linux-kernel - Re: [PATCH v3 2/2] LoongArch: update local TLB if PTE entry exists

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Message-ID: <1755ade9-9333-4dc2-dd06-eb1f87d6b30d@bytedance.com>
Date:   Thu, 29 Sep 2022 20:10:42 +0800
From:   Qi Zheng <zhengqi.arch@...edance.com>
To:     Huacai Chen <chenhuacai@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     maobibo@...ngson.cn, chenhuacai@...ngson.cn,
        songmuchun@...edance.com, david@...hat.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        loongarch@...ts.linux.dev, chris@...kel.net, jcmvbkbc@...il.com
Subject: Re: [PATCH v3 2/2] LoongArch: update local TLB if PTE entry exists



On 2022/9/29 19:42, Huacai Chen wrote:
> Hi, all,
> 
> Should this patch go via mm tree or loongarch tree? If via mm tree, then

Both are fine for me. Hi Andrew, can you help to apply this patch
series?

> 
> Acked-by: Huacai Chen <chenhuacai@...ngson.cn>

Thanks. :)

> 
> On Thu, Sep 29, 2022 at 7:23 PM Qi Zheng <zhengqi.arch@...edance.com> wrote:
>>
>> Currently, the implementation of update_mmu_tlb() is empty if
>> __HAVE_ARCH_UPDATE_MMU_TLB is not defined. Then if two threads
>> concurrently fault at the same page, the second thread that did
>> not win the race will give up and do nothing. In the LoongArch
>> architecture, this second thread will trigger another fault,
>> and only updates its local TLB.
>>
>> Instead of triggering another fault, it's better to implement
>> update_mmu_tlb() to directly update the local TLB of the second
>> thread. Just do it.
>>
>> Suggested-by: Bibo Mao <maobibo@...ngson.cn>
>> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
>> ---
>>   arch/loongarch/include/asm/pgtable.h | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h
>> index 8ea57e2f0e04..946704bee599 100644
>> --- a/arch/loongarch/include/asm/pgtable.h
>> +++ b/arch/loongarch/include/asm/pgtable.h
>> @@ -412,6 +412,9 @@ static inline void update_mmu_cache(struct vm_area_struct *vma,
>>          __update_tlb(vma, address, ptep);
>>   }
>>
>> +#define __HAVE_ARCH_UPDATE_MMU_TLB
>> +#define update_mmu_tlb update_mmu_cache
>> +
>>   static inline void update_mmu_cache_pmd(struct vm_area_struct *vma,
>>                          unsigned long address, pmd_t *pmdp)
>>   {
>> --
>> 2.20.1
>>
>>

-- 
Thanks,
Qi