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From:   Suren Baghdasaryan <surenb@google.com>
Date:   Mon, 17 Apr 2023 15:47:57 -0700
Message-ID: <CAJuCfpHf06cr2d277DXQUtBto_0bVgK3ykMHLYRgZXgnot=e4w@mail.gmail.com>
Subject: Re: [PATCH v2 1/1] mm: do not increment pgfault stats when page fault
 handler retries
To:     Peter Xu <peterx@redhat.com>
Cc:     akpm@linux-foundation.org, willy@infradead.org, hannes@cmpxchg.org,
        mhocko@suse.com, josef@toxicpanda.com, jack@suse.cz,
        ldufour@linux.ibm.com, laurent.dufour@fr.ibm.com,
        michel@lespinasse.org, liam.howlett@oracle.com, jglisse@google.com,
        vbabka@suse.cz, minchan@google.com, dave@stgolabs.net,
        punit.agrawal@bytedance.com, lstoakes@gmail.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        kernel-team@android.com
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On Mon, Apr 17, 2023 at 2:26=E2=80=AFPM Peter Xu <peterx@redhat.com> wrote:
>
> On Fri, Apr 14, 2023 at 05:08:18PM -0700, Suren Baghdasaryan wrote:
> > @@ -5223,8 +5230,8 @@ vm_fault_t handle_mm_fault(struct vm_area_struct =
*vma, unsigned long address,
> >               if (task_in_memcg_oom(current) && !(ret & VM_FAULT_OOM))
> >                       mem_cgroup_oom_synchronize(false);
> >       }
> > -
> > -     mm_account_fault(regs, address, flags, ret);
> > +out:
> > +     mm_account_fault(mm, regs, address, flags, ret);
>
> Ah, one more question.. can this cached mm race with a destroying mm (jus=
t
> like the vma race we wanted to avoid)?  Still a question only applies to
> COMPLETE case when mmap read lock can be released.  Thanks,

I believe that is impossible because whoever is calling the page fault
handler has stabilized the mm by getting a refcount.

>
> >
> >       return ret;
> >  }
>
> --
> Peter Xu
>