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From:   Muchun Song <songmuchun@bytedance.com>
Date:   Sat, 13 Nov 2021 10:44:41 +0800
Message-ID: <CAMZfGtVjrMC1+fm6JjQfwFHeZN3dcddaAogZsHFEtL4HJyhYUw@mail.gmail.com>
Subject: Re: [PATCH v6] hugetlb: Add hugetlb.*.numa_stat file
To:     Mike Kravetz <mike.kravetz@oracle.com>
Cc:     Mina Almasry <almasrymina@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Shuah Khan <shuah@kernel.org>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Oscar Salvador <osalvador@suse.de>,
        Michal Hocko <mhocko@suse.com>,
        David Rientjes <rientjes@google.com>,
        Shakeel Butt <shakeelb@google.com>, Jue Wang <juew@google.com>,
        Yang Yao <ygyao@google.com>, Joanna Li <joannali@google.com>,
        Cannon Matthews <cannonmatthews@google.com>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Sat, Nov 13, 2021 at 7:36 AM Mike Kravetz <mike.kravetz@oracle.com> wrot=
e:
>
> Subject:   Re: [PATCH v6] hugetlb: Add hugetlb.*.numa_stat file
>
> To:        Muchun Song <songmuchun@bytedance.com>, Mina Almasry <almasrym=
ina@google.com>
>
> Cc:        Andrew Morton <akpm@linux-foundation.org>, Shuah Khan <shuah@k=
ernel.org>, Miaohe Lin <linmiaohe@huawei.com>, Oscar Salvador <osalvador@su=
se.de>, Michal Hocko <mhocko@suse.com>, David Rientjes <rientjes@google.com=
>, Shakeel Butt <shakeelb@google.com>, Jue Wang <juew@google.com>, Yang Yao=
 <ygyao@google.com>, Joanna Li <joannali@google.com>, Cannon Matthews <cann=
onmatthews@google.com>, Linux Memory Management List <linux-mm@kvack.org>, =
LKML <linux-kernel@vger.kernel.org>
>
> Bcc:
>
> -=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D# Don't remove this line #=3D-=3D-=3D=
-=3D-=3D-=3D-=3D-=3D-=3D-
>
> On 11/10/21 6:36 PM, Muchun Song wrote:
>
> > On Thu, Nov 11, 2021 at 9:50 AM Mina Almasry <almasrymina@google.com> w=
rote:
>
> >>
>
> >> +struct hugetlb_cgroup_per_node {
>
> >> +       /* hugetlb usage in pages over all hstates. */
>
> >> +       atomic_long_t usage[HUGE_MAX_HSTATE];
>
> >
>
> > Why do you use atomic? IIUC, 'usage' is always
>
> > increased/decreased under hugetlb_lock except
>
> > hugetlb_cgroup_read_numa_stat() which is always
>
> > reading it. So I think WRITE_ONCE/READ_ONCE
>
> > is enough.
>
>
>
> Thanks for continuing to work this, I was traveling and unable to
>
> comment.

Have a good time.

>
>
>
> Unless I am missing something, I do not see a reason for WRITE_ONCE/READ_=
ONCE

Because __hugetlb_cgroup_commit_charge and
hugetlb_cgroup_read_numa_stat can run parallely,
which meets the definition of data race. I believe
KCSAN could report this race. I'm not strongly
suggest using WRITE/READ_ONCE() here. But
in theory it should be like this. Right?

Thanks.

>
> and would suggest going back to the way this code was in v5.
>
> --
>
> Mike Kravetz
>