Re: [PATCH 3/7] loongarch: mm: enable MMU_GATHER_RCU_TABLE_FREE

Huacai Chen
2025-11-14T14:18:09Z

Hi, Qi Zheng,

We usually use LoongArch rather than loongarch, but if you want to
keep consistency for all patches, just do it.

On Fri, Nov 14, 2025 at 7:13 PM Qi Zheng <qi.zheng@linux.dev> wrote:
>
> 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 | 6 ++++--
> 2 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> index 5b1116733d881..3bf2f2a9cd647 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -210,6 +210,7 @@ config LOONGARCH
> select USER_STACKTRACE_SUPPORT
> select VDSO_GETRANDOM
> select ZONE_DMA32
> + select MMU_GATHER_RCU_TABLE_FREE
Please use alpha-betical order.

>
> config 32BIT
> bool
> diff --git a/arch/loongarch/include/asm/pgalloc.h b/arch/loongarch/include/asm/pgalloc.h
> index 1c63a9d9a6d35..0539d04bf1525 100644
> --- a/arch/loongarch/include/asm/pgalloc.h
> +++ b/arch/loongarch/include/asm/pgalloc.h
> @@ -79,7 +79,8 @@ 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))
I think we can define it in one line.

>
> #endif
>
> @@ -99,7 +100,8 @@ 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))
The same.

Other patches have the same problem.

Huacai

>
> #endif /* __PAGETABLE_PUD_FOLDED */
>
> --
> 2.20.1
>