linux-kernel - Re: [PATCH v8] hugetlb: Add hugetlb.*.numa

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Date:   Mon, 22 Nov 2021 17:20:59 -0800
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Mina Almasry <almasrymina@...gle.com>
Cc:     Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Mike Kravetz <mike.kravetz@...cle.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>,
        Muchun Song <songmuchun@...edance.com>,
        David Rientjes <rientjes@...gle.com>,
        Jue Wang <juew@...gle.com>, Yang Yao <ygyao@...gle.com>,
        Joanna Li <joannali@...gle.com>,
        Cannon Matthews <cannonmatthews@...gle.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v8] hugetlb: Add hugetlb.*.numa_stat file

On Mon, Nov 22, 2021 at 4:10 PM Mina Almasry <almasrymina@...gle.com> wrote:
>
> For hugetlb backed jobs/VMs it's critical to understand the numa
> information for the memory backing these jobs to deliver optimal
> performance.
>
> Currently this technically can be queried from /proc/self/numa_maps, but
> there are significant issues with that. Namely:
> 1. Memory can be mapped or unmapped.
> 2. numa_maps are per process and need to be aggregated across all
>    processes in the cgroup. For shared memory this is more involved as
>    the userspace needs to make sure it doesn't double count shared
>    mappings.
> 3. I believe querying numa_maps needs to hold the mmap_lock which adds
>    to the contention on this lock.
>
> For these reasons I propose simply adding hugetlb.*.numa_stat file,
> which shows the numa information of the cgroup similarly to
> memory.numa_stat.
>
> On cgroup-v2:
>    cat /sys/fs/cgroup/unified/test/hugetlb.2MB.numa_stat
>    total=2097152 N0=2097152 N1=0
>
> On cgroup-v1:
>    cat /sys/fs/cgroup/hugetlb/test/hugetlb.2MB.numa_stat
>    total=2097152 N0=2097152 N1=0
>    hierarichal_total=2097152 N0=2097152 N1=0
>
> This patch was tested manually by allocating hugetlb memory and querying
> the hugetlb.*.numa_stat file of the cgroup and its parents.
> 
> Cc: Mike Kravetz <mike.kravetz@...cle.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Shuah Khan <shuah@...nel.org>
> Cc: Miaohe Lin <linmiaohe@...wei.com>
> Cc: Oscar Salvador <osalvador@...e.de>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Muchun Song <songmuchun@...edance.com>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Shakeel Butt <shakeelb@...gle.com>
> Cc: Jue Wang <juew@...gle.com>
> Cc: Yang Yao <ygyao@...gle.com>
> Cc: Joanna Li <joannali@...gle.com>
> Cc: Cannon Matthews <cannonmatthews@...gle.com>
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
>
> Signed-off-by: Mina Almasry <almasrymina@...gle.com>
>

Reviewed-by: Shakeel Butt <shakeelb@...gle.com>