linux-kernel - Re: [PATCH 3/7] loongarch: mm: enable MMU_GATHER_RCU_TABLE

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Message-ID: <fc08c1a8-f469-43f1-93c0-7fcd2b1c477c@linux.dev>
Date: Fri, 14 Nov 2025 23:55:11 +0800
From: Qi Zheng <qi.zheng@...ux.dev>
To: Huacai Chen <chenhuacai@...nel.org>
Cc: 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, 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,
 Qi Zheng <zhengqi.arch@...edance.com>, WANG Xuerui <kernel@...0n.name>
Subject: Re: [PATCH 3/7] loongarch: mm: enable MMU_GATHER_RCU_TABLE_FREE

Hi Huacai,

On 11/14/25 10:17 PM, Huacai Chen wrote:
> Hi, Qi Zheng,
> 
> We usually use LoongArch rather than loongarch, but if you want to
> keep consistency for all patches, just do it.

OK, will change to use LoongArch.

> 
> On Fri, Nov 14, 2025 at 7:13 PM Qi Zheng <qi.zheng@...ux.dev> 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: Huacai Chen <chenhuacai@...nel.org>
>> Cc: WANG Xuerui <kernel@...0n.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.

OK, will do.

> 
>>
>>   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.

will do.

> 
>>
>>   #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.

Got it, will convert them all to the one-line type.

Thanks,
Qi

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