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

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Message-ID: <6e6d8390-1f9e-40cf-949d-168160fa9a15@linux.dev>
Date: Wed, 19 Nov 2025 20:15:58 +0800
From: Qi Zheng <qi.zheng@...ux.dev>
To: "David Hildenbrand (Red Hat)" <david@...nel.org>, will@...nel.org,
 aneesh.kumar@...nel.org, npiggin@...il.com, peterz@...radead.org,
 dev.jain@....com, akpm@...ux-foundation.org, ioworker0@...il.com,
 linmag7@...il.com
Cc: linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, linux-alpha@...r.kernel.org, loongarch@...ts.linux.dev,
 linux-mips@...r.kernel.org, linux-parisc@...r.kernel.org,
 linux-um@...ts.infradead.org, Qi Zheng <zhengqi.arch@...edance.com>
Subject: Re: [PATCH v2 7/7] mm: enable PT_RECLAIM on all 64-bit architectures



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@...edance.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@...edance.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.

> 
>