[PATCH v3 0/7] enable PT_RECLAIM on all 64-bit architectures

[PATCH v3 0/7] enable PT_RECLAIM on all 64-bit architectures

[Qi Zheng]

From: Qi Zheng <zhengqi.arch@bytedance.com>

Changes in v3:
 - modify the commit message in [PATCH v3 1/7] (suggested by David Hildenbrand)
 - make PT_RECLAIM depends on MMU_GATHER_RCU_TABLE_FREE instead of 64BIT
 - collect Acked-by
 - rebase onto the next-20251217

Changelog in v2:
 - fix compilation errors (reported by Magnus Lindholm and kernel test robot)
 - adjust some code style (suggested by Huacai Chen)
 - make PT_RECLAIM user-unselectable (suggested by David Hildenbrand)
 - rebase onto the next-20251119

Hi all,

This series aims to enable PT_RECLAIM on all 64-bit architectures.

On a 64-bit system, madvise(MADV_DONTNEED) may cause a large number of empty PTE
page table pages (such as 100GB+). To resolve this problem, we need to enable
PT_RECLAIM, which depends on MMU_GATHER_RCU_TABLE_FREE.

Therefore, this series first enables MMU_GATHER_RCU_TABLE_FREE on all 64-bit
architectures, and finally makes PT_RECLAIM depend on MMU_GATHER_RCU_TABLE_FREE.
This way, PT_RECLAIM can be enabled by default on all 64-bit architectures.

Of course, this will also be enabled on some 32-bit architectures that already
support MMU_GATHER_RCU_TABLE_FREE. That's fine, PT_RECLAIM works well on all
32-bit architectures as well. Although the benefit isn't significant, there's
still memory that can be reclaimed. Perhaps PT_RECLAIM can be enabled on all
32-bit architectures in the future.

Comments and suggestions are welcome!

Thanks,
Qi

Qi Zheng (7):
  mm: change mm/pt_reclaim.c to use asm/tlb.h instead of
    asm-generic/tlb.h
  alpha: mm: enable MMU_GATHER_RCU_TABLE_FREE
  LoongArch: mm: enable MMU_GATHER_RCU_TABLE_FREE
  mips: mm: enable MMU_GATHER_RCU_TABLE_FREE
  parisc: mm: enable MMU_GATHER_RCU_TABLE_FREE
  um: mm: enable MMU_GATHER_RCU_TABLE_FREE
  mm: make PT_RECLAIM depends on MMU_GATHER_RCU_TABLE_FREE

 arch/alpha/Kconfig                   | 1 +
 arch/alpha/include/asm/tlb.h         | 6 +++---
 arch/loongarch/Kconfig               | 1 +
 arch/loongarch/include/asm/pgalloc.h | 7 +++----
 arch/mips/Kconfig                    | 1 +
 arch/mips/include/asm/pgalloc.h      | 7 +++----
 arch/parisc/Kconfig                  | 1 +
 arch/parisc/include/asm/tlb.h        | 4 ++--
 arch/um/Kconfig                      | 1 +
 arch/x86/Kconfig                     | 1 -
 mm/Kconfig                           | 9 ++-------
 mm/pt_reclaim.c                      | 2 +-
 12 files changed, 19 insertions(+), 22 deletions(-)

-- 
2.20.1

[PATCH v3 1/7] mm: change mm/pt_reclaim.c to use asm/tlb.h instead of asm-generic/tlb.h

[Qi Zheng]

From: Qi Zheng <zhengqi.arch@bytedance.com>

Generally, the asm/tlb.h will include asm-generic/tlb.h, so change
mm/pt_reclaim.c to use asm/tlb.h instead of asm-generic/tlb.h. This is a
preparation for enabling CONFIG_PT_RECLAIM on other architectures, such as
alpha.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
---
 mm/pt_reclaim.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/pt_reclaim.c b/mm/pt_reclaim.c
index 0d9cfbf4fe5d8..46771cfff8239 100644
--- a/mm/pt_reclaim.c
+++ b/mm/pt_reclaim.c
@@ -2,7 +2,7 @@
 #include <linux/hugetlb.h>
 #include <linux/pgalloc.h>
 
-#include <asm-generic/tlb.h>
+#include <asm/tlb.h>
 
 #include "internal.h"
 
-- 
2.20.1

[PATCH v3 2/7] alpha: mm: enable MMU_GATHER_RCU_TABLE_FREE

[Qi Zheng]

From: Qi Zheng <zhengqi.arch@bytedance.com>

On a 64-bit system, madvise(MADV_DONTNEED) may cause a large number of
empty PTE page table pages (such as 100GB+). To resolve this problem,
first enable MMU_GATHER_RCU_TABLE_FREE to prepare for enabling the
PT_RECLAIM feature, which resolves this problem.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Matt Turner <mattst88@gmail.com>
---
 arch/alpha/Kconfig           | 1 +
 arch/alpha/include/asm/tlb.h | 6 +++---
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/alpha/Kconfig b/arch/alpha/Kconfig
index 80367f2cf821c..6c7dbf0adad62 100644
--- a/arch/alpha/Kconfig
+++ b/arch/alpha/Kconfig
@@ -38,6 +38,7 @@ config ALPHA
 	select OLD_SIGSUSPEND
 	select CPU_NO_EFFICIENT_FFS if !ALPHA_EV67
 	select MMU_GATHER_NO_RANGE
+	select MMU_GATHER_RCU_TABLE_FREE
 	select SPARSEMEM_EXTREME if SPARSEMEM
 	select ZONE_DMA
 	help
diff --git a/arch/alpha/include/asm/tlb.h b/arch/alpha/include/asm/tlb.h
index 4f79e331af5ea..ad586b898fd6b 100644
--- a/arch/alpha/include/asm/tlb.h
+++ b/arch/alpha/include/asm/tlb.h
@@ -4,7 +4,7 @@
 
 #include <asm-generic/tlb.h>
 
-#define __pte_free_tlb(tlb, pte, address)		pte_free((tlb)->mm, pte)
-#define __pmd_free_tlb(tlb, pmd, address)		pmd_free((tlb)->mm, pmd)
- 
+#define __pte_free_tlb(tlb, pte, address)	tlb_remove_ptdesc((tlb), page_ptdesc(pte))
+#define __pmd_free_tlb(tlb, pmd, address)	tlb_remove_ptdesc((tlb), virt_to_ptdesc(pmd))
+
 #endif
-- 
2.20.1

[PATCH v3 3/7] LoongArch: mm: enable MMU_GATHER_RCU_TABLE_FREE

[Qi Zheng]

From: Qi Zheng <zhengqi.arch@bytedance.com>

On a 64-bit system, madvise(MADV_DONTNEED) may cause a large number of
empty PTE page table pages (such as 100GB+). To resolve this problem,
first enable MMU_GATHER_RCU_TABLE_FREE to prepare for enabling the
PT_RECLAIM feature, which resolves this problem.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: WANG Xuerui <kernel@xen0n.name>
---
 arch/loongarch/Kconfig               | 1 +
 arch/loongarch/include/asm/pgalloc.h | 7 +++----
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index 730f342145197..43d5b863e1fb2 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -187,6 +187,7 @@ config LOONGARCH
 	select IRQ_LOONGARCH_CPU
 	select LOCK_MM_AND_FIND_VMA
 	select MMU_GATHER_MERGE_VMAS if MMU
+	select MMU_GATHER_RCU_TABLE_FREE
 	select MODULES_USE_ELF_RELA if MODULES
 	select NEED_PER_CPU_EMBED_FIRST_CHUNK
 	select NEED_PER_CPU_PAGE_FIRST_CHUNK
diff --git a/arch/loongarch/include/asm/pgalloc.h b/arch/loongarch/include/asm/pgalloc.h
index 08dcc698ec184..248f62d0b590e 100644
--- a/arch/loongarch/include/asm/pgalloc.h
+++ b/arch/loongarch/include/asm/pgalloc.h
@@ -55,8 +55,7 @@ static inline pte_t *pte_alloc_one_kernel(struct mm_struct *mm)
 	return pte;
 }
 
-#define __pte_free_tlb(tlb, pte, address)	\
-	tlb_remove_ptdesc((tlb), page_ptdesc(pte))
+#define __pte_free_tlb(tlb, pte, address)	tlb_remove_ptdesc((tlb), page_ptdesc(pte))
 
 #ifndef __PAGETABLE_PMD_FOLDED
 
@@ -79,7 +78,7 @@ static inline pmd_t *pmd_alloc_one(struct mm_struct *mm, unsigned long address)
 	return pmd;
 }
 
-#define __pmd_free_tlb(tlb, x, addr)	pmd_free((tlb)->mm, x)
+#define __pmd_free_tlb(tlb, x, addr)	tlb_remove_ptdesc((tlb), virt_to_ptdesc(x))
 
 #endif
 
@@ -99,7 +98,7 @@ static inline pud_t *pud_alloc_one(struct mm_struct *mm, unsigned long address)
 	return pud;
 }
 
-#define __pud_free_tlb(tlb, x, addr)	pud_free((tlb)->mm, x)
+#define __pud_free_tlb(tlb, x, addr)	tlb_remove_ptdesc((tlb), virt_to_ptdesc(x))
 
 #endif /* __PAGETABLE_PUD_FOLDED */
 
-- 
2.20.1

[PATCH v3 4/7] mips: mm: enable MMU_GATHER_RCU_TABLE_FREE

[Qi Zheng]

From: Qi Zheng <zhengqi.arch@bytedance.com>

On a 64-bit system, madvise(MADV_DONTNEED) may cause a large number of
empty PTE page table pages (such as 100GB+). To resolve this problem,
first enable MMU_GATHER_RCU_TABLE_FREE to prepare for enabling the
PT_RECLAIM feature, which resolves this problem.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
---
 arch/mips/Kconfig               | 1 +
 arch/mips/include/asm/pgalloc.h | 7 +++----
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index b88b97139fa8e..c0c94e26ce396 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -99,6 +99,7 @@ config MIPS
 	select IRQ_FORCED_THREADING
 	select ISA if EISA
 	select LOCK_MM_AND_FIND_VMA
+	select MMU_GATHER_RCU_TABLE_FREE
 	select MODULES_USE_ELF_REL if MODULES
 	select MODULES_USE_ELF_RELA if MODULES && 64BIT
 	select PERF_USE_VMALLOC
diff --git a/arch/mips/include/asm/pgalloc.h b/arch/mips/include/asm/pgalloc.h
index 7a04381efa0b5..895bf79e76762 100644
--- a/arch/mips/include/asm/pgalloc.h
+++ b/arch/mips/include/asm/pgalloc.h
@@ -48,8 +48,7 @@ static inline void pud_populate(struct mm_struct *mm, pud_t *pud, pmd_t *pmd)
 extern void pgd_init(void *addr);
 extern pgd_t *pgd_alloc(struct mm_struct *mm);
 
-#define __pte_free_tlb(tlb, pte, address)	\
-	tlb_remove_ptdesc((tlb), page_ptdesc(pte))
+#define __pte_free_tlb(tlb, pte, address)	tlb_remove_ptdesc((tlb), page_ptdesc(pte))
 
 #ifndef __PAGETABLE_PMD_FOLDED
 
@@ -72,7 +71,7 @@ static inline pmd_t *pmd_alloc_one(struct mm_struct *mm, unsigned long address)
 	return pmd;
 }
 
-#define __pmd_free_tlb(tlb, x, addr)	pmd_free((tlb)->mm, x)
+#define __pmd_free_tlb(tlb, x, addr)	tlb_remove_ptdesc((tlb), virt_to_ptdesc(x))
 
 #endif
 
@@ -97,7 +96,7 @@ static inline void p4d_populate(struct mm_struct *mm, p4d_t *p4d, pud_t *pud)
 	set_p4d(p4d, __p4d((unsigned long)pud));
 }
 
-#define __pud_free_tlb(tlb, x, addr)	pud_free((tlb)->mm, x)
+#define __pud_free_tlb(tlb, x, addr)	tlb_remove_ptdesc((tlb), virt_to_ptdesc(x))
 
 #endif /* __PAGETABLE_PUD_FOLDED */
 
-- 
2.20.1

[PATCH v3 5/7] parisc: mm: enable MMU_GATHER_RCU_TABLE_FREE

[Qi Zheng]

From: Qi Zheng <zhengqi.arch@bytedance.com>

On a 64-bit system, madvise(MADV_DONTNEED) may cause a large number of
empty PTE page table pages (such as 100GB+). To resolve this problem,
first enable MMU_GATHER_RCU_TABLE_FREE to prepare for enabling the
PT_RECLAIM feature, which resolves this problem.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Helge Deller <deller@gmx.de>
---
 arch/parisc/Kconfig           | 1 +
 arch/parisc/include/asm/tlb.h | 4 ++--
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig
index 47fd9662d8005..62d5a89d5c7bc 100644
--- a/arch/parisc/Kconfig
+++ b/arch/parisc/Kconfig
@@ -79,6 +79,7 @@ config PARISC
 	select GENERIC_CLOCKEVENTS
 	select CPU_NO_EFFICIENT_FFS
 	select THREAD_INFO_IN_TASK
+	select MMU_GATHER_RCU_TABLE_FREE
 	select NEED_DMA_MAP_STATE
 	select NEED_SG_DMA_LENGTH
 	select HAVE_ARCH_KGDB
diff --git a/arch/parisc/include/asm/tlb.h b/arch/parisc/include/asm/tlb.h
index 44235f367674d..4501fee0a8fa4 100644
--- a/arch/parisc/include/asm/tlb.h
+++ b/arch/parisc/include/asm/tlb.h
@@ -5,8 +5,8 @@
 #include <asm-generic/tlb.h>
 
 #if CONFIG_PGTABLE_LEVELS == 3
-#define __pmd_free_tlb(tlb, pmd, addr)	pmd_free((tlb)->mm, pmd)
+#define __pmd_free_tlb(tlb, pmd, addr)	tlb_remove_ptdesc((tlb), virt_to_ptdesc(pmd))
 #endif
-#define __pte_free_tlb(tlb, pte, addr)	pte_free((tlb)->mm, pte)
+#define __pte_free_tlb(tlb, pte, addr)	tlb_remove_ptdesc((tlb), page_ptdesc(pte))
 
 #endif
-- 
2.20.1

[PATCH v3 6/7] um: mm: enable MMU_GATHER_RCU_TABLE_FREE

[Qi Zheng]

From: Qi Zheng <zhengqi.arch@bytedance.com>

On a 64-bit system, madvise(MADV_DONTNEED) may cause a large number of
empty PTE page table pages (such as 100GB+). To resolve this problem,
first enable MMU_GATHER_RCU_TABLE_FREE to prepare for enabling the
PT_RECLAIM feature, which resolves this problem.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
---
 arch/um/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/um/Kconfig b/arch/um/Kconfig
index 8415d39b0d430..098cda44db225 100644
--- a/arch/um/Kconfig
+++ b/arch/um/Kconfig
@@ -42,6 +42,7 @@ config UML
 	select HAVE_SYSCALL_TRACEPOINTS
 	select THREAD_INFO_IN_TASK
 	select SPARSE_IRQ
+	select MMU_GATHER_RCU_TABLE_FREE
 
 config MMU
 	bool
-- 
2.20.1

[PATCH v3 7/7] mm: make PT_RECLAIM depends on MMU_GATHER_RCU_TABLE_FREE

[Qi Zheng]

From: Qi Zheng <zhengqi.arch@bytedance.com>

The PT_RECLAIM can work on all architectures that support
MMU_GATHER_RCU_TABLE_FREE, so make PT_RECLAIM depends on
MMU_GATHER_RCU_TABLE_FREE.

BTW, change PT_RECLAIM to be enabled by default, since nobody should want
to turn it off.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 arch/x86/Kconfig | 1 -
 mm/Kconfig       | 9 ++-------
 2 files changed, 2 insertions(+), 8 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 80527299f859a..0d22da56a71b0 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -331,7 +331,6 @@ config X86
 	select FUNCTION_ALIGNMENT_4B
 	imply IMA_SECURE_AND_OR_TRUSTED_BOOT    if EFI
 	select HAVE_DYNAMIC_FTRACE_NO_PATCHABLE
-	select ARCH_SUPPORTS_PT_RECLAIM		if X86_64
 	select ARCH_SUPPORTS_SCHED_SMT		if SMP
 	select SCHED_SMT			if SMP
 	select ARCH_SUPPORTS_SCHED_CLUSTER	if SMP
diff --git a/mm/Kconfig b/mm/Kconfig
index bd0ea5454af82..fc00b429b7129 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -1447,14 +1447,9 @@ config ARCH_HAS_USER_SHADOW_STACK
 	  The architecture has hardware support for userspace shadow call
           stacks (eg, x86 CET, arm64 GCS or RISC-V Zicfiss).
 
-config ARCH_SUPPORTS_PT_RECLAIM
-	def_bool n
-
 config PT_RECLAIM
-	bool "reclaim empty user page table pages"
-	default y
-	depends on ARCH_SUPPORTS_PT_RECLAIM && MMU && SMP
-	select MMU_GATHER_RCU_TABLE_FREE
+	def_bool y
+	depends on MMU_GATHER_RCU_TABLE_FREE
 	help
 	  Try to reclaim empty user page table pages in paths other than munmap
 	  and exit_mmap path.
-- 
2.20.1

Re: [PATCH v3 7/7] mm: make PT_RECLAIM depends on MMU_GATHER_RCU_TABLE_FREE

[Wei Yang]

On Wed, Dec 17, 2025 at 05:45:48PM +0800, Qi Zheng wrote:
>From: Qi Zheng <zhengqi.arch@bytedance.com>
>
>The PT_RECLAIM can work on all architectures that support
>MMU_GATHER_RCU_TABLE_FREE, so make PT_RECLAIM depends on
>MMU_GATHER_RCU_TABLE_FREE.
>
>BTW, change PT_RECLAIM to be enabled by default, since nobody should want
>to turn it off.
>
>Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>---
> arch/x86/Kconfig | 1 -
> mm/Kconfig       | 9 ++-------
> 2 files changed, 2 insertions(+), 8 deletions(-)
>
>diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>index 80527299f859a..0d22da56a71b0 100644
>--- a/arch/x86/Kconfig
>+++ b/arch/x86/Kconfig
>@@ -331,7 +331,6 @@ config X86
> 	select FUNCTION_ALIGNMENT_4B
> 	imply IMA_SECURE_AND_OR_TRUSTED_BOOT    if EFI
> 	select HAVE_DYNAMIC_FTRACE_NO_PATCHABLE
>-	select ARCH_SUPPORTS_PT_RECLAIM		if X86_64
> 	select ARCH_SUPPORTS_SCHED_SMT		if SMP
> 	select SCHED_SMT			if SMP
> 	select ARCH_SUPPORTS_SCHED_CLUSTER	if SMP
>diff --git a/mm/Kconfig b/mm/Kconfig
>index bd0ea5454af82..fc00b429b7129 100644
>--- a/mm/Kconfig
>+++ b/mm/Kconfig
>@@ -1447,14 +1447,9 @@ config ARCH_HAS_USER_SHADOW_STACK
> 	  The architecture has hardware support for userspace shadow call
>           stacks (eg, x86 CET, arm64 GCS or RISC-V Zicfiss).
> 
>-config ARCH_SUPPORTS_PT_RECLAIM
>-	def_bool n
>-
> config PT_RECLAIM
>-	bool "reclaim empty user page table pages"
>-	default y
>-	depends on ARCH_SUPPORTS_PT_RECLAIM && MMU && SMP
>-	select MMU_GATHER_RCU_TABLE_FREE
>+	def_bool y
>+	depends on MMU_GATHER_RCU_TABLE_FREE
> 	help
> 	  Try to reclaim empty user page table pages in paths other than munmap
> 	  and exit_mmap path.

Hi, Qi

I am new to PT_RECLAIM, when reading related code I got one question.

Before this patch,  we could have this config combination:

    CONFIG_MMU_GATHER_RCU_TABLE_FREE & !CONFIG_PT_RECLAIM

This means tlb_remove_table_free() is rcu version while tlb_remove_table_one()
is semi rcu version.

I am curious could we use rcu version tlb_remove_table_one() for this case?
Use rcu version tlb_remove_table_one() if CONFIG_MMU_GATHER_RCU_TABLE_FREE. Is
there some limitation here?

Thanks in advance for your explanation.


-- 
Wei Yang
Help you, Help me

Re: [PATCH v3 7/7] mm: make PT_RECLAIM depends on MMU_GATHER_RCU_TABLE_FREE

[Qi Zheng]

On 12/31/25 5:42 PM, Wei Yang wrote:
> On Wed, Dec 17, 2025 at 05:45:48PM +0800, Qi Zheng wrote:
>> From: Qi Zheng <zhengqi.arch@bytedance.com>
>>
>> The PT_RECLAIM can work on all architectures that support
>> MMU_GATHER_RCU_TABLE_FREE, so make PT_RECLAIM depends on
>> MMU_GATHER_RCU_TABLE_FREE.
>>
>> BTW, change PT_RECLAIM to be enabled by default, since nobody should want
>> to turn it off.
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>> ---
>> arch/x86/Kconfig | 1 -
>> mm/Kconfig       | 9 ++-------
>> 2 files changed, 2 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index 80527299f859a..0d22da56a71b0 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -331,7 +331,6 @@ config X86
>> 	select FUNCTION_ALIGNMENT_4B
>> 	imply IMA_SECURE_AND_OR_TRUSTED_BOOT    if EFI
>> 	select HAVE_DYNAMIC_FTRACE_NO_PATCHABLE
>> -	select ARCH_SUPPORTS_PT_RECLAIM		if X86_64
>> 	select ARCH_SUPPORTS_SCHED_SMT		if SMP
>> 	select SCHED_SMT			if SMP
>> 	select ARCH_SUPPORTS_SCHED_CLUSTER	if SMP
>> diff --git a/mm/Kconfig b/mm/Kconfig
>> index bd0ea5454af82..fc00b429b7129 100644
>> --- a/mm/Kconfig
>> +++ b/mm/Kconfig
>> @@ -1447,14 +1447,9 @@ config ARCH_HAS_USER_SHADOW_STACK
>> 	  The architecture has hardware support for userspace shadow call
>>            stacks (eg, x86 CET, arm64 GCS or RISC-V Zicfiss).
>>
>> -config ARCH_SUPPORTS_PT_RECLAIM
>> -	def_bool n
>> -
>> config PT_RECLAIM
>> -	bool "reclaim empty user page table pages"
>> -	default y
>> -	depends on ARCH_SUPPORTS_PT_RECLAIM && MMU && SMP
>> -	select MMU_GATHER_RCU_TABLE_FREE
>> +	def_bool y
>> +	depends on MMU_GATHER_RCU_TABLE_FREE
>> 	help
>> 	  Try to reclaim empty user page table pages in paths other than munmap
>> 	  and exit_mmap path.
> 
> Hi, Qi
> 
> I am new to PT_RECLAIM, when reading related code I got one question.
> 
> Before this patch,  we could have this config combination:
> 
>      CONFIG_MMU_GATHER_RCU_TABLE_FREE & !CONFIG_PT_RECLAIM
> 
> This means tlb_remove_table_free() is rcu version while tlb_remove_table_one()
> is semi rcu version.
> 
> I am curious could we use rcu version tlb_remove_table_one() for this case?
> Use rcu version tlb_remove_table_one() if CONFIG_MMU_GATHER_RCU_TABLE_FREE. Is
> there some limitation here?

I think there's no problem. The rcu version can also ensure that the
fast GUP works well.

> 
> Thanks in advance for your explanation.
> 
> 

Re: [PATCH v3 7/7] mm: make PT_RECLAIM depends on MMU_GATHER_RCU_TABLE_FREE

[Wei Yang]

On Wed, Dec 31, 2025 at 05:52:57PM +0800, Qi Zheng wrote:
>
>
>On 12/31/25 5:42 PM, Wei Yang wrote:
>> On Wed, Dec 17, 2025 at 05:45:48PM +0800, Qi Zheng wrote:
>> > From: Qi Zheng <zhengqi.arch@bytedance.com>
>> > 
>> > The PT_RECLAIM can work on all architectures that support
>> > MMU_GATHER_RCU_TABLE_FREE, so make PT_RECLAIM depends on
>> > MMU_GATHER_RCU_TABLE_FREE.
>> > 
>> > BTW, change PT_RECLAIM to be enabled by default, since nobody should want
>> > to turn it off.
>> > 
>> > Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>> > ---
>> > arch/x86/Kconfig | 1 -
>> > mm/Kconfig       | 9 ++-------
>> > 2 files changed, 2 insertions(+), 8 deletions(-)
>> > 
>> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> > index 80527299f859a..0d22da56a71b0 100644
>> > --- a/arch/x86/Kconfig
>> > +++ b/arch/x86/Kconfig
>> > @@ -331,7 +331,6 @@ config X86
>> > 	select FUNCTION_ALIGNMENT_4B
>> > 	imply IMA_SECURE_AND_OR_TRUSTED_BOOT    if EFI
>> > 	select HAVE_DYNAMIC_FTRACE_NO_PATCHABLE
>> > -	select ARCH_SUPPORTS_PT_RECLAIM		if X86_64
>> > 	select ARCH_SUPPORTS_SCHED_SMT		if SMP
>> > 	select SCHED_SMT			if SMP
>> > 	select ARCH_SUPPORTS_SCHED_CLUSTER	if SMP
>> > diff --git a/mm/Kconfig b/mm/Kconfig
>> > index bd0ea5454af82..fc00b429b7129 100644
>> > --- a/mm/Kconfig
>> > +++ b/mm/Kconfig
>> > @@ -1447,14 +1447,9 @@ config ARCH_HAS_USER_SHADOW_STACK
>> > 	  The architecture has hardware support for userspace shadow call
>> >            stacks (eg, x86 CET, arm64 GCS or RISC-V Zicfiss).
>> > 
>> > -config ARCH_SUPPORTS_PT_RECLAIM
>> > -	def_bool n
>> > -
>> > config PT_RECLAIM
>> > -	bool "reclaim empty user page table pages"
>> > -	default y
>> > -	depends on ARCH_SUPPORTS_PT_RECLAIM && MMU && SMP
>> > -	select MMU_GATHER_RCU_TABLE_FREE
>> > +	def_bool y
>> > +	depends on MMU_GATHER_RCU_TABLE_FREE
>> > 	help
>> > 	  Try to reclaim empty user page table pages in paths other than munmap
>> > 	  and exit_mmap path.
>> 
>> Hi, Qi
>> 
>> I am new to PT_RECLAIM, when reading related code I got one question.
>> 
>> Before this patch,  we could have this config combination:
>> 
>>      CONFIG_MMU_GATHER_RCU_TABLE_FREE & !CONFIG_PT_RECLAIM
>> 
>> This means tlb_remove_table_free() is rcu version while tlb_remove_table_one()
>> is semi rcu version.
>> 
>> I am curious could we use rcu version tlb_remove_table_one() for this case?
>> Use rcu version tlb_remove_table_one() if CONFIG_MMU_GATHER_RCU_TABLE_FREE. Is
>> there some limitation here?
>
>I think there's no problem. The rcu version can also ensure that the
>fast GUP works well.
>

Thanks for your quick response :-)

And Happy New Year

So my little suggestion is move the definition of __tlb_remove_table_one()
under CONFIG_MMU_GATHER_RCU_TABLE_FREE. Do you thinks this would be more
clear?

>> 
>> Thanks in advance for your explanation.
>> 
>> 

-- 
Wei Yang
Help you, Help me

Re: [PATCH v3 7/7] mm: make PT_RECLAIM depends on MMU_GATHER_RCU_TABLE_FREE

[David Hildenbrand (Red Hat)]

On 1/1/26 03:07, Wei Yang wrote:
> On Wed, Dec 31, 2025 at 05:52:57PM +0800, Qi Zheng wrote:
>>
>>
>> On 12/31/25 5:42 PM, Wei Yang wrote:
>>> On Wed, Dec 17, 2025 at 05:45:48PM +0800, Qi Zheng wrote:
>>>> From: Qi Zheng <zhengqi.arch@bytedance.com>
>>>>
>>>> The PT_RECLAIM can work on all architectures that support
>>>> MMU_GATHER_RCU_TABLE_FREE, so make PT_RECLAIM depends on
>>>> MMU_GATHER_RCU_TABLE_FREE.
>>>>
>>>> BTW, change PT_RECLAIM to be enabled by default, since nobody should want
>>>> to turn it off.
>>>>
>>>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>>>> ---
>>>> arch/x86/Kconfig | 1 -
>>>> mm/Kconfig       | 9 ++-------
>>>> 2 files changed, 2 insertions(+), 8 deletions(-)
>>>>
>>>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>>>> index 80527299f859a..0d22da56a71b0 100644
>>>> --- a/arch/x86/Kconfig
>>>> +++ b/arch/x86/Kconfig
>>>> @@ -331,7 +331,6 @@ config X86
>>>> 	select FUNCTION_ALIGNMENT_4B
>>>> 	imply IMA_SECURE_AND_OR_TRUSTED_BOOT    if EFI
>>>> 	select HAVE_DYNAMIC_FTRACE_NO_PATCHABLE
>>>> -	select ARCH_SUPPORTS_PT_RECLAIM		if X86_64
>>>> 	select ARCH_SUPPORTS_SCHED_SMT		if SMP
>>>> 	select SCHED_SMT			if SMP
>>>> 	select ARCH_SUPPORTS_SCHED_CLUSTER	if SMP
>>>> diff --git a/mm/Kconfig b/mm/Kconfig
>>>> index bd0ea5454af82..fc00b429b7129 100644
>>>> --- a/mm/Kconfig
>>>> +++ b/mm/Kconfig
>>>> @@ -1447,14 +1447,9 @@ config ARCH_HAS_USER_SHADOW_STACK
>>>> 	  The architecture has hardware support for userspace shadow call
>>>>             stacks (eg, x86 CET, arm64 GCS or RISC-V Zicfiss).
>>>>
>>>> -config ARCH_SUPPORTS_PT_RECLAIM
>>>> -	def_bool n
>>>> -
>>>> config PT_RECLAIM
>>>> -	bool "reclaim empty user page table pages"
>>>> -	default y
>>>> -	depends on ARCH_SUPPORTS_PT_RECLAIM && MMU && SMP
>>>> -	select MMU_GATHER_RCU_TABLE_FREE
>>>> +	def_bool y
>>>> +	depends on MMU_GATHER_RCU_TABLE_FREE
>>>> 	help
>>>> 	  Try to reclaim empty user page table pages in paths other than munmap
>>>> 	  and exit_mmap path.
>>>
>>> Hi, Qi
>>>
>>> I am new to PT_RECLAIM, when reading related code I got one question.
>>>
>>> Before this patch,  we could have this config combination:
>>>
>>>       CONFIG_MMU_GATHER_RCU_TABLE_FREE & !CONFIG_PT_RECLAIM
>>>
>>> This means tlb_remove_table_free() is rcu version while tlb_remove_table_one()
>>> is semi rcu version.
>>>
>>> I am curious could we use rcu version tlb_remove_table_one() for this case?
>>> Use rcu version tlb_remove_table_one() if CONFIG_MMU_GATHER_RCU_TABLE_FREE. Is
>>> there some limitation here?
>>
>> I think there's no problem. The rcu version can also ensure that the
>> fast GUP works well.
>>
> 
> Thanks for your quick response :-)
> 
> And Happy New Year
> 
> So my little suggestion is move the definition of __tlb_remove_table_one()
> under CONFIG_MMU_GATHER_RCU_TABLE_FREE. Do you thinks this would be more
> clear?


Do you mean

diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
index 2faa23d7f8d42..6aeba4bae68d2 100644
--- a/mm/mmu_gather.c
+++ b/mm/mmu_gather.c
@@ -319,7 +319,7 @@ static inline void tlb_table_invalidate(struct 
mmu_gather *tlb)
         }
  }

-#ifdef CONFIG_PT_RECLAIM
+#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
  static inline void __tlb_remove_table_one_rcu(struct rcu_head *head)
  {
         struct ptdesc *ptdesc;

?

-- 
Cheers

David

Re: [PATCH v3 7/7] mm: make PT_RECLAIM depends on MMU_GATHER_RCU_TABLE_FREE

[Wei Yang]

On Mon, Jan 19, 2026 at 11:18:52AM +0100, David Hildenbrand (Red Hat) wrote:
>On 1/1/26 03:07, Wei Yang wrote:
>> On Wed, Dec 31, 2025 at 05:52:57PM +0800, Qi Zheng wrote:
>> > 
>> > 
>> > On 12/31/25 5:42 PM, Wei Yang wrote:
>> > > On Wed, Dec 17, 2025 at 05:45:48PM +0800, Qi Zheng wrote:
>> > > > From: Qi Zheng <zhengqi.arch@bytedance.com>
>> > > > 
>> > > > The PT_RECLAIM can work on all architectures that support
>> > > > MMU_GATHER_RCU_TABLE_FREE, so make PT_RECLAIM depends on
>> > > > MMU_GATHER_RCU_TABLE_FREE.
>> > > > 
>> > > > BTW, change PT_RECLAIM to be enabled by default, since nobody should want
>> > > > to turn it off.
>> > > > 
>> > > > Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>> > > > ---
>> > > > arch/x86/Kconfig | 1 -
>> > > > mm/Kconfig       | 9 ++-------
>> > > > 2 files changed, 2 insertions(+), 8 deletions(-)
>> > > > 
>> > > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> > > > index 80527299f859a..0d22da56a71b0 100644
>> > > > --- a/arch/x86/Kconfig
>> > > > +++ b/arch/x86/Kconfig
>> > > > @@ -331,7 +331,6 @@ config X86
>> > > > 	select FUNCTION_ALIGNMENT_4B
>> > > > 	imply IMA_SECURE_AND_OR_TRUSTED_BOOT    if EFI
>> > > > 	select HAVE_DYNAMIC_FTRACE_NO_PATCHABLE
>> > > > -	select ARCH_SUPPORTS_PT_RECLAIM		if X86_64
>> > > > 	select ARCH_SUPPORTS_SCHED_SMT		if SMP
>> > > > 	select SCHED_SMT			if SMP
>> > > > 	select ARCH_SUPPORTS_SCHED_CLUSTER	if SMP
>> > > > diff --git a/mm/Kconfig b/mm/Kconfig
>> > > > index bd0ea5454af82..fc00b429b7129 100644
>> > > > --- a/mm/Kconfig
>> > > > +++ b/mm/Kconfig
>> > > > @@ -1447,14 +1447,9 @@ config ARCH_HAS_USER_SHADOW_STACK
>> > > > 	  The architecture has hardware support for userspace shadow call
>> > > >             stacks (eg, x86 CET, arm64 GCS or RISC-V Zicfiss).
>> > > > 
>> > > > -config ARCH_SUPPORTS_PT_RECLAIM
>> > > > -	def_bool n
>> > > > -
>> > > > config PT_RECLAIM
>> > > > -	bool "reclaim empty user page table pages"
>> > > > -	default y
>> > > > -	depends on ARCH_SUPPORTS_PT_RECLAIM && MMU && SMP
>> > > > -	select MMU_GATHER_RCU_TABLE_FREE
>> > > > +	def_bool y
>> > > > +	depends on MMU_GATHER_RCU_TABLE_FREE
>> > > > 	help
>> > > > 	  Try to reclaim empty user page table pages in paths other than munmap
>> > > > 	  and exit_mmap path.
>> > > 
>> > > Hi, Qi
>> > > 
>> > > I am new to PT_RECLAIM, when reading related code I got one question.
>> > > 
>> > > Before this patch,  we could have this config combination:
>> > > 
>> > >       CONFIG_MMU_GATHER_RCU_TABLE_FREE & !CONFIG_PT_RECLAIM
>> > > 
>> > > This means tlb_remove_table_free() is rcu version while tlb_remove_table_one()
>> > > is semi rcu version.
>> > > 
>> > > I am curious could we use rcu version tlb_remove_table_one() for this case?
>> > > Use rcu version tlb_remove_table_one() if CONFIG_MMU_GATHER_RCU_TABLE_FREE. Is
>> > > there some limitation here?
>> > 
>> > I think there's no problem. The rcu version can also ensure that the
>> > fast GUP works well.
>> > 
>> 
>> Thanks for your quick response :-)
>> 
>> And Happy New Year
>> 
>> So my little suggestion is move the definition of __tlb_remove_table_one()
>> under CONFIG_MMU_GATHER_RCU_TABLE_FREE. Do you thinks this would be more
>> clear?
>
>
>Do you mean
>
>diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
>index 2faa23d7f8d42..6aeba4bae68d2 100644
>--- a/mm/mmu_gather.c
>+++ b/mm/mmu_gather.c
>@@ -319,7 +319,7 @@ static inline void tlb_table_invalidate(struct mmu_gather
>*tlb)
>        }
> }
>
>-#ifdef CONFIG_PT_RECLAIM
>+#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
> static inline void __tlb_remove_table_one_rcu(struct rcu_head *head)
> {
>        struct ptdesc *ptdesc;
>
>?

Sorry for the late reply.

Yes, and maybe we can move the definition to the 
#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE code block above, then to be next to
tlb_remove_table_free().

So that we always have rcu version when CONFIG_MMU_GATHER_RCU_TABLE_FREE.

>
>-- 
>Cheers
>
>David

-- 
Wei Yang
Help you, Help me

Re: [PATCH v3 7/7] mm: make PT_RECLAIM depends on MMU_GATHER_RCU_TABLE_FREE

[Qi Zheng]

On 1/22/26 10:00 PM, Wei Yang wrote:
> On Mon, Jan 19, 2026 at 11:18:52AM +0100, David Hildenbrand (Red Hat) wrote:
>> On 1/1/26 03:07, Wei Yang wrote:
>>> On Wed, Dec 31, 2025 at 05:52:57PM +0800, Qi Zheng wrote:
>>>>
>>>>
>>>> On 12/31/25 5:42 PM, Wei Yang wrote:
>>>>> On Wed, Dec 17, 2025 at 05:45:48PM +0800, Qi Zheng wrote:
>>>>>> From: Qi Zheng <zhengqi.arch@bytedance.com>
>>>>>>
>>>>>> The PT_RECLAIM can work on all architectures that support
>>>>>> MMU_GATHER_RCU_TABLE_FREE, so make PT_RECLAIM depends on
>>>>>> MMU_GATHER_RCU_TABLE_FREE.
>>>>>>
>>>>>> BTW, change PT_RECLAIM to be enabled by default, since nobody should want
>>>>>> to turn it off.
>>>>>>
>>>>>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>>>>>> ---
>>>>>> arch/x86/Kconfig | 1 -
>>>>>> mm/Kconfig       | 9 ++-------
>>>>>> 2 files changed, 2 insertions(+), 8 deletions(-)
>>>>>>
>>>>>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>>>>>> index 80527299f859a..0d22da56a71b0 100644
>>>>>> --- a/arch/x86/Kconfig
>>>>>> +++ b/arch/x86/Kconfig
>>>>>> @@ -331,7 +331,6 @@ config X86
>>>>>> 	select FUNCTION_ALIGNMENT_4B
>>>>>> 	imply IMA_SECURE_AND_OR_TRUSTED_BOOT    if EFI
>>>>>> 	select HAVE_DYNAMIC_FTRACE_NO_PATCHABLE
>>>>>> -	select ARCH_SUPPORTS_PT_RECLAIM		if X86_64
>>>>>> 	select ARCH_SUPPORTS_SCHED_SMT		if SMP
>>>>>> 	select SCHED_SMT			if SMP
>>>>>> 	select ARCH_SUPPORTS_SCHED_CLUSTER	if SMP
>>>>>> diff --git a/mm/Kconfig b/mm/Kconfig
>>>>>> index bd0ea5454af82..fc00b429b7129 100644
>>>>>> --- a/mm/Kconfig
>>>>>> +++ b/mm/Kconfig
>>>>>> @@ -1447,14 +1447,9 @@ config ARCH_HAS_USER_SHADOW_STACK
>>>>>> 	  The architecture has hardware support for userspace shadow call
>>>>>>              stacks (eg, x86 CET, arm64 GCS or RISC-V Zicfiss).
>>>>>>
>>>>>> -config ARCH_SUPPORTS_PT_RECLAIM
>>>>>> -	def_bool n
>>>>>> -
>>>>>> config PT_RECLAIM
>>>>>> -	bool "reclaim empty user page table pages"
>>>>>> -	default y
>>>>>> -	depends on ARCH_SUPPORTS_PT_RECLAIM && MMU && SMP
>>>>>> -	select MMU_GATHER_RCU_TABLE_FREE
>>>>>> +	def_bool y
>>>>>> +	depends on MMU_GATHER_RCU_TABLE_FREE
>>>>>> 	help
>>>>>> 	  Try to reclaim empty user page table pages in paths other than munmap
>>>>>> 	  and exit_mmap path.
>>>>>
>>>>> Hi, Qi
>>>>>
>>>>> I am new to PT_RECLAIM, when reading related code I got one question.
>>>>>
>>>>> Before this patch,  we could have this config combination:
>>>>>
>>>>>        CONFIG_MMU_GATHER_RCU_TABLE_FREE & !CONFIG_PT_RECLAIM
>>>>>
>>>>> This means tlb_remove_table_free() is rcu version while tlb_remove_table_one()
>>>>> is semi rcu version.
>>>>>
>>>>> I am curious could we use rcu version tlb_remove_table_one() for this case?
>>>>> Use rcu version tlb_remove_table_one() if CONFIG_MMU_GATHER_RCU_TABLE_FREE. Is
>>>>> there some limitation here?
>>>>
>>>> I think there's no problem. The rcu version can also ensure that the
>>>> fast GUP works well.
>>>>
>>>
>>> Thanks for your quick response :-)
>>>
>>> And Happy New Year
>>>
>>> So my little suggestion is move the definition of __tlb_remove_table_one()
>>> under CONFIG_MMU_GATHER_RCU_TABLE_FREE. Do you thinks this would be more
>>> clear?
>>
>>
>> Do you mean
>>
>> diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
>> index 2faa23d7f8d42..6aeba4bae68d2 100644
>> --- a/mm/mmu_gather.c
>> +++ b/mm/mmu_gather.c
>> @@ -319,7 +319,7 @@ static inline void tlb_table_invalidate(struct mmu_gather
>> *tlb)
>>         }
>> }
>>
>> -#ifdef CONFIG_PT_RECLAIM
>> +#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
>> static inline void __tlb_remove_table_one_rcu(struct rcu_head *head)
>> {
>>         struct ptdesc *ptdesc;
>>
>> ?
> 
> Sorry for the late reply.
> 
> Yes, and maybe we can move the definition to the
> #ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE code block above, then to be next to
> tlb_remove_table_free().
> 
> So that we always have rcu version when CONFIG_MMU_GATHER_RCU_TABLE_FREE.

LGTM, could you help submit an official patch?

Thanks,
Qi

> 
>>
>> -- 
>> Cheers
>>
>> David
> 

Re: [PATCH v3 7/7] mm: make PT_RECLAIM depends on MMU_GATHER_RCU_TABLE_FREE

[Wei Yang]

On Fri, Jan 23, 2026 at 11:21:50AM +0800, Qi Zheng wrote:
>
>
>On 1/22/26 10:00 PM, Wei Yang wrote:
>> On Mon, Jan 19, 2026 at 11:18:52AM +0100, David Hildenbrand (Red Hat) wrote:
>> > On 1/1/26 03:07, Wei Yang wrote:
>> > > On Wed, Dec 31, 2025 at 05:52:57PM +0800, Qi Zheng wrote:
>> > > > 
>> > > > 
>> > > > On 12/31/25 5:42 PM, Wei Yang wrote:
>> > > > > On Wed, Dec 17, 2025 at 05:45:48PM +0800, Qi Zheng wrote:
>> > > > > > From: Qi Zheng <zhengqi.arch@bytedance.com>
>> > > > > > 
>> > > > > > The PT_RECLAIM can work on all architectures that support
>> > > > > > MMU_GATHER_RCU_TABLE_FREE, so make PT_RECLAIM depends on
>> > > > > > MMU_GATHER_RCU_TABLE_FREE.
>> > > > > > 
>> > > > > > BTW, change PT_RECLAIM to be enabled by default, since nobody should want
>> > > > > > to turn it off.
>> > > > > > 
>> > > > > > Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>> > > > > > ---
>> > > > > > arch/x86/Kconfig | 1 -
>> > > > > > mm/Kconfig       | 9 ++-------
>> > > > > > 2 files changed, 2 insertions(+), 8 deletions(-)
>> > > > > > 
>> > > > > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> > > > > > index 80527299f859a..0d22da56a71b0 100644
>> > > > > > --- a/arch/x86/Kconfig
>> > > > > > +++ b/arch/x86/Kconfig
>> > > > > > @@ -331,7 +331,6 @@ config X86
>> > > > > > 	select FUNCTION_ALIGNMENT_4B
>> > > > > > 	imply IMA_SECURE_AND_OR_TRUSTED_BOOT    if EFI
>> > > > > > 	select HAVE_DYNAMIC_FTRACE_NO_PATCHABLE
>> > > > > > -	select ARCH_SUPPORTS_PT_RECLAIM		if X86_64
>> > > > > > 	select ARCH_SUPPORTS_SCHED_SMT		if SMP
>> > > > > > 	select SCHED_SMT			if SMP
>> > > > > > 	select ARCH_SUPPORTS_SCHED_CLUSTER	if SMP
>> > > > > > diff --git a/mm/Kconfig b/mm/Kconfig
>> > > > > > index bd0ea5454af82..fc00b429b7129 100644
>> > > > > > --- a/mm/Kconfig
>> > > > > > +++ b/mm/Kconfig
>> > > > > > @@ -1447,14 +1447,9 @@ config ARCH_HAS_USER_SHADOW_STACK
>> > > > > > 	  The architecture has hardware support for userspace shadow call
>> > > > > >              stacks (eg, x86 CET, arm64 GCS or RISC-V Zicfiss).
>> > > > > > 
>> > > > > > -config ARCH_SUPPORTS_PT_RECLAIM
>> > > > > > -	def_bool n
>> > > > > > -
>> > > > > > config PT_RECLAIM
>> > > > > > -	bool "reclaim empty user page table pages"
>> > > > > > -	default y
>> > > > > > -	depends on ARCH_SUPPORTS_PT_RECLAIM && MMU && SMP
>> > > > > > -	select MMU_GATHER_RCU_TABLE_FREE
>> > > > > > +	def_bool y
>> > > > > > +	depends on MMU_GATHER_RCU_TABLE_FREE
>> > > > > > 	help
>> > > > > > 	  Try to reclaim empty user page table pages in paths other than munmap
>> > > > > > 	  and exit_mmap path.
>> > > > > 
>> > > > > Hi, Qi
>> > > > > 
>> > > > > I am new to PT_RECLAIM, when reading related code I got one question.
>> > > > > 
>> > > > > Before this patch,  we could have this config combination:
>> > > > > 
>> > > > >        CONFIG_MMU_GATHER_RCU_TABLE_FREE & !CONFIG_PT_RECLAIM
>> > > > > 
>> > > > > This means tlb_remove_table_free() is rcu version while tlb_remove_table_one()
>> > > > > is semi rcu version.
>> > > > > 
>> > > > > I am curious could we use rcu version tlb_remove_table_one() for this case?
>> > > > > Use rcu version tlb_remove_table_one() if CONFIG_MMU_GATHER_RCU_TABLE_FREE. Is
>> > > > > there some limitation here?
>> > > > 
>> > > > I think there's no problem. The rcu version can also ensure that the
>> > > > fast GUP works well.
>> > > > 
>> > > 
>> > > Thanks for your quick response :-)
>> > > 
>> > > And Happy New Year
>> > > 
>> > > So my little suggestion is move the definition of __tlb_remove_table_one()
>> > > under CONFIG_MMU_GATHER_RCU_TABLE_FREE. Do you thinks this would be more
>> > > clear?
>> > 
>> > 
>> > Do you mean
>> > 
>> > diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
>> > index 2faa23d7f8d42..6aeba4bae68d2 100644
>> > --- a/mm/mmu_gather.c
>> > +++ b/mm/mmu_gather.c
>> > @@ -319,7 +319,7 @@ static inline void tlb_table_invalidate(struct mmu_gather
>> > *tlb)
>> >         }
>> > }
>> > 
>> > -#ifdef CONFIG_PT_RECLAIM
>> > +#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
>> > static inline void __tlb_remove_table_one_rcu(struct rcu_head *head)
>> > {
>> >         struct ptdesc *ptdesc;
>> > 
>> > ?
>> 
>> Sorry for the late reply.
>> 
>> Yes, and maybe we can move the definition to the
>> #ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE code block above, then to be next to
>> tlb_remove_table_free().
>> 
>> So that we always have rcu version when CONFIG_MMU_GATHER_RCU_TABLE_FREE.
>
>LGTM, could you help submit an official patch?
>

Sure.

Since this is trivial cleanup, I will post it till next merge window.

>Thanks,
>Qi
>
>> 
>> > 
>> > -- 
>> > Cheers
>> > 
>> > David
>> 

-- 
Wei Yang
Help you, Help me

Re: [PATCH v3 7/7] mm: make PT_RECLAIM depends on MMU_GATHER_RCU_TABLE_FREE

[David Hildenbrand (Red Hat)]

On 12/17/25 10:45, Qi Zheng wrote:
> From: Qi Zheng <zhengqi.arch@bytedance.com>
> 
> The PT_RECLAIM can work on all architectures that support
> MMU_GATHER_RCU_TABLE_FREE, so make PT_RECLAIM depends on
> MMU_GATHER_RCU_TABLE_FREE.
> 
> BTW, change PT_RECLAIM to be enabled by default, since nobody should want
> to turn it off.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> ---
>   arch/x86/Kconfig | 1 -
>   mm/Kconfig       | 9 ++-------
>   2 files changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 80527299f859a..0d22da56a71b0 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -331,7 +331,6 @@ config X86
>   	select FUNCTION_ALIGNMENT_4B
>   	imply IMA_SECURE_AND_OR_TRUSTED_BOOT    if EFI
>   	select HAVE_DYNAMIC_FTRACE_NO_PATCHABLE
> -	select ARCH_SUPPORTS_PT_RECLAIM		if X86_64
>   	select ARCH_SUPPORTS_SCHED_SMT		if SMP
>   	select SCHED_SMT			if SMP
>   	select ARCH_SUPPORTS_SCHED_CLUSTER	if SMP
> diff --git a/mm/Kconfig b/mm/Kconfig
> index bd0ea5454af82..fc00b429b7129 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -1447,14 +1447,9 @@ config ARCH_HAS_USER_SHADOW_STACK
>   	  The architecture has hardware support for userspace shadow call
>             stacks (eg, x86 CET, arm64 GCS or RISC-V Zicfiss).
>   
> -config ARCH_SUPPORTS_PT_RECLAIM
> -	def_bool n
> -
>   config PT_RECLAIM
> -	bool "reclaim empty user page table pages"
> -	default y
> -	depends on ARCH_SUPPORTS_PT_RECLAIM && MMU && SMP
> -	select MMU_GATHER_RCU_TABLE_FREE
> +	def_bool y
> +	depends on MMU_GATHER_RCU_TABLE_FREE
>   	help
>   	  Try to reclaim empty user page table pages in paths other than munmap
>   	  and exit_mmap path.

This patch seems to make s390x compilations sometimes unhappy:

Unverified Warning (likely false positive, kindly check if interested):

     mm/memory.c:1911 zap_pte_range() error: uninitialized symbol 'pmdval'.

Warning ids grouped by kconfigs:

recent_errors
`-- s390-randconfig-r072-20260117
     `-- mm-memory.c-zap_pte_range()-error:uninitialized-symbol-pmdval-.

I assume the compiler is not able to figure out that only when
try_get_and_clear_pmd() returns false that pmdval could be uninitialized.

Maybe it has to do with LTO?


After all, that function resides in a different compilation unit.

Which makes me wonder whether we want to just move try_get_and_clear_pmd()
and reclaim_pt_is_enabled() to internal.h or even just memory.c?

But then, maybe we could remove pt_reclaim.c completely and just have
try_to_free_pte() in memory.c as well?


I would just do the following cleanup:

 From cfe97092f71fcc88f729f07ee0bc6816e3e398f0 Mon Sep 17 00:00:00 2001
From: "David Hildenbrand (Red Hat)" <david@kernel.org>
Date: Sun, 18 Jan 2026 12:20:55 +0100
Subject: [PATCH] mm: move pte table reclaim code to memory.c

Let's move the code and clean it up a bit along the way.

Signed-off-by: David Hildenbrand (Red Hat) <david@kernel.org>
---
  MAINTAINERS     |  1 -
  mm/internal.h   | 18 -------------
  mm/memory.c     | 70 ++++++++++++++++++++++++++++++++++++++++++-----
  mm/pt_reclaim.c | 72 -------------------------------------------------
  4 files changed, 64 insertions(+), 97 deletions(-)
  delete mode 100644 mm/pt_reclaim.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 11720728d92f2..28e8e28bca3e5 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -16692,7 +16692,6 @@ R:	Shakeel Butt <shakeel.butt@linux.dev>
  R:	Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
  L:	linux-mm@kvack.org
  S:	Maintained
-F:	mm/pt_reclaim.c
  F:	mm/vmscan.c
  F:	mm/workingset.c
  
diff --git a/mm/internal.h b/mm/internal.h
index 9508dbaf47cd4..ef71a1d9991f2 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1745,24 +1745,6 @@ int walk_page_range_debug(struct mm_struct *mm, unsigned long start,
  			  unsigned long end, const struct mm_walk_ops *ops,
  			  pgd_t *pgd, void *private);
  
-/* pt_reclaim.c */
-bool try_get_and_clear_pmd(struct mm_struct *mm, pmd_t *pmd, pmd_t *pmdval);
-void free_pte(struct mm_struct *mm, unsigned long addr, struct mmu_gather *tlb,
-	      pmd_t pmdval);
-void try_to_free_pte(struct mm_struct *mm, pmd_t *pmd, unsigned long addr,
-		     struct mmu_gather *tlb);
-
-#ifdef CONFIG_PT_RECLAIM
-bool reclaim_pt_is_enabled(unsigned long start, unsigned long end,
-			   struct zap_details *details);
-#else
-static inline bool reclaim_pt_is_enabled(unsigned long start, unsigned long end,
-					 struct zap_details *details)
-{
-	return false;
-}
-#endif /* CONFIG_PT_RECLAIM */
-
  void dup_mm_exe_file(struct mm_struct *mm, struct mm_struct *oldmm);
  int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm);
  
diff --git a/mm/memory.c b/mm/memory.c
index f2e9e05388743..a09226761a07f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1824,11 +1824,68 @@ static inline int do_zap_pte_range(struct mmu_gather *tlb,
  	return nr;
  }
  
+static bool pte_table_reclaim_enabled(unsigned long start, unsigned long end,
+		struct zap_details *details)
+{
+	if (!IS_ENABLED(CONFIG_PT_RECLAIM))
+		return false;
+	return details && details->reclaim_pt && (end - start >= PMD_SIZE);
+}
+
+static bool zap_empty_pte_table(struct mm_struct *mm, pmd_t *pmd, pmd_t *pmdval)
+{
+	spinlock_t *pml = pmd_lockptr(mm, pmd);
+
+	if (!spin_trylock(pml))
+		return false;
+
+	*pmdval = pmdp_get_lockless(pmd);
+	pmd_clear(pmd);
+	spin_unlock(pml);
+
+	return true;
+}
+
+static bool zap_pte_table_if_empty(struct mm_struct *mm, pmd_t *pmd,
+		unsigned long addr, pmd_t *pmdval)
+{
+	spinlock_t *pml, *ptl = NULL;
+	pte_t *start_pte, *pte;
+	int i;
+
+	pml = pmd_lock(mm, pmd);
+	start_pte = pte_offset_map_rw_nolock(mm, pmd, addr, pmdval, &ptl);
+	if (!start_pte)
+		goto out_ptl;
+	if (ptl != pml)
+		spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
+
+	for (i = 0, pte = start_pte; i < PTRS_PER_PTE; i++, pte++) {
+		if (!pte_none(ptep_get(pte)))
+			goto out_ptl;
+	}
+	pte_unmap(start_pte);
+
+	pmd_clear(pmd);
+
+	if (ptl != pml)
+		spin_unlock(ptl);
+	spin_unlock(pml);
+	return true;
+out_ptl:
+	if (start_pte)
+		pte_unmap_unlock(start_pte, ptl);
+	if (ptl != pml)
+		spin_unlock(pml);
+	return false;
+}
+
  static unsigned long zap_pte_range(struct mmu_gather *tlb,
  				struct vm_area_struct *vma, pmd_t *pmd,
  				unsigned long addr, unsigned long end,
  				struct zap_details *details)
  {
+	bool can_reclaim_pt = pte_table_reclaim_enabled(addr, end, details);
  	bool force_flush = false, force_break = false;
  	struct mm_struct *mm = tlb->mm;
  	int rss[NR_MM_COUNTERS];
@@ -1837,7 +1894,6 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
  	pte_t *pte;
  	pmd_t pmdval;
  	unsigned long start = addr;
-	bool can_reclaim_pt = reclaim_pt_is_enabled(start, end, details);
  	bool direct_reclaim = true;
  	int nr;
  
@@ -1878,7 +1934,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
  	 * from being repopulated by another thread.
  	 */
  	if (can_reclaim_pt && direct_reclaim && addr == end)
-		direct_reclaim = try_get_and_clear_pmd(mm, pmd, &pmdval);
+		direct_reclaim = zap_empty_pte_table(mm, pmd, &pmdval);
  
  	add_mm_rss_vec(mm, rss);
  	lazy_mmu_mode_disable();
@@ -1907,10 +1963,12 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
  	}
  
  	if (can_reclaim_pt) {
-		if (direct_reclaim)
-			free_pte(mm, start, tlb, pmdval);
-		else
-			try_to_free_pte(mm, pmd, start, tlb);
+		if (!direct_reclaim)
+			direct_reclaim = zap_pte_table_if_empty(mm, pmd, start, &pmdval);
+		if (direct_reclaim) {
+			pte_free_tlb(tlb, pmd_pgtable(pmdval), addr);
+			mm_dec_nr_ptes(mm);
+		}
  	}
  
  	return addr;
diff --git a/mm/pt_reclaim.c b/mm/pt_reclaim.c
deleted file mode 100644
index 46771cfff8239..0000000000000
--- a/mm/pt_reclaim.c
+++ /dev/null
@@ -1,72 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-#include <linux/hugetlb.h>
-#include <linux/pgalloc.h>
-
-#include <asm/tlb.h>
-
-#include "internal.h"
-
-bool reclaim_pt_is_enabled(unsigned long start, unsigned long end,
-			   struct zap_details *details)
-{
-	return details && details->reclaim_pt && (end - start >= PMD_SIZE);
-}
-
-bool try_get_and_clear_pmd(struct mm_struct *mm, pmd_t *pmd, pmd_t *pmdval)
-{
-	spinlock_t *pml = pmd_lockptr(mm, pmd);
-
-	if (!spin_trylock(pml))
-		return false;
-
-	*pmdval = pmdp_get_lockless(pmd);
-	pmd_clear(pmd);
-	spin_unlock(pml);
-
-	return true;
-}
-
-void free_pte(struct mm_struct *mm, unsigned long addr, struct mmu_gather *tlb,
-	      pmd_t pmdval)
-{
-	pte_free_tlb(tlb, pmd_pgtable(pmdval), addr);
-	mm_dec_nr_ptes(mm);
-}
-
-void try_to_free_pte(struct mm_struct *mm, pmd_t *pmd, unsigned long addr,
-		     struct mmu_gather *tlb)
-{
-	pmd_t pmdval;
-	spinlock_t *pml, *ptl = NULL;
-	pte_t *start_pte, *pte;
-	int i;
-
-	pml = pmd_lock(mm, pmd);
-	start_pte = pte_offset_map_rw_nolock(mm, pmd, addr, &pmdval, &ptl);
-	if (!start_pte)
-		goto out_ptl;
-	if (ptl != pml)
-		spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
-
-	/* Check if it is empty PTE page */
-	for (i = 0, pte = start_pte; i < PTRS_PER_PTE; i++, pte++) {
-		if (!pte_none(ptep_get(pte)))
-			goto out_ptl;
-	}
-	pte_unmap(start_pte);
-
-	pmd_clear(pmd);
-
-	if (ptl != pml)
-		spin_unlock(ptl);
-	spin_unlock(pml);
-
-	free_pte(mm, addr, tlb, pmdval);
-
-	return;
-out_ptl:
-	if (start_pte)
-		pte_unmap_unlock(start_pte, ptl);
-	if (ptl != pml)
-		spin_unlock(pml);
-}
-- 
2.52.0


Completely untested, of course.

-- 
Cheers

David

Re: [PATCH v3 7/7] mm: make PT_RECLAIM depends on MMU_GATHER_RCU_TABLE_FREE

[Qi Zheng]

On 1/18/26 7:23 PM, David Hildenbrand (Red Hat) wrote:
> On 12/17/25 10:45, Qi Zheng wrote:
>> From: Qi Zheng <zhengqi.arch@bytedance.com>
>>
>> The PT_RECLAIM can work on all architectures that support
>> MMU_GATHER_RCU_TABLE_FREE, so make PT_RECLAIM depends on
>> MMU_GATHER_RCU_TABLE_FREE.
>>
>> BTW, change PT_RECLAIM to be enabled by default, since nobody should want
>> to turn it off.
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>> ---
>>   arch/x86/Kconfig | 1 -
>>   mm/Kconfig       | 9 ++-------
>>   2 files changed, 2 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index 80527299f859a..0d22da56a71b0 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -331,7 +331,6 @@ config X86
>>       select FUNCTION_ALIGNMENT_4B
>>       imply IMA_SECURE_AND_OR_TRUSTED_BOOT    if EFI
>>       select HAVE_DYNAMIC_FTRACE_NO_PATCHABLE
>> -    select ARCH_SUPPORTS_PT_RECLAIM        if X86_64
>>       select ARCH_SUPPORTS_SCHED_SMT        if SMP
>>       select SCHED_SMT            if SMP
>>       select ARCH_SUPPORTS_SCHED_CLUSTER    if SMP
>> diff --git a/mm/Kconfig b/mm/Kconfig
>> index bd0ea5454af82..fc00b429b7129 100644
>> --- a/mm/Kconfig
>> +++ b/mm/Kconfig
>> @@ -1447,14 +1447,9 @@ config ARCH_HAS_USER_SHADOW_STACK
>>         The architecture has hardware support for userspace shadow call
>>             stacks (eg, x86 CET, arm64 GCS or RISC-V Zicfiss).
>> -config ARCH_SUPPORTS_PT_RECLAIM
>> -    def_bool n
>> -
>>   config PT_RECLAIM
>> -    bool "reclaim empty user page table pages"
>> -    default y
>> -    depends on ARCH_SUPPORTS_PT_RECLAIM && MMU && SMP
>> -    select MMU_GATHER_RCU_TABLE_FREE
>> +    def_bool y
>> +    depends on MMU_GATHER_RCU_TABLE_FREE
>>       help
>>         Try to reclaim empty user page table pages in paths other than 
>> munmap
>>         and exit_mmap path.
> 
> This patch seems to make s390x compilations sometimes unhappy:
> 
> Unverified Warning (likely false positive, kindly check if interested):

I believe it is a false positive.

> 
>      mm/memory.c:1911 zap_pte_range() error: uninitialized symbol 'pmdval'.
> 
> Warning ids grouped by kconfigs:
> 
> recent_errors
> `-- s390-randconfig-r072-20260117
>      `-- mm-memory.c-zap_pte_range()-error:uninitialized-symbol-pmdval-.
> 
> I assume the compiler is not able to figure out that only when
> try_get_and_clear_pmd() returns false that pmdval could be uninitialized.
> 
> Maybe it has to do with LTO?
> 
> 
> After all, that function resides in a different compilation unit.
> 
> Which makes me wonder whether we want to just move try_get_and_clear_pmd()
> and reclaim_pt_is_enabled() to internal.h or even just memory.c?
> 
> But then, maybe we could remove pt_reclaim.c completely and just have
> try_to_free_pte() in memory.c as well?
> 
> 
> I would just do the following cleanup:
> 
>  From cfe97092f71fcc88f729f07ee0bc6816e3e398f0 Mon Sep 17 00:00:00 2001
> From: "David Hildenbrand (Red Hat)" <david@kernel.org>
> Date: Sun, 18 Jan 2026 12:20:55 +0100
> Subject: [PATCH] mm: move pte table reclaim code to memory.c
> 
> Let's move the code and clean it up a bit along the way.
> 
> Signed-off-by: David Hildenbrand (Red Hat) <david@kernel.org>
> ---
>   MAINTAINERS     |  1 -
>   mm/internal.h   | 18 -------------
>   mm/memory.c     | 70 ++++++++++++++++++++++++++++++++++++++++++-----
>   mm/pt_reclaim.c | 72 -------------------------------------------------
>   4 files changed, 64 insertions(+), 97 deletions(-)
>   delete mode 100644 mm/pt_reclaim.c

Make sense, and LGTM. The reason it was placed in mm/pt_reclaim.c before
was because there would be other paths calling these functions in the
future. However, it can be separated out or put into a header file when
there are actually such callers.

would you be willing to send out an official patch?

Thanks,
Qi

> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 11720728d92f2..28e8e28bca3e5 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -16692,7 +16692,6 @@ R:    Shakeel Butt <shakeel.butt@linux.dev>
>   R:    Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
>   L:    linux-mm@kvack.org
>   S:    Maintained
> -F:    mm/pt_reclaim.c
>   F:    mm/vmscan.c
>   F:    mm/workingset.c
> 
> diff --git a/mm/internal.h b/mm/internal.h
> index 9508dbaf47cd4..ef71a1d9991f2 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -1745,24 +1745,6 @@ int walk_page_range_debug(struct mm_struct *mm, 
> unsigned long start,
>                 unsigned long end, const struct mm_walk_ops *ops,
>                 pgd_t *pgd, void *private);
> 
> -/* pt_reclaim.c */
> -bool try_get_and_clear_pmd(struct mm_struct *mm, pmd_t *pmd, pmd_t 
> *pmdval);
> -void free_pte(struct mm_struct *mm, unsigned long addr, struct 
> mmu_gather *tlb,
> -          pmd_t pmdval);
> -void try_to_free_pte(struct mm_struct *mm, pmd_t *pmd, unsigned long addr,
> -             struct mmu_gather *tlb);
> -
> -#ifdef CONFIG_PT_RECLAIM
> -bool reclaim_pt_is_enabled(unsigned long start, unsigned long end,
> -               struct zap_details *details);
> -#else
> -static inline bool reclaim_pt_is_enabled(unsigned long start, unsigned 
> long end,
> -                     struct zap_details *details)
> -{
> -    return false;
> -}
> -#endif /* CONFIG_PT_RECLAIM */
> -
>   void dup_mm_exe_file(struct mm_struct *mm, struct mm_struct *oldmm);
>   int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm);
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index f2e9e05388743..a09226761a07f 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1824,11 +1824,68 @@ static inline int do_zap_pte_range(struct 
> mmu_gather *tlb,
>       return nr;
>   }
> 
> +static bool pte_table_reclaim_enabled(unsigned long start, unsigned 
> long end,
> +        struct zap_details *details)
> +{
> +    if (!IS_ENABLED(CONFIG_PT_RECLAIM))
> +        return false;
> +    return details && details->reclaim_pt && (end - start >= PMD_SIZE);
> +}
> +
> +static bool zap_empty_pte_table(struct mm_struct *mm, pmd_t *pmd, pmd_t 
> *pmdval)
> +{
> +    spinlock_t *pml = pmd_lockptr(mm, pmd);
> +
> +    if (!spin_trylock(pml))
> +        return false;
> +
> +    *pmdval = pmdp_get_lockless(pmd);
> +    pmd_clear(pmd);
> +    spin_unlock(pml);
> +
> +    return true;
> +}
> +
> +static bool zap_pte_table_if_empty(struct mm_struct *mm, pmd_t *pmd,
> +        unsigned long addr, pmd_t *pmdval)
> +{
> +    spinlock_t *pml, *ptl = NULL;
> +    pte_t *start_pte, *pte;
> +    int i;
> +
> +    pml = pmd_lock(mm, pmd);
> +    start_pte = pte_offset_map_rw_nolock(mm, pmd, addr, pmdval, &ptl);
> +    if (!start_pte)
> +        goto out_ptl;
> +    if (ptl != pml)
> +        spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
> +
> +    for (i = 0, pte = start_pte; i < PTRS_PER_PTE; i++, pte++) {
> +        if (!pte_none(ptep_get(pte)))
> +            goto out_ptl;
> +    }
> +    pte_unmap(start_pte);
> +
> +    pmd_clear(pmd);
> +
> +    if (ptl != pml)
> +        spin_unlock(ptl);
> +    spin_unlock(pml);
> +    return true;
> +out_ptl:
> +    if (start_pte)
> +        pte_unmap_unlock(start_pte, ptl);
> +    if (ptl != pml)
> +        spin_unlock(pml);
> +    return false;
> +}
> +
>   static unsigned long zap_pte_range(struct mmu_gather *tlb,
>                   struct vm_area_struct *vma, pmd_t *pmd,
>                   unsigned long addr, unsigned long end,
>                   struct zap_details *details)
>   {
> +    bool can_reclaim_pt = pte_table_reclaim_enabled(addr, end, details);
>       bool force_flush = false, force_break = false;
>       struct mm_struct *mm = tlb->mm;
>       int rss[NR_MM_COUNTERS];
> @@ -1837,7 +1894,6 @@ static unsigned long zap_pte_range(struct 
> mmu_gather *tlb,
>       pte_t *pte;
>       pmd_t pmdval;
>       unsigned long start = addr;
> -    bool can_reclaim_pt = reclaim_pt_is_enabled(start, end, details);
>       bool direct_reclaim = true;
>       int nr;
> 
> @@ -1878,7 +1934,7 @@ static unsigned long zap_pte_range(struct 
> mmu_gather *tlb,
>        * from being repopulated by another thread.
>        */
>       if (can_reclaim_pt && direct_reclaim && addr == end)
> -        direct_reclaim = try_get_and_clear_pmd(mm, pmd, &pmdval);
> +        direct_reclaim = zap_empty_pte_table(mm, pmd, &pmdval);
> 
>       add_mm_rss_vec(mm, rss);
>       lazy_mmu_mode_disable();
> @@ -1907,10 +1963,12 @@ static unsigned long zap_pte_range(struct 
> mmu_gather *tlb,
>       }
> 
>       if (can_reclaim_pt) {
> -        if (direct_reclaim)
> -            free_pte(mm, start, tlb, pmdval);
> -        else
> -            try_to_free_pte(mm, pmd, start, tlb);
> +        if (!direct_reclaim)
> +            direct_reclaim = zap_pte_table_if_empty(mm, pmd, start, 
> &pmdval);
> +        if (direct_reclaim) {
> +            pte_free_tlb(tlb, pmd_pgtable(pmdval), addr);
> +            mm_dec_nr_ptes(mm);
> +        }
>       }
> 
>       return addr;
> diff --git a/mm/pt_reclaim.c b/mm/pt_reclaim.c
> deleted file mode 100644
> index 46771cfff8239..0000000000000
> --- a/mm/pt_reclaim.c
> +++ /dev/null
> @@ -1,72 +0,0 @@
> -// SPDX-License-Identifier: GPL-2.0
> -#include <linux/hugetlb.h>
> -#include <linux/pgalloc.h>
> -
> -#include <asm/tlb.h>
> -
> -#include "internal.h"
> -
> -bool reclaim_pt_is_enabled(unsigned long start, unsigned long end,
> -               struct zap_details *details)
> -{
> -    return details && details->reclaim_pt && (end - start >= PMD_SIZE);
> -}
> -
> -bool try_get_and_clear_pmd(struct mm_struct *mm, pmd_t *pmd, pmd_t 
> *pmdval)
> -{
> -    spinlock_t *pml = pmd_lockptr(mm, pmd);
> -
> -    if (!spin_trylock(pml))
> -        return false;
> -
> -    *pmdval = pmdp_get_lockless(pmd);
> -    pmd_clear(pmd);
> -    spin_unlock(pml);
> -
> -    return true;
> -}
> -
> -void free_pte(struct mm_struct *mm, unsigned long addr, struct 
> mmu_gather *tlb,
> -          pmd_t pmdval)
> -{
> -    pte_free_tlb(tlb, pmd_pgtable(pmdval), addr);
> -    mm_dec_nr_ptes(mm);
> -}
> -
> -void try_to_free_pte(struct mm_struct *mm, pmd_t *pmd, unsigned long addr,
> -             struct mmu_gather *tlb)
> -{
> -    pmd_t pmdval;
> -    spinlock_t *pml, *ptl = NULL;
> -    pte_t *start_pte, *pte;
> -    int i;
> -
> -    pml = pmd_lock(mm, pmd);
> -    start_pte = pte_offset_map_rw_nolock(mm, pmd, addr, &pmdval, &ptl);
> -    if (!start_pte)
> -        goto out_ptl;
> -    if (ptl != pml)
> -        spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
> -
> -    /* Check if it is empty PTE page */
> -    for (i = 0, pte = start_pte; i < PTRS_PER_PTE; i++, pte++) {
> -        if (!pte_none(ptep_get(pte)))
> -            goto out_ptl;
> -    }
> -    pte_unmap(start_pte);
> -
> -    pmd_clear(pmd);
> -
> -    if (ptl != pml)
> -        spin_unlock(ptl);
> -    spin_unlock(pml);
> -
> -    free_pte(mm, addr, tlb, pmdval);
> -
> -    return;
> -out_ptl:
> -    if (start_pte)
> -        pte_unmap_unlock(start_pte, ptl);
> -    if (ptl != pml)
> -        spin_unlock(pml);
> -}

Re: [PATCH v3 7/7] mm: make PT_RECLAIM depends on MMU_GATHER_RCU_TABLE_FREE

[David Hildenbrand (Red Hat)]

On 1/19/26 04:50, Qi Zheng wrote:
> 
> 
> On 1/18/26 7:23 PM, David Hildenbrand (Red Hat) wrote:
>> On 12/17/25 10:45, Qi Zheng wrote:
>>> From: Qi Zheng <zhengqi.arch@bytedance.com>
>>>
>>> The PT_RECLAIM can work on all architectures that support
>>> MMU_GATHER_RCU_TABLE_FREE, so make PT_RECLAIM depends on
>>> MMU_GATHER_RCU_TABLE_FREE.
>>>
>>> BTW, change PT_RECLAIM to be enabled by default, since nobody should want
>>> to turn it off.
>>>
>>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>>> ---
>>>    arch/x86/Kconfig | 1 -
>>>    mm/Kconfig       | 9 ++-------
>>>    2 files changed, 2 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>>> index 80527299f859a..0d22da56a71b0 100644
>>> --- a/arch/x86/Kconfig
>>> +++ b/arch/x86/Kconfig
>>> @@ -331,7 +331,6 @@ config X86
>>>        select FUNCTION_ALIGNMENT_4B
>>>        imply IMA_SECURE_AND_OR_TRUSTED_BOOT    if EFI
>>>        select HAVE_DYNAMIC_FTRACE_NO_PATCHABLE
>>> -    select ARCH_SUPPORTS_PT_RECLAIM        if X86_64
>>>        select ARCH_SUPPORTS_SCHED_SMT        if SMP
>>>        select SCHED_SMT            if SMP
>>>        select ARCH_SUPPORTS_SCHED_CLUSTER    if SMP
>>> diff --git a/mm/Kconfig b/mm/Kconfig
>>> index bd0ea5454af82..fc00b429b7129 100644
>>> --- a/mm/Kconfig
>>> +++ b/mm/Kconfig
>>> @@ -1447,14 +1447,9 @@ config ARCH_HAS_USER_SHADOW_STACK
>>>          The architecture has hardware support for userspace shadow call
>>>              stacks (eg, x86 CET, arm64 GCS or RISC-V Zicfiss).
>>> -config ARCH_SUPPORTS_PT_RECLAIM
>>> -    def_bool n
>>> -
>>>    config PT_RECLAIM
>>> -    bool "reclaim empty user page table pages"
>>> -    default y
>>> -    depends on ARCH_SUPPORTS_PT_RECLAIM && MMU && SMP
>>> -    select MMU_GATHER_RCU_TABLE_FREE
>>> +    def_bool y
>>> +    depends on MMU_GATHER_RCU_TABLE_FREE
>>>        help
>>>          Try to reclaim empty user page table pages in paths other than
>>> munmap
>>>          and exit_mmap path.
>>
>> This patch seems to make s390x compilations sometimes unhappy:
>>
>> Unverified Warning (likely false positive, kindly check if interested):
> 
> I believe it is a false positive.
> 
>>
>>       mm/memory.c:1911 zap_pte_range() error: uninitialized symbol 'pmdval'.
>>
>> Warning ids grouped by kconfigs:
>>
>> recent_errors
>> `-- s390-randconfig-r072-20260117
>>       `-- mm-memory.c-zap_pte_range()-error:uninitialized-symbol-pmdval-.
>>
>> I assume the compiler is not able to figure out that only when
>> try_get_and_clear_pmd() returns false that pmdval could be uninitialized.
>>
>> Maybe it has to do with LTO?
>>
>>
>> After all, that function resides in a different compilation unit.
>>
>> Which makes me wonder whether we want to just move try_get_and_clear_pmd()
>> and reclaim_pt_is_enabled() to internal.h or even just memory.c?
>>
>> But then, maybe we could remove pt_reclaim.c completely and just have
>> try_to_free_pte() in memory.c as well?
>>
>>
>> I would just do the following cleanup:
>>
>>   From cfe97092f71fcc88f729f07ee0bc6816e3e398f0 Mon Sep 17 00:00:00 2001
>> From: "David Hildenbrand (Red Hat)" <david@kernel.org>
>> Date: Sun, 18 Jan 2026 12:20:55 +0100
>> Subject: [PATCH] mm: move pte table reclaim code to memory.c
>>
>> Let's move the code and clean it up a bit along the way.
>>
>> Signed-off-by: David Hildenbrand (Red Hat) <david@kernel.org>
>> ---
>>    MAINTAINERS     |  1 -
>>    mm/internal.h   | 18 -------------
>>    mm/memory.c     | 70 ++++++++++++++++++++++++++++++++++++++++++-----
>>    mm/pt_reclaim.c | 72 -------------------------------------------------
>>    4 files changed, 64 insertions(+), 97 deletions(-)
>>    delete mode 100644 mm/pt_reclaim.c
> 
> Make sense, and LGTM. The reason it was placed in mm/pt_reclaim.c before
> was because there would be other paths calling these functions in the
> future. However, it can be separated out or put into a header file when
> there are actually such callers.

Most relevant zapping better happens in memory.c :)

There is, of course, zapping due to RMAP unmap, but that mostly targets 
individual PTEs, and not a complete pte table.

Likely, if ever required, we should expose a proper zapping interface 
from memory.c to other users, assuming the existing one is not suitable.

> 
> would you be willing to send out an official patch?

Yes, I can send one out, thanks.

-- 
Cheers

David

Re: [PATCH v3 7/7] mm: make PT_RECLAIM depends on MMU_GATHER_RCU_TABLE_FREE

[David Hildenbrand (Red Hat)]

On 12/17/25 10:45, Qi Zheng wrote:
> From: Qi Zheng <zhengqi.arch@bytedance.com>
> 
> The PT_RECLAIM can work on all architectures that support
> MMU_GATHER_RCU_TABLE_FREE, so make PT_RECLAIM depends on
> MMU_GATHER_RCU_TABLE_FREE.
> 
> BTW, change PT_RECLAIM to be enabled by default, since nobody should want
> to turn it off.

Right, and if there is ever a need to, I wonder whether that should be a 
boottime/runtime toggle instead.

So far we haven't heard of any relevant runtime overheads that causes 
problems.

> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> ---
>   arch/x86/Kconfig | 1 -
>   mm/Kconfig       | 9 ++-------
>   2 files changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 80527299f859a..0d22da56a71b0 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -331,7 +331,6 @@ config X86
>   	select FUNCTION_ALIGNMENT_4B
>   	imply IMA_SECURE_AND_OR_TRUSTED_BOOT    if EFI
>   	select HAVE_DYNAMIC_FTRACE_NO_PATCHABLE
> -	select ARCH_SUPPORTS_PT_RECLAIM		if X86_64
>   	select ARCH_SUPPORTS_SCHED_SMT		if SMP
>   	select SCHED_SMT			if SMP
>   	select ARCH_SUPPORTS_SCHED_CLUSTER	if SMP
> diff --git a/mm/Kconfig b/mm/Kconfig
> index bd0ea5454af82..fc00b429b7129 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -1447,14 +1447,9 @@ config ARCH_HAS_USER_SHADOW_STACK
>   	  The architecture has hardware support for userspace shadow call
>             stacks (eg, x86 CET, arm64 GCS or RISC-V Zicfiss).
>   
> -config ARCH_SUPPORTS_PT_RECLAIM
> -	def_bool n
> -
>   config PT_RECLAIM
> -	bool "reclaim empty user page table pages"
> -	default y
> -	depends on ARCH_SUPPORTS_PT_RECLAIM && MMU && SMP
> -	select MMU_GATHER_RCU_TABLE_FREE
> +	def_bool y
> +	depends on MMU_GATHER_RCU_TABLE_FREE
>   	help
>   	  Try to reclaim empty user page table pages in paths other than munmap
>   	  and exit_mmap path.


Nothing jumped at me. Hopefully we're not missing something important :)

Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>

-- 
Cheers

David

Re: [PATCH v3 7/7] mm: make PT_RECLAIM depends on MMU_GATHER_RCU_TABLE_FREE

[Andreas Larsson]

On 2025-12-17 10:45, Qi Zheng wrote:
> From: Qi Zheng <zhengqi.arch@bytedance.com>
> 
> The PT_RECLAIM can work on all architectures that support
> MMU_GATHER_RCU_TABLE_FREE, so make PT_RECLAIM depends on
> MMU_GATHER_RCU_TABLE_FREE.
> 
> BTW, change PT_RECLAIM to be enabled by default, since nobody should want
> to turn it off.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> ---
>  arch/x86/Kconfig | 1 -
>  mm/Kconfig       | 9 ++-------
>  2 files changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 80527299f859a..0d22da56a71b0 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -331,7 +331,6 @@ config X86
>  	select FUNCTION_ALIGNMENT_4B
>  	imply IMA_SECURE_AND_OR_TRUSTED_BOOT    if EFI
>  	select HAVE_DYNAMIC_FTRACE_NO_PATCHABLE
> -	select ARCH_SUPPORTS_PT_RECLAIM		if X86_64
>  	select ARCH_SUPPORTS_SCHED_SMT		if SMP
>  	select SCHED_SMT			if SMP
>  	select ARCH_SUPPORTS_SCHED_CLUSTER	if SMP
> diff --git a/mm/Kconfig b/mm/Kconfig
> index bd0ea5454af82..fc00b429b7129 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -1447,14 +1447,9 @@ config ARCH_HAS_USER_SHADOW_STACK
>  	  The architecture has hardware support for userspace shadow call
>            stacks (eg, x86 CET, arm64 GCS or RISC-V Zicfiss).
>  
> -config ARCH_SUPPORTS_PT_RECLAIM
> -	def_bool n
> -
>  config PT_RECLAIM
> -	bool "reclaim empty user page table pages"
> -	default y
> -	depends on ARCH_SUPPORTS_PT_RECLAIM && MMU && SMP
> -	select MMU_GATHER_RCU_TABLE_FREE
> +	def_bool y
> +	depends on MMU_GATHER_RCU_TABLE_FREE
>  	help
>  	  Try to reclaim empty user page table pages in paths other than munmap
>  	  and exit_mmap path.

Hi,

This patch unfortunately results in a WARN_ON_ONCE and unaligned
accesses on sparc64:

$ stress-ng --mmaphuge 20 -t 60
stress-ng: info:  [559] setting to a 1 min run per stressor
stress-ng: info:  [559] dispatching hogs: 20 mmaphuge
[  560.592569] ------------[ cut here ]------------
[  560.592663] WARNING: kernel/rcu/tree.c:3098 at __call_rcu_common.constprop.0+0x200/0x760, CPU#4: stress-ng-mmaph/568
[  560.592777] CPU: 4 UID: 1000 PID: 568 Comm: stress-ng-mmaph Not tainted 6.19.0-rc5-00127-g62fc9f6ccb97 #8 VOLUNTARY
[  560.592805] Call Trace:
[  560.592812] [<00000000004368b8>] dump_stack+0x8/0x60
[  560.592844] [<0000000000482a60>] __warn+0xe0/0x140
[  560.592878] [<0000000000482b64>] warn_slowpath_fmt+0xa4/0x120
[  560.592901] [<0000000000526a40>] __call_rcu_common.constprop.0+0x200/0x760
[  560.592931] [<0000000000526fd0>] call_rcu+0x10/0x20
[  560.592954] [<0000000000730838>] tlb_remove_table+0x98/0xc0
[  560.592986] [<000000000071bec4>] free_pgd_range+0x224/0x4c0
[  560.593021] [<000000000071c35c>] free_pgtables+0x1fc/0x240
[  560.593042] [<000000000074a6f0>] vms_clear_ptes+0x110/0x140
[  560.593068] [<000000000074c3dc>] vms_complete_munmap_vmas+0x5c/0x280
[  560.593094] [<000000000074de5c>] do_vmi_align_munmap+0x1dc/0x260
[  560.593117] [<000000000074df80>] do_vmi_munmap+0xa0/0x140
[  560.593142] [<000000000074fb2c>] __vm_munmap+0x8c/0x160
[  560.593168] [<000000000072cfd4>] vm_munmap+0x14/0x40
[  560.593190] [<00000000004402a8>] sys_64_munmap+0x88/0xa0
[  560.593221] [<0000000000406274>] linux_sparc_syscall+0x34/0x44
[  560.593274] ---[ end trace 0000000000000000 ]---
[  560.593960] log_unaligned: 209 callbacks suppressed
[  560.593979] Kernel unaligned access at TPC[526a4c] __call_rcu_common.constprop.0+0x20c/0x760
[  560.594121] Kernel unaligned access at TPC[526864] __call_rcu_common.constprop.0+0x24/0x760
[  560.594198] Kernel unaligned access at TPC[52b3c4] rcu_segcblist_enqueue+0x24/0x40
[  560.594275] Kernel unaligned access at TPC[526860] __call_rcu_common.constprop.0+0x20/0x760
[  560.594360] Kernel unaligned access at TPC[526864] __call_rcu_common.constprop.0+0x24/0x760
[  567.054127] log_unaligned: 1105 callbacks suppressed
[  567.054167] Kernel unaligned access at TPC[526860] __call_rcu_common.constprop.0+0x20/0x760
[  567.054331] Kernel unaligned access at TPC[526864] __call_rcu_common.constprop.0+0x24/0x760
[  567.054410] Kernel unaligned access at TPC[52b3c4] rcu_segcblist_enqueue+0x24/0x40
...

I bisected to this one on mm-unstable from approximately 2026-01-12.

The warning is from 

	/* Misaligned rcu_head! */
	WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));

in __call_rcu_common() and the unaligned accesses follows from there.

Regards,
Andreas

Re: [PATCH v3 7/7] mm: make PT_RECLAIM depends on MMU_GATHER_RCU_TABLE_FREE

[Qi Zheng]

On 1/23/26 11:15 PM, Andreas Larsson wrote:
> On 2025-12-17 10:45, Qi Zheng wrote:
>> From: Qi Zheng <zhengqi.arch@bytedance.com>
>>
>> The PT_RECLAIM can work on all architectures that support
>> MMU_GATHER_RCU_TABLE_FREE, so make PT_RECLAIM depends on
>> MMU_GATHER_RCU_TABLE_FREE.
>>
>> BTW, change PT_RECLAIM to be enabled by default, since nobody should want
>> to turn it off.
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>> ---
>>   arch/x86/Kconfig | 1 -
>>   mm/Kconfig       | 9 ++-------
>>   2 files changed, 2 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index 80527299f859a..0d22da56a71b0 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -331,7 +331,6 @@ config X86
>>   	select FUNCTION_ALIGNMENT_4B
>>   	imply IMA_SECURE_AND_OR_TRUSTED_BOOT    if EFI
>>   	select HAVE_DYNAMIC_FTRACE_NO_PATCHABLE
>> -	select ARCH_SUPPORTS_PT_RECLAIM		if X86_64
>>   	select ARCH_SUPPORTS_SCHED_SMT		if SMP
>>   	select SCHED_SMT			if SMP
>>   	select ARCH_SUPPORTS_SCHED_CLUSTER	if SMP
>> diff --git a/mm/Kconfig b/mm/Kconfig
>> index bd0ea5454af82..fc00b429b7129 100644
>> --- a/mm/Kconfig
>> +++ b/mm/Kconfig
>> @@ -1447,14 +1447,9 @@ config ARCH_HAS_USER_SHADOW_STACK
>>   	  The architecture has hardware support for userspace shadow call
>>             stacks (eg, x86 CET, arm64 GCS or RISC-V Zicfiss).
>>   
>> -config ARCH_SUPPORTS_PT_RECLAIM
>> -	def_bool n
>> -
>>   config PT_RECLAIM
>> -	bool "reclaim empty user page table pages"
>> -	default y
>> -	depends on ARCH_SUPPORTS_PT_RECLAIM && MMU && SMP
>> -	select MMU_GATHER_RCU_TABLE_FREE
>> +	def_bool y
>> +	depends on MMU_GATHER_RCU_TABLE_FREE
>>   	help
>>   	  Try to reclaim empty user page table pages in paths other than munmap
>>   	  and exit_mmap path.
> 
> Hi,
> 
> This patch unfortunately results in a WARN_ON_ONCE and unaligned
> accesses on sparc64:
> 
> $ stress-ng --mmaphuge 20 -t 60
> stress-ng: info:  [559] setting to a 1 min run per stressor
> stress-ng: info:  [559] dispatching hogs: 20 mmaphuge
> [  560.592569] ------------[ cut here ]------------
> [  560.592663] WARNING: kernel/rcu/tree.c:3098 at __call_rcu_common.constprop.0+0x200/0x760, CPU#4: stress-ng-mmaph/568
> [  560.592777] CPU: 4 UID: 1000 PID: 568 Comm: stress-ng-mmaph Not tainted 6.19.0-rc5-00127-g62fc9f6ccb97 #8 VOLUNTARY
> [  560.592805] Call Trace:
> [  560.592812] [<00000000004368b8>] dump_stack+0x8/0x60
> [  560.592844] [<0000000000482a60>] __warn+0xe0/0x140
> [  560.592878] [<0000000000482b64>] warn_slowpath_fmt+0xa4/0x120
> [  560.592901] [<0000000000526a40>] __call_rcu_common.constprop.0+0x200/0x760
> [  560.592931] [<0000000000526fd0>] call_rcu+0x10/0x20
> [  560.592954] [<0000000000730838>] tlb_remove_table+0x98/0xc0
> [  560.592986] [<000000000071bec4>] free_pgd_range+0x224/0x4c0
> [  560.593021] [<000000000071c35c>] free_pgtables+0x1fc/0x240
> [  560.593042] [<000000000074a6f0>] vms_clear_ptes+0x110/0x140
> [  560.593068] [<000000000074c3dc>] vms_complete_munmap_vmas+0x5c/0x280
> [  560.593094] [<000000000074de5c>] do_vmi_align_munmap+0x1dc/0x260
> [  560.593117] [<000000000074df80>] do_vmi_munmap+0xa0/0x140
> [  560.593142] [<000000000074fb2c>] __vm_munmap+0x8c/0x160
> [  560.593168] [<000000000072cfd4>] vm_munmap+0x14/0x40
> [  560.593190] [<00000000004402a8>] sys_64_munmap+0x88/0xa0
> [  560.593221] [<0000000000406274>] linux_sparc_syscall+0x34/0x44
> [  560.593274] ---[ end trace 0000000000000000 ]---
> [  560.593960] log_unaligned: 209 callbacks suppressed
> [  560.593979] Kernel unaligned access at TPC[526a4c] __call_rcu_common.constprop.0+0x20c/0x760
> [  560.594121] Kernel unaligned access at TPC[526864] __call_rcu_common.constprop.0+0x24/0x760
> [  560.594198] Kernel unaligned access at TPC[52b3c4] rcu_segcblist_enqueue+0x24/0x40
> [  560.594275] Kernel unaligned access at TPC[526860] __call_rcu_common.constprop.0+0x20/0x760
> [  560.594360] Kernel unaligned access at TPC[526864] __call_rcu_common.constprop.0+0x24/0x760
> [  567.054127] log_unaligned: 1105 callbacks suppressed
> [  567.054167] Kernel unaligned access at TPC[526860] __call_rcu_common.constprop.0+0x20/0x760
> [  567.054331] Kernel unaligned access at TPC[526864] __call_rcu_common.constprop.0+0x24/0x760
> [  567.054410] Kernel unaligned access at TPC[52b3c4] rcu_segcblist_enqueue+0x24/0x40

Thanks for your report!

On sparc64, pmd and pud levels are not of struct page:

__pmd_free_tlb/__pud_free_tlb
--> pgtable_free_tlb(tlb, pud/pmd, false). <=== is_page == false
     --> tlb_remove_table

So in __tlb_remove_table_one(), the table cannot be treated as
ptdesc because it does not have an pt_rcu_head member.

Hi David, it seems we still need to keep ARCH_SUPPORTS_PT_RECLAIM?

Thanks,
Qi

> ...
> 
> I bisected to this one on mm-unstable from approximately 2026-01-12.
> 
> The warning is from
> 
> 	/* Misaligned rcu_head! */
> 	WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
> 
> in __call_rcu_common() and the unaligned accesses follows from there.
> 
> Regards,
> Andreas
> 

Re: [PATCH v3 7/7] mm: make PT_RECLAIM depends on MMU_GATHER_RCU_TABLE_FREE

[David Hildenbrand (Red Hat)]

On 1/26/26 07:59, Qi Zheng wrote:
> 
> 
> On 1/23/26 11:15 PM, Andreas Larsson wrote:
>> On 2025-12-17 10:45, Qi Zheng wrote:
>>> From: Qi Zheng <zhengqi.arch@bytedance.com>
>>>
>>> The PT_RECLAIM can work on all architectures that support
>>> MMU_GATHER_RCU_TABLE_FREE, so make PT_RECLAIM depends on
>>> MMU_GATHER_RCU_TABLE_FREE.
>>>
>>> BTW, change PT_RECLAIM to be enabled by default, since nobody should want
>>> to turn it off.
>>>
>>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>>> ---
>>>    arch/x86/Kconfig | 1 -
>>>    mm/Kconfig       | 9 ++-------
>>>    2 files changed, 2 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>>> index 80527299f859a..0d22da56a71b0 100644
>>> --- a/arch/x86/Kconfig
>>> +++ b/arch/x86/Kconfig
>>> @@ -331,7 +331,6 @@ config X86
>>>    	select FUNCTION_ALIGNMENT_4B
>>>    	imply IMA_SECURE_AND_OR_TRUSTED_BOOT    if EFI
>>>    	select HAVE_DYNAMIC_FTRACE_NO_PATCHABLE
>>> -	select ARCH_SUPPORTS_PT_RECLAIM		if X86_64
>>>    	select ARCH_SUPPORTS_SCHED_SMT		if SMP
>>>    	select SCHED_SMT			if SMP
>>>    	select ARCH_SUPPORTS_SCHED_CLUSTER	if SMP
>>> diff --git a/mm/Kconfig b/mm/Kconfig
>>> index bd0ea5454af82..fc00b429b7129 100644
>>> --- a/mm/Kconfig
>>> +++ b/mm/Kconfig
>>> @@ -1447,14 +1447,9 @@ config ARCH_HAS_USER_SHADOW_STACK
>>>    	  The architecture has hardware support for userspace shadow call
>>>              stacks (eg, x86 CET, arm64 GCS or RISC-V Zicfiss).
>>>    
>>> -config ARCH_SUPPORTS_PT_RECLAIM
>>> -	def_bool n
>>> -
>>>    config PT_RECLAIM
>>> -	bool "reclaim empty user page table pages"
>>> -	default y
>>> -	depends on ARCH_SUPPORTS_PT_RECLAIM && MMU && SMP
>>> -	select MMU_GATHER_RCU_TABLE_FREE
>>> +	def_bool y
>>> +	depends on MMU_GATHER_RCU_TABLE_FREE
>>>    	help
>>>    	  Try to reclaim empty user page table pages in paths other than munmap
>>>    	  and exit_mmap path.
>>
>> Hi,
>>
>> This patch unfortunately results in a WARN_ON_ONCE and unaligned
>> accesses on sparc64:
>>
>> $ stress-ng --mmaphuge 20 -t 60
>> stress-ng: info:  [559] setting to a 1 min run per stressor
>> stress-ng: info:  [559] dispatching hogs: 20 mmaphuge
>> [  560.592569] ------------[ cut here ]------------
>> [  560.592663] WARNING: kernel/rcu/tree.c:3098 at __call_rcu_common.constprop.0+0x200/0x760, CPU#4: stress-ng-mmaph/568
>> [  560.592777] CPU: 4 UID: 1000 PID: 568 Comm: stress-ng-mmaph Not tainted 6.19.0-rc5-00127-g62fc9f6ccb97 #8 VOLUNTARY
>> [  560.592805] Call Trace:
>> [  560.592812] [<00000000004368b8>] dump_stack+0x8/0x60
>> [  560.592844] [<0000000000482a60>] __warn+0xe0/0x140
>> [  560.592878] [<0000000000482b64>] warn_slowpath_fmt+0xa4/0x120
>> [  560.592901] [<0000000000526a40>] __call_rcu_common.constprop.0+0x200/0x760
>> [  560.592931] [<0000000000526fd0>] call_rcu+0x10/0x20
>> [  560.592954] [<0000000000730838>] tlb_remove_table+0x98/0xc0
>> [  560.592986] [<000000000071bec4>] free_pgd_range+0x224/0x4c0
>> [  560.593021] [<000000000071c35c>] free_pgtables+0x1fc/0x240
>> [  560.593042] [<000000000074a6f0>] vms_clear_ptes+0x110/0x140
>> [  560.593068] [<000000000074c3dc>] vms_complete_munmap_vmas+0x5c/0x280
>> [  560.593094] [<000000000074de5c>] do_vmi_align_munmap+0x1dc/0x260
>> [  560.593117] [<000000000074df80>] do_vmi_munmap+0xa0/0x140
>> [  560.593142] [<000000000074fb2c>] __vm_munmap+0x8c/0x160
>> [  560.593168] [<000000000072cfd4>] vm_munmap+0x14/0x40
>> [  560.593190] [<00000000004402a8>] sys_64_munmap+0x88/0xa0
>> [  560.593221] [<0000000000406274>] linux_sparc_syscall+0x34/0x44
>> [  560.593274] ---[ end trace 0000000000000000 ]---
>> [  560.593960] log_unaligned: 209 callbacks suppressed
>> [  560.593979] Kernel unaligned access at TPC[526a4c] __call_rcu_common.constprop.0+0x20c/0x760
>> [  560.594121] Kernel unaligned access at TPC[526864] __call_rcu_common.constprop.0+0x24/0x760
>> [  560.594198] Kernel unaligned access at TPC[52b3c4] rcu_segcblist_enqueue+0x24/0x40
>> [  560.594275] Kernel unaligned access at TPC[526860] __call_rcu_common.constprop.0+0x20/0x760
>> [  560.594360] Kernel unaligned access at TPC[526864] __call_rcu_common.constprop.0+0x24/0x760
>> [  567.054127] log_unaligned: 1105 callbacks suppressed
>> [  567.054167] Kernel unaligned access at TPC[526860] __call_rcu_common.constprop.0+0x20/0x760
>> [  567.054331] Kernel unaligned access at TPC[526864] __call_rcu_common.constprop.0+0x24/0x760
>> [  567.054410] Kernel unaligned access at TPC[52b3c4] rcu_segcblist_enqueue+0x24/0x40
> 
> Thanks for your report!
> 
> On sparc64, pmd and pud levels are not of struct page:

Can you elaborate, I don't understand what you mean :)

Is it also a problem on architectures like s390x and ppc, where we 
squeeze multiple page tables into a physical pages?

> 
> __pmd_free_tlb/__pud_free_tlb
> --> pgtable_free_tlb(tlb, pud/pmd, false). <=== is_page == false
>       --> tlb_remove_table
> 
> So in __tlb_remove_table_one(), the table cannot be treated as
> ptdesc because it does not have an pt_rcu_head member.
> 
> Hi David, it seems we still need to keep ARCH_SUPPORTS_PT_RECLAIM?

Or we invert it and only disable it for the known-problematic architectures?

-- 
Cheers

David

Re: [PATCH v3 7/7] mm: make PT_RECLAIM depends on MMU_GATHER_RCU_TABLE_FREE

[Qi Zheng]

On 1/27/26 7:29 PM, David Hildenbrand (Red Hat) wrote:
> On 1/26/26 07:59, Qi Zheng wrote:
>>
>>
>> On 1/23/26 11:15 PM, Andreas Larsson wrote:
>>> On 2025-12-17 10:45, Qi Zheng wrote:
>>>> From: Qi Zheng <zhengqi.arch@bytedance.com>
>>>>
>>>> The PT_RECLAIM can work on all architectures that support
>>>> MMU_GATHER_RCU_TABLE_FREE, so make PT_RECLAIM depends on
>>>> MMU_GATHER_RCU_TABLE_FREE.
>>>>
>>>> BTW, change PT_RECLAIM to be enabled by default, since nobody should 
>>>> want
>>>> to turn it off.
>>>>
>>>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>>>> ---
>>>>    arch/x86/Kconfig | 1 -
>>>>    mm/Kconfig       | 9 ++-------
>>>>    2 files changed, 2 insertions(+), 8 deletions(-)
>>>>
>>>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>>>> index 80527299f859a..0d22da56a71b0 100644
>>>> --- a/arch/x86/Kconfig
>>>> +++ b/arch/x86/Kconfig
>>>> @@ -331,7 +331,6 @@ config X86
>>>>        select FUNCTION_ALIGNMENT_4B
>>>>        imply IMA_SECURE_AND_OR_TRUSTED_BOOT    if EFI
>>>>        select HAVE_DYNAMIC_FTRACE_NO_PATCHABLE
>>>> -    select ARCH_SUPPORTS_PT_RECLAIM        if X86_64
>>>>        select ARCH_SUPPORTS_SCHED_SMT        if SMP
>>>>        select SCHED_SMT            if SMP
>>>>        select ARCH_SUPPORTS_SCHED_CLUSTER    if SMP
>>>> diff --git a/mm/Kconfig b/mm/Kconfig
>>>> index bd0ea5454af82..fc00b429b7129 100644
>>>> --- a/mm/Kconfig
>>>> +++ b/mm/Kconfig
>>>> @@ -1447,14 +1447,9 @@ config ARCH_HAS_USER_SHADOW_STACK
>>>>          The architecture has hardware support for userspace shadow 
>>>> call
>>>>              stacks (eg, x86 CET, arm64 GCS or RISC-V Zicfiss).
>>>> -config ARCH_SUPPORTS_PT_RECLAIM
>>>> -    def_bool n
>>>> -
>>>>    config PT_RECLAIM
>>>> -    bool "reclaim empty user page table pages"
>>>> -    default y
>>>> -    depends on ARCH_SUPPORTS_PT_RECLAIM && MMU && SMP
>>>> -    select MMU_GATHER_RCU_TABLE_FREE
>>>> +    def_bool y
>>>> +    depends on MMU_GATHER_RCU_TABLE_FREE
>>>>        help
>>>>          Try to reclaim empty user page table pages in paths other 
>>>> than munmap
>>>>          and exit_mmap path.
>>>
>>> Hi,
>>>
>>> This patch unfortunately results in a WARN_ON_ONCE and unaligned
>>> accesses on sparc64:
>>>
>>> $ stress-ng --mmaphuge 20 -t 60
>>> stress-ng: info:  [559] setting to a 1 min run per stressor
>>> stress-ng: info:  [559] dispatching hogs: 20 mmaphuge
>>> [  560.592569] ------------[ cut here ]------------
>>> [  560.592663] WARNING: kernel/rcu/tree.c:3098 at 
>>> __call_rcu_common.constprop.0+0x200/0x760, CPU#4: stress-ng-mmaph/568
>>> [  560.592777] CPU: 4 UID: 1000 PID: 568 Comm: stress-ng-mmaph Not 
>>> tainted 6.19.0-rc5-00127-g62fc9f6ccb97 #8 VOLUNTARY
>>> [  560.592805] Call Trace:
>>> [  560.592812] [<00000000004368b8>] dump_stack+0x8/0x60
>>> [  560.592844] [<0000000000482a60>] __warn+0xe0/0x140
>>> [  560.592878] [<0000000000482b64>] warn_slowpath_fmt+0xa4/0x120
>>> [  560.592901] [<0000000000526a40>] 
>>> __call_rcu_common.constprop.0+0x200/0x760
>>> [  560.592931] [<0000000000526fd0>] call_rcu+0x10/0x20
>>> [  560.592954] [<0000000000730838>] tlb_remove_table+0x98/0xc0
>>> [  560.592986] [<000000000071bec4>] free_pgd_range+0x224/0x4c0
>>> [  560.593021] [<000000000071c35c>] free_pgtables+0x1fc/0x240
>>> [  560.593042] [<000000000074a6f0>] vms_clear_ptes+0x110/0x140
>>> [  560.593068] [<000000000074c3dc>] vms_complete_munmap_vmas+0x5c/0x280
>>> [  560.593094] [<000000000074de5c>] do_vmi_align_munmap+0x1dc/0x260
>>> [  560.593117] [<000000000074df80>] do_vmi_munmap+0xa0/0x140
>>> [  560.593142] [<000000000074fb2c>] __vm_munmap+0x8c/0x160
>>> [  560.593168] [<000000000072cfd4>] vm_munmap+0x14/0x40
>>> [  560.593190] [<00000000004402a8>] sys_64_munmap+0x88/0xa0
>>> [  560.593221] [<0000000000406274>] linux_sparc_syscall+0x34/0x44
>>> [  560.593274] ---[ end trace 0000000000000000 ]---
>>> [  560.593960] log_unaligned: 209 callbacks suppressed
>>> [  560.593979] Kernel unaligned access at TPC[526a4c] 
>>> __call_rcu_common.constprop.0+0x20c/0x760
>>> [  560.594121] Kernel unaligned access at TPC[526864] 
>>> __call_rcu_common.constprop.0+0x24/0x760
>>> [  560.594198] Kernel unaligned access at TPC[52b3c4] 
>>> rcu_segcblist_enqueue+0x24/0x40
>>> [  560.594275] Kernel unaligned access at TPC[526860] 
>>> __call_rcu_common.constprop.0+0x20/0x760
>>> [  560.594360] Kernel unaligned access at TPC[526864] 
>>> __call_rcu_common.constprop.0+0x24/0x760
>>> [  567.054127] log_unaligned: 1105 callbacks suppressed
>>> [  567.054167] Kernel unaligned access at TPC[526860] 
>>> __call_rcu_common.constprop.0+0x20/0x760
>>> [  567.054331] Kernel unaligned access at TPC[526864] 
>>> __call_rcu_common.constprop.0+0x24/0x760
>>> [  567.054410] Kernel unaligned access at TPC[52b3c4] 
>>> rcu_segcblist_enqueue+0x24/0x40
>>
>> Thanks for your report!
>>
>> On sparc64, pmd and pud levels are not of struct page:
> 
> Can you elaborate, I don't understand what you mean :)

On sparc64:

static inline void pgtable_free_tlb(struct mmu_gather *tlb, void *table, 
bool is_page)
{
	unsigned long pgf = (unsigned long)table;
	if (is_page)
		pgf |= 0x1UL;
	tlb_remove_table(tlb, (void *)pgf);
}

static inline void __tlb_remove_table(void *_table)
{
	void *table = (void *)((unsigned long)_table & ~0x1UL);
	bool is_page = false;

	if ((unsigned long)_table & 0x1UL)
		is_page = true;
	pgtable_free(table, is_page);
}

void pgtable_free(void *table, bool is_page)
{
	if (is_page)
		__pte_free(table);
	else
		kmem_cache_free(pgtable_cache, table);
}

For pmd and pud levels, is_page is false, so we can not do the
following in __tlb_remove_table_one().

```
	ptdesc = table;
	call_rcu(&ptdesc->pt_rcu_head, __tlb_remove_table_one_rcu);
```

> 
> Is it also a problem on architectures like s390x and ppc, where we 
> squeeze multiple page tables into a physical pages?

For ppc, it's the same as for sparc64.

For s390x, it supports MMU_GATHER_RCU_TABLE_FREE and define its own
pxx_free_tlb(), but these all call tlb_remove_ptdesc(), so there is no
problem.

> 
>>
>> __pmd_free_tlb/__pud_free_tlb
>> --> pgtable_free_tlb(tlb, pud/pmd, false). <=== is_page == false
>>       --> tlb_remove_table
>>
>> So in __tlb_remove_table_one(), the table cannot be treated as
>> ptdesc because it does not have an pt_rcu_head member.
>>
>> Hi David, it seems we still need to keep ARCH_SUPPORTS_PT_RECLAIM?
> 
> Or we invert it and only disable it for the known-problematic 
> architectures?

Yes, the problem lies with those architectures that support
MMU_GATHER_RCU_TABLE_FREE and define their own _tlb_remove_table().

So my plan is as follows:

1. convert __HAVE_ARCH_TLB_REMOVE_TABLE to 
CONFIG_HAVE_ARCH_TLB_REMOVE_TABLE config
2. make PT_RECLAIM depends on MMU_GATHER_RCU_TABLE_FREE && 
!HAVE_ARCH_TLB_REMOVE_TABLE

I'll send v4 soon.

Thanks,
Qi

>