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

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Message-ID: <b702cc9.d17c.1838865fb5c.Coremail.chenhuacai@loongson.cn>
Date:   Thu, 29 Sep 2022 16:38:48 +0800 (GMT+08:00)
From:   陈华才 <chenhuacai@...ngson.cn>
To:     maobibo <maobibo@...ngson.cn>
Cc:     "Qi Zheng" <zhengqi.arch@...edance.com>,
        "David Hildenbrand" <david@...hat.com>, akpm@...ux-foundation.org,
        muchun.song@...ux.dev, chris@...kel.net, jcmvbkbc@...il.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        "Muchun Song" <songmuchun@...edance.com>
Subject: Re: Re: [PATCH v2] mm: use update_mmu_tlb() on the second thread

Hi, all,


> -----原始邮件-----
> 发件人: maobibo <maobibo@...ngson.cn>
> 发送时间:2022-09-29 12:05:33 (星期四)
> 收件人: "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>
> 抄送: chris@...kel.net, jcmvbkbc@...il.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org, "Muchun Song" <songmuchun@...edance.com>
> 主题: Re: [PATCH v2] mm: use update_mmu_tlb() on the second thread
> 
> 
> 
> 在 2022/9/29 11:47, Qi Zheng 写道:
> > 
> > 
> > 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.
> It sounds good to me.  
> 
> Huacai, do you have any comments?
From my point of view, LoongArch need a fix for this.

Huacai
> 
> regards
> bibo, mao
> > 
> > Thanks,
> > Qi
> > 
> >>
> >> regards
> >> bibo mao
> >>>
> >>>>
> >>>
> >>
> > 


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