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

David Hildenbrand (Red Hat)
2026-01-19T10:18:59Z

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