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

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Message-ID: <Y9RFs+90TyzVMs83@slm.duckdns.org>
Date:   Fri, 27 Jan 2023 11:44:19 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Alistair Popple <apopple@...dia.com>
Cc:     linux-mm@...ck.org, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, jgg@...dia.com, jhubbard@...dia.com,
        tjmercier@...gle.com, hannes@...xchg.org, surenb@...gle.com,
        mkoutny@...e.com, daniel@...ll.ch,
        Zefan Li <lizefan.x@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH 14/19] mm: Introduce a cgroup for pinned memory

On Tue, Jan 24, 2023 at 04:42:43PM +1100, Alistair Popple wrote:
> If too much memory in a system is pinned or locked it can lead to
> problems such as performance degredation or in the worst case
> out-of-memory errors as such memory cannot be moved or paged out.
> 
> In order to prevent users without CAP_IPC_LOCK from causing these
> issues the amount of memory that can be pinned is typically limited by
> RLIMIT_MEMLOCK. However this is inflexible as limits can't be shared
> between tasks and the enforcement of these limits is inconsistent
> between in-kernel users of pinned memory such as mlock() and device
> drivers which may also pin pages with pin_user_pages().
> 
> To allow for a single limit to be set introduce a cgroup controller
> which can be used to limit the number of pages being pinned by all
> tasks in the cgroup.

The use case makes some sense to me but I wonder whether this'd fit a lot
better in memcg rather than being its own controller.

Thanks.

-- 
tejun