linux-kernel - Re: [PATCH v3 1/2] mm: use update_mmu

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Message-ID: <1a679784-542f-1ab7-7ba8-3d560c264479@bytedance.com>
Date:   Sat, 1 Oct 2022 07:09:50 +0800
From:   Qi Zheng <zhengqi.arch@...edance.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     David Hildenbrand <david@...hat.com>, maobibo@...ngson.cn,
        chenhuacai@...ngson.cn, songmuchun@...edance.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        loongarch@...ts.linux.dev, chris@...kel.net, jcmvbkbc@...il.com
Subject: Re: [PATCH v3 1/2] mm: use update_mmu_tlb() on the second thread



On 2022/10/1 06:31, Andrew Morton wrote:
> On Fri, 30 Sep 2022 10:44:21 +0200 David Hildenbrand <david@...hat.com> wrote:
> 
>>> Oh, this is better. Hi Andrew, do I need to resend the v4?
>>>
>>
>> I assume he can squash it, most probably no need to resend. :)
> 
> 
> From: Qi Zheng <zhengqi.arch@...edance.com>
> Subject: mm: use update_mmu_tlb() on the second thread
> Date: Thu, 29 Sep 2022 19:23:17 +0800
> 
> As message in commit 7df676974359 ("mm/memory.c: Update local TLB if PTE
> entry exists") said, we should update local TLB only on the second thread.
> So in the do_anonymous_page() here, we should use update_mmu_tlb()
> instead of update_mmu_cache() on the second thread.
> 
> As David pointed out, this is a performance improvement, not a
> correctness fix.
> 
> Link: https://lkml.kernel.org/r/20220929112318.32393-2-zhengqi.arch@bytedance.com
> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
> Reviewed-by: Muchun Song <songmuchun@...edance.com>
> Acked-by: David Hildenbrand <david@...hat.com>
> Cc: Bibo Mao <maobibo@...ngson.cn>
> Cc: Chris Zankel <chris@...kel.net>
> Cc: Huacai Chen <chenhuacai@...ngson.cn>
> Cc: Max Filippov <jcmvbkbc@...il.com>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> ---
> 
>   mm/memory.c |    2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/mm/memory.c~mm-use-update_mmu_tlb-on-the-second-thread
> +++ a/mm/memory.c
> @@ -4136,7 +4136,7 @@ static vm_fault_t do_anonymous_page(stru
>   	vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address,
>   			&vmf->ptl);
>   	if (!pte_none(*vmf->pte)) {
> -		update_mmu_cache(vma, vmf->address, vmf->pte);
> +		update_mmu_tlb(vma, vmf->address, vmf->pte);
>   		goto release;
>   	}
>   
> _

Thank you very much! :)

> 

-- 
Thanks,
Qi