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

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Date:   Thu, 23 Feb 2023 14:17:18 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Yosry Ahmed <yosryahmed@...gle.com>,
        "T.J. Mercier" <tjmercier@...gle.com>,
        Alistair Popple <apopple@...dia.com>,
        Michal Hocko <mhocko@...e.com>, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        jhubbard@...dia.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

On Thu, Feb 23, 2023 at 08:15:17AM -1000, Tejun Heo wrote:
> On Thu, Feb 23, 2023 at 02:10:56PM -0400, Jason Gunthorpe wrote:
> > > I am not familiar with memfd, but based on
> > > mem_cgroup_swapin_charge_folio() it seems like if cgroup B swapped in
> > > the pages they will remain charged to cgroup A, unless cgroup A is
> > > removed/offlined. Am I missing something?
> > 
> > Ah, I don't know, Tejun said:
> > 
> > "but it can converge when page usage transfers across cgroups
> > if needed."
> > 
> > Which I assumed was swap related but I don't know how convergence
> > works.
> 
> That'd work for pagecache. For swap-backed, I think Yosry is right. Is
> MAP_SHARED | MAP_ANONYMOUS a concern? Such mappings can only be shared
> through forking, so it's not a common thing to be shared across different
> resource domains.

Isn't memfd also in the same boat?

Jason