linux-kernel - Re: [PATCH 2/7] arc: mm: enable MMU_GATHER_RCU_TABLE

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Message-ID: <5199c367-aabb-43e7-951e-452657dcdddc@linux.dev>
Date: Fri, 14 Nov 2025 19:20:02 +0800
From: Qi Zheng <qi.zheng@...ux.dev>
To: will@...nel.org, aneesh.kumar@...nel.org, npiggin@...il.com,
 peterz@...radead.org, dev.jain@....com, akpm@...ux-foundation.org,
 david@...hat.com, ioworker0@...il.com
Cc: linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, linux-alpha@...r.kernel.org,
 linux-snps-arc@...ts.infradead.org, loongarch@...ts.linux.dev,
 linux-mips@...r.kernel.org, linux-parisc@...r.kernel.org,
 linux-um@...ts.infradead.org, Vineet Gupta <vgupta@...nel.org>
Subject: Re: [PATCH 2/7] arc: mm: enable MMU_GATHER_RCU_TABLE_FREE



On 11/14/25 7:11 PM, Qi Zheng wrote:
> From: Qi Zheng <zhengqi.arch@...edance.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@...edance.com>
> Cc: Vineet Gupta <vgupta@...nel.org>
> ---
>   arch/arc/Kconfig               | 1 +
>   arch/arc/include/asm/pgalloc.h | 9 ++++++---
>   2 files changed, 7 insertions(+), 3 deletions(-)

Strangely, it seems that only ARC does not define CONFIG_64BIT?

Does the ARC architecture support 64-bit? Did I miss something?

> 
> diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
> index f27e6b90428e4..47db93952386d 100644
> --- a/arch/arc/Kconfig
> +++ b/arch/arc/Kconfig
> @@ -54,6 +54,7 @@ config ARC
>   	select HAVE_ARCH_JUMP_LABEL if ISA_ARCV2 && !CPU_ENDIAN_BE32
>   	select TRACE_IRQFLAGS_SUPPORT
>   	select HAVE_EBPF_JIT if ISA_ARCV2
> +	select MMU_GATHER_RCU_TABLE_FREE
>   
>   config LOCKDEP_SUPPORT
>   	def_bool y
> diff --git a/arch/arc/include/asm/pgalloc.h b/arch/arc/include/asm/pgalloc.h
> index dfae070fe8d55..b1c6619435613 100644
> --- a/arch/arc/include/asm/pgalloc.h
> +++ b/arch/arc/include/asm/pgalloc.h
> @@ -72,7 +72,8 @@ static inline void p4d_populate(struct mm_struct *mm, p4d_t *p4dp, pud_t *pudp)
>   	set_p4d(p4dp, __p4d((unsigned long)pudp));
>   }
>   
> -#define __pud_free_tlb(tlb, pmd, addr)  pud_free((tlb)->mm, pmd)
> +#define __pud_free_tlb(tlb, pud, addr)	\
> +	tlb_remove_ptdesc((tlb), virt_to_ptdesc(pud))
>   
>   #endif
>   
> @@ -83,10 +84,12 @@ static inline void pud_populate(struct mm_struct *mm, pud_t *pudp, pmd_t *pmdp)
>   	set_pud(pudp, __pud((unsigned long)pmdp));
>   }
>   
> -#define __pmd_free_tlb(tlb, pmd, addr)  pmd_free((tlb)->mm, pmd)
> +#define __pmd_free_tlb(tlb, pmd, addr)	\
> +	tlb_remove_ptdesc((tlb), virt_to_ptdesc(pmd))
>   
>   #endif
>   
> -#define __pte_free_tlb(tlb, pte, addr)  pte_free((tlb)->mm, pte)
> +#define __pte_free_tlb(tlb, pte, addr)	\
> +	tlb_remove_ptdesc((tlb), page_ptdesc(pte))
>   
>   #endif /* _ASM_ARC_PGALLOC_H */