linux-kernel - Re: [PATCH v3 0/6] hugetlb_cgroup: Add hugetlb

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Date:   Wed, 28 Aug 2019 10:58:00 -0700
From:   Mina Almasry <almasrymina@...gle.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>, shuah <shuah@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Greg Thelen <gthelen@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        khalid.aziz@...cle.com, open list <linux-kernel@...r.kernel.org>,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
        cgroups@...r.kernel.org,
        Aneesh Kumar <aneesh.kumar@...ux.vnet.ibm.com>,
        Michal Koutný <mkoutny@...e.com>
Subject: Re: [PATCH v3 0/6] hugetlb_cgroup: Add hugetlb_cgroup reservation limits

On Wed, Aug 28, 2019 at 4:23 AM Michal Hocko <mhocko@...nel.org> wrote:
>
> On Mon 26-08-19 16:32:34, Mina Almasry wrote:
> >  mm/hugetlb.c                                  | 493 ++++++++++++------
> >  mm/hugetlb_cgroup.c                           | 187 +++++--
>
> This is a lot of changes to an already subtle code which hugetlb
> reservations undoubly are.

For what it's worth, I think this patch series is a net decrease in
the complexity of the reservation code, especially the region_*
functions, which is where a lot of the complexity lies. I removed the
race between region_del and region_{add|chg}, refactored the main
logic into smaller code, moved common code to helpers and deleted the
duplicates, and finally added lots of comments to the hard to
understand pieces. I hope that when folks review the changes they will
see that! :)

> Moreover cgroupv1 is feature frozen and I am
> not aware of any plans to port the controller to v2.

Also for what it's worth, if porting the controller to v2 is a
requisite to take this, I'm happy to do that. As far as I understand
there is no reason hugetlb_cgroups shouldn't be in cgroups v2, and we
see value in them.

> That all doesn't
> sound in favor of this change. Mike is the maintainer of the hugetlb
> code so I will defer to him to make a decision but I wouldn't recommend
> that.
> --
> Michal Hocko
> SUSE Labs