()
>  drivers: nvdimm: use pgtable_has_pmd_leaves()
>  mm: debug_vm_pgtable: use pgtable_has_pmd_leaves()
>  mm: shmem: drop has_transparent_hugepage() usage
>  treewide: rename has_transparent_hugepage() to arch_has_pmd_leaves()
>  mm: replace thp_disabled_by_hw() with pgtable_has_pmd_leaves()
>  mm: thp: always enable mTHP support
>  mm: thp: x86: cleanup PSE feature bit usage
>
> Documentation/filesystems/tmpfs.rst           |  5 ++---
> arch/mips/include/asm/pgtable.h               |  4 ++--
> arch/mips/mm/tlb-r4k.c                        |  4 ++--
> arch/powerpc/include/asm/book3s/64/hash-4k.h  |  2 +-
> arch/powerpc/include/asm/book3s/64/hash-64k.h |  2 +-
> arch/powerpc/include/asm/book3s/64/pgtable.h  | 10 +++++-----
> arch/powerpc/include/asm/book3s/64/radix.h    |  2 +-
> arch/powerpc/mm/book3s64/hash_pgtable.c       |  4 ++--
> arch/s390/include/asm/pgtable.h               |  4 ++--
> arch/x86/include/asm/pgtable.h                |  6 ------
> arch/x86/include/asm/pgtable_32.h             |  6 ++++++
> drivers/dax/dax-private.h                     |  2 +-
> drivers/nvdimm/pfn_devs.c                     |  6 ++++--
> include/linux/huge_mm.h                       |  7 -------
> include/linux/pgtable.h                       | 19 ++++++++++++++++--
> init/main.c                                   |  1 +
> mm/debug_vm_pgtable.c                         | 20 +++++++++----------
> mm/huge_memory.c                              | 15 +++++++-------
> mm/memory.c                                   | 10 +++++++++-
> mm/shmem.c                                    | 11 +++++-----
> 20 files changed, 80 insertions(+), 60 deletions(-)
>
>-- 
>2.53.0
>
>

Re: [PATCH v3 00/10] mm: thp: always enable mTHP support

[Lorenzo Stoakes]

On Thu, Apr 09, 2026 at 04:29:36PM +0800, Lance Yang wrote:
> +Cc THP
>
> Some folks seem to be missing from CC for this series. Please run
> scripts/get_maintainer.pl; it's your friend :)

Please also use ljs@kernel.org for me, I'm now ignoring mails that are sent to
my old address, so you won't get replies if you send it to the wrong one :)

(My upstream bandwidth is dramatically reduced and I can't justify checking both
places.)

I will try to take a look at this when I get time, but really this is something
to queue up for next cycle clearly at this point!

I really do appreciate work that pays down technical debt however, so just to
be clear, I'm glad you're doing that :>)

Cheers, Lorenzo