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

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Message-ID: <9b55623a-4606-4610-a0fe-55b8cd6b95e7@kernel.org>
Date: Wed, 19 Nov 2025 12:38:46 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: Qi Zheng <qi.zheng@...ux.dev>, 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 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.


-- 
Cheers

David