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

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Message-ID: <e5cd4c46-71fd-8edb-098c-2ac839d5c5d2@loongson.cn>
Date:   Thu, 29 Sep 2022 11:27:54 +0800
From:   maobibo <maobibo@...ngson.cn>
To:     Qi Zheng <zhengqi.arch@...edance.com>,
        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

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:

+#define __HAVE_ARCH_UPDATE_MMU_TLB
+#define update_mmu_tlb  update_mmu_cache

regards
bibo mao
> 
>>
>