linux-kernel - Re: [PATCH v6] hugetlb: Add hugetlb.*.numa

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Message-ID: <CAMZfGtVjrMC1+fm6JjQfwFHeZN3dcddaAogZsHFEtL4HJyhYUw@mail.gmail.com>
Date:   Sat, 13 Nov 2021 10:44:41 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     Mina Almasry <almasrymina@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        David Rientjes <rientjes@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>, Jue Wang <juew@...gle.com>,
        Yang Yao <ygyao@...gle.com>, Joanna Li <joannali@...gle.com>,
        Cannon Matthews <cannonmatthews@...gle.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6] hugetlb: Add hugetlb.*.numa_stat file

On Sat, Nov 13, 2021 at 7:36 AM Mike Kravetz <mike.kravetz@...cle.com> wrote:
>
> Subject:   Re: [PATCH v6] hugetlb: Add hugetlb.*.numa_stat file
>
> To:        Muchun Song <songmuchun@...edance.com>, Mina Almasry <almasrymina@...gle.com>
>
> Cc:        Andrew Morton <akpm@...ux-foundation.org>, Shuah Khan <shuah@...nel.org>, Miaohe Lin <linmiaohe@...wei.com>, Oscar Salvador <osalvador@...e.de>, Michal Hocko <mhocko@...e.com>, David Rientjes <rientjes@...gle.com>, Shakeel Butt <shakeelb@...gle.com>, Jue Wang <juew@...gle.com>, Yang Yao <ygyao@...gle.com>, Joanna Li <joannali@...gle.com>, Cannon Matthews <cannonmatthews@...gle.com>, Linux Memory Management List <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>
>
> Bcc:
>
> -=-=-=-=-=-=-=-=-=# Don't remove this line #=-=-=-=-=-=-=-=-=-
>
> On 11/10/21 6:36 PM, Muchun Song wrote:
>
> > On Thu, Nov 11, 2021 at 9:50 AM Mina Almasry <almasrymina@...gle.com> wrote:
>
> >>
>
> >> +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
>