Re: [PATCH v3 0/6] hugetlb_cgroup: Add hugetlb_cgroup reservation limits

From: Michal Hocko <mhocko@kernel.org>
To: Mina Almasry <almasrymina@google.com>
Cc: "Mike Kravetz" <mike.kravetz@oracle.com>,
	shuah <shuah@kernel.org>, "David Rientjes" <rientjes@google.com>,
	"Shakeel Butt" <shakeelb@google.com>,
	"Greg Thelen" <gthelen@google.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	khalid.aziz@oracle.com,
	"open list" <linux-kernel@vger.kernel.org>,
	linux-mm@kvack.org, linux-kselftest@vger.kernel.org,
	cgroups@vger.kernel.org,
	"Aneesh Kumar" <aneesh.kumar@linux.vnet.ibm.com>,
	"Michal Koutný" <mkoutny@suse.com>, "Tejun Heo" <tj@kernel.org>,
	"Johannes Weiner" <hannes@cmpxchg.org>,
	"Li Zefan" <lizefan@huawei.com>
Subject: Re: [PATCH v3 0/6] hugetlb_cgroup: Add hugetlb_cgroup reservation limits
Date: Thu, 29 Aug 2019 09:18:07 +0200	[thread overview]
Message-ID: <20190829071807.GR28313@dhcp22.suse.cz> (raw)
In-Reply-To: <CAHS8izPPhPoqh-J9LJ40NJUCbgTFS60oZNuDSHmgtMQiYw72RA@mail.gmail.com>

[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@kernel.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