Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   ebiederm@xmission.com (Eric W. Biederman)
To:     Tejun Heo <tj@kernel.org>
Cc:     Michal Hocko <mhocko@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Kirill Tkhai <ktkhai@virtuozzo.com>, peterz@infradead.org,
        viro@zeniv.linux.org.uk, mingo@kernel.org,
        paulmck@linux.vnet.ibm.com, keescook@chromium.org, riel@redhat.com,
        tglx@linutronix.de, kirill.shutemov@linux.intel.com,
        marcos.souza.org@gmail.com, hoeun.ryu@gmail.com,
        pasha.tatashin@oracle.com, gs051095@gmail.com, dhowells@redhat.com,
        rppt@linux.vnet.ibm.com, linux-kernel@vger.kernel.org,
        Balbir Singh <balbir@linux.vnet.ibm.com>,
        Oleg Nesterov <oleg@redhat.com>
References: <20180510121418.GD5325@dhcp22.suse.cz>
        <20180522125757.GL20020@dhcp22.suse.cz> <87wovu889o.fsf@xmission.com>
        <20180524111002.GB20441@dhcp22.suse.cz>
        <20180524141635.c99b7025a73a709e179f92a2@linux-foundation.org>
        <20180530121721.GD27180@dhcp22.suse.cz> <87wovjacrh.fsf@xmission.com>
        <87wovj8e1d.fsf_-_@xmission.com> <87y3fywodn.fsf_-_@xmission.com>
        <87sh66wobu.fsf_-_@xmission.com>
        <20180601165034.GX1351649@devbig577.frc2.facebook.com>
Date:   Fri, 01 Jun 2018 13:11:59 -0500
In-Reply-To: <20180601165034.GX1351649@devbig577.frc2.facebook.com> (Tejun
        Heo's message of "Fri, 1 Jun 2018 09:50:34 -0700")
Message-ID: <87bmcuv0k0.fsf@xmission.com>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux)
MIME-Version: 1.0
Content-Type: text/plain
Subject: Re: [RFC][PATCH 1/2] memcg: Ensure every task that uses an mm is in the same memory cgroup
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Tejun Heo <tj@kernel.org> writes:

>> This effectively forbids process with mm's shared processes being migrated.
>> Although enabling the control file might work.
>
> So, I don't think we need to support putting tasks which share a mm in
> different cgroups.  That said, if we're gonna put in that restriction,
> I think it should be in cgroup core rather than memcg can_attach.  The
> only thing we'd need to do is widening what cgroup migration considers
> to be a process.

Widening the definition of a process sounds good.  The memory control
group code would still need a way to forbid these in cgroup v1 mode,
when someone uses the task file.

Using widening instead of denying should reduce the risk of introducing
a regression.

The only reason I support the crazy case in my earlier patch is so that
we can have this discussion and in case we do cause a regression with
this change the previous algorithmic cleanup won't have to be reverted
as well.

Eric