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

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Date:   Thu, 29 Aug 2019 09:18:07 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Mina Almasry <almasrymina@...gle.com>
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>,
        Tejun Heo <tj@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Li Zefan <lizefan@...wei.com>
Subject: Re: [PATCH v3 0/6] hugetlb_cgroup: Add hugetlb_cgroup reservation
 limits

[Cc cgroups maintainers]

On Wed 28-08-19 10:58:00, Mina Almasry wrote:
> 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! :)

Post those improvements as standalone patches and sell them as
improvements. We can talk about the net additional complexity of the
controller much easier then.

> > 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.

Talk to cgroups maintainers why the hugegetlb controller hasn't been
enabled in v2. All I am saing is that v1 only features are really a hard
sell. Even without adding a lot of code to hugetlb which is quite
complex on its own.
-- 
Michal Hocko
SUSE Labs