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[PATCH v2 7/7] mm: enable PT_RECLAIM on all 64-bit architectures

Qi Zheng posted 7 patches 1 week, 5 days ago
[PATCH v2 7/7] mm: enable PT_RECLAIM on all 64-bit architectures
Posted by Qi Zheng 1 week, 5 days ago 
From: Qi Zheng <zhengqi.arch@bytedance.com>

Now, the MMU_GATHER_RCU_TABLE_FREE is enabled on all 64-bit architectures,
so make PT_RECLAIM depend on 64BIT, thereby enabling PT_RECLAIM on all
64-bit architectures.

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 eac2e86056902..96bff81fd4787 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -330,7 +330,6 @@ 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 d548976d0e0ad..94eec5c0cad96 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -1448,14 +1448,9 @@ 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 64BIT
 	help
 	  Try to reclaim empty user page table pages in paths other than munmap
 	  and exit_mmap path.
-- 
2.20.1
Re: [PATCH v2 7/7] mm: enable PT_RECLAIM on all 64-bit architectures
Posted by David Hildenbrand (Red Hat) 1 week, 5 days ago 
On 19.11.25 08:31, Qi Zheng wrote:
> From: Qi Zheng <zhengqi.arch@bytedance.com>
> 
> Now, the MMU_GATHER_RCU_TABLE_FREE is enabled on all 64-bit architectures,
> so make PT_RECLAIM depend on 64BIT, thereby enabling PT_RECLAIM on all
> 64-bit architectures.
> 
> 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 eac2e86056902..96bff81fd4787 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -330,7 +330,6 @@ 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 d548976d0e0ad..94eec5c0cad96 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -1448,14 +1448,9 @@ 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 64BIT

As discussed in the other thread, likely

config PT_RECLAIM
	def_bool y
	depends on MMU_GATHER_RCU_TABLE_FREE && 64BIT

Could be nice, and if possible even dropping the 64BIT limitation as 
well if there is no need to.


-- 
Cheers

David
Re: [PATCH v2 7/7] mm: enable PT_RECLAIM on all 64-bit architectures
Posted by Qi Zheng 1 week, 5 days ago 

On 11/19/25 7:38 PM, David Hildenbrand (Red Hat) wrote:
> On 19.11.25 08:31, Qi Zheng wrote:
>> From: Qi Zheng <zhengqi.arch@bytedance.com>
>>
>> Now, the MMU_GATHER_RCU_TABLE_FREE is enabled on all 64-bit 
>> architectures,
>> so make PT_RECLAIM depend on 64BIT, thereby enabling PT_RECLAIM on all
>> 64-bit architectures.
>>
>> 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 eac2e86056902..96bff81fd4787 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -330,7 +330,6 @@ 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 d548976d0e0ad..94eec5c0cad96 100644
>> --- a/mm/Kconfig
>> +++ b/mm/Kconfig
>> @@ -1448,14 +1448,9 @@ 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 64BIT
> 
> As discussed in the other thread, likely
> 
> config PT_RECLAIM
>      def_bool y
>      depends on MMU_GATHER_RCU_TABLE_FREE && 64BIT
> 
> Could be nice, and if possible even dropping the 64BIT limitation as 
> well if there is no need to.

I think it's ok to drop the 64BIT limitation. There should be some
32-bit architectures that already enable MMU_GATHER_RCU_TABLE_FREE.

> 
>

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