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

From: Mina Almasry <almasrymina@google.com>
To: Michal Hocko <mhocko@kernel.org>
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>
Subject: Re: [PATCH v3 0/6] hugetlb_cgroup: Add hugetlb_cgroup reservation limits
Date: Wed, 28 Aug 2019 10:58:00 -0700	[thread overview]
Message-ID: <CAHS8izPPhPoqh-J9LJ40NJUCbgTFS60oZNuDSHmgtMQiYw72RA@mail.gmail.com> (raw)
In-Reply-To: <20190828112340.GB7466@dhcp22.suse.cz>

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! :)

> 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