linux-kernel - Re: [PATCH v2] mm: use update_mmu

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Message-ID: <d4e4a362-fbf2-7eea-e021-16ae7782e06e@bytedance.com>
Date:   Thu, 29 Sep 2022 11:47:13 +0800
From:   Qi Zheng <zhengqi.arch@...edance.com>
To:     maobibo <maobibo@...ngson.cn>,
        David Hildenbrand <david@...hat.com>,
        akpm@...ux-foundation.org, muchun.song@...ux.dev,
        陈华才 <chenhuacai@...ngson.cn>
Cc:     chris@...kel.net, jcmvbkbc@...il.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>
Subject: Re: [PATCH v2] mm: use update_mmu_tlb() on the second thread



On 2022/9/29 11:27, maobibo wrote:
> 在 2022/9/29 11:07, Qi Zheng 写道:
>>
>>
>> On 2022/9/26 22:34, David Hildenbrand wrote:
>>> On 26.09.22 13:56, Qi Zheng wrote:
>>>> 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.
>>>>
>>>> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
>>>> Reviewed-by: Muchun Song <songmuchun@...edance.com>
>>>> ---
>>>> v1: https://lore.kernel.org/lkml/20220924053239.91661-1-zhengqi.arch@bytedance.com/
>>>>
>>>> Changelog in v1 -> v2:
>>>>    - change the subject and commit message (David)
>>>>
>>>>    mm/memory.c | 2 +-
>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/mm/memory.c b/mm/memory.c
>>>> index 118e5f023597..9e11c783ba0e 100644
>>>> --- a/mm/memory.c
>>>> +++ b/mm/memory.c
>>>> @@ -4122,7 +4122,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
>>>>        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;
>>>>        }
>>>
>>>
>>> Staring at 7df676974359, it indeed looks like an accidental use [nothing else in that patch uses update_mmu_cache].
>>>
>>> So it looks good to me, but a confirmation from Bibo Mao might be good.
>>
>> Thanks, and Hi Bibo, any comments here? :)
> 
> update_mmu_tlb is defined as empty on loongarch, maybe some lines should
> be added in file arch/loongarch/include/asm/pgtable.h like this:

Seems like a bug? Because there are many other places where
update_mmu_tlb() is called.

> 
> +#define __HAVE_ARCH_UPDATE_MMU_TLB
> +#define update_mmu_tlb  update_mmu_cache

If so, I can make the above as a separate fix patch.

Thanks,
Qi

> 
> regards
> bibo mao
>>
>>>
>>
> 

-- 
Thanks,
Qi