linux-kernel - Re: [RFC][PATCH 1/2] memcg: Ensure every task that uses an mm is in the same memory cgroup

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Message-ID: <87bmcuv0k0.fsf@xmission.com>
Date:   Fri, 01 Jun 2018 13:11:59 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Tejun Heo <tj@...nel.org>
Cc:     Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Kirill Tkhai <ktkhai@...tuozzo.com>, peterz@...radead.org,
        viro@...iv.linux.org.uk, mingo@...nel.org,
        paulmck@...ux.vnet.ibm.com, keescook@...omium.org, riel@...hat.com,
        tglx@...utronix.de, kirill.shutemov@...ux.intel.com,
        marcos.souza.org@...il.com, hoeun.ryu@...il.com,
        pasha.tatashin@...cle.com, gs051095@...il.com, dhowells@...hat.com,
        rppt@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
        Balbir Singh <balbir@...ux.vnet.ibm.com>,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: [RFC][PATCH 1/2] memcg: Ensure every task that uses an mm is in the same memory cgroup

Tejun Heo <tj@...nel.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