linux-kernel - Re: [PATCH 14/19] mm: Introduce a cgroup for pinned memory

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Message-ID: <Y+GcJQRhvjqFaaSp@mtj.duckdns.org>
Date:   Mon, 6 Feb 2023 14:32:37 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Yosry Ahmed <yosryahmed@...gle.com>,
        Alistair Popple <apopple@...dia.com>, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        jhubbard@...dia.com, tjmercier@...gle.com, hannes@...xchg.org,
        surenb@...gle.com, mkoutny@...e.com, daniel@...ll.ch,
        "Daniel P . Berrange" <berrange@...hat.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Zefan Li <lizefan.x@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 14/19] mm: Introduce a cgroup for pinned memory

Hello,

On Mon, Feb 06, 2023 at 07:40:55PM -0400, Jason Gunthorpe wrote:
> (a) kind of destroys the point of this as a sandboxing tool
> 
> It is not so harmful to use memory that someone else has been charged
> with allocating.
> 
> But it is harmful to pin memory if someone else is charged for the
> pin. It means it is unpredictable how much memory a sandbox can
> actually lock down.
> 
> Plus we have the double accounting problem, if 1000 processes in
> different cgroups open the tmpfs and all pin the memory then cgroup A
> will be charged 1000x for the memory and hit its limit, possibly
> creating a DOS from less priv to more priv

Let's hear what memcg people think about it. I'm not a fan of disassociating
the ownership and locker of the same page but it is true that actively
increasing locked consumption on a remote cgroup is awkward too.

Thanks.

-- 
tejun