linux-kernel - Re: [PATCH v2 1/1] mm: do not increment pgfault stats when page fault handler retries

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Date:   Mon, 17 Apr 2023 15:47:57 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     akpm@...ux-foundation.org, willy@...radead.org, hannes@...xchg.org,
        mhocko@...e.com, josef@...icpanda.com, jack@...e.cz,
        ldufour@...ux.ibm.com, laurent.dufour@...ibm.com,
        michel@...pinasse.org, liam.howlett@...cle.com, jglisse@...gle.com,
        vbabka@...e.cz, minchan@...gle.com, dave@...olabs.net,
        punit.agrawal@...edance.com, lstoakes@...il.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@...roid.com
Subject: Re: [PATCH v2 1/1] mm: do not increment pgfault stats when page fault
 handler retries

On Mon, Apr 17, 2023 at 2:26 PM Peter Xu <peterx@...hat.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 (just
> 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
>