linux-kernel - Re: [RFC 0/3] cgroups: Add support for pinned device memory

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Message-ID: <dc21e54c-d7ae-4d7e-9acb-6a3fa573b20f@redhat.com>
Date: Mon, 1 Sep 2025 14:25:14 +0200
From: David Hildenbrand <david@...hat.com>
To: Maarten Lankhorst <dev@...khorst.se>,
 Lucas De Marchi <lucas.demarchi@...el.com>,
 'Thomas Hellström' <thomas.hellstrom@...ux.intel.com>,
 Rodrigo Vivi <rodrigo.vivi@...el.com>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Maxime Ripard <mripard@...nel.org>,
 Natalie Vock <natalie.vock@....de>, Tejun Heo <tj@...nel.org>,
 Johannes Weiner <hannes@...xchg.org>, 'Michal Koutný'
 <mkoutny@...e.com>, Michal Hocko <mhocko@...nel.org>,
 Roman Gushchin <roman.gushchin@...ux.dev>,
 Shakeel Butt <shakeel.butt@...ux.dev>, Muchun Song <muchun.song@...ux.dev>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "'Liam R . Howlett'" <Liam.Howlett@...cle.com>,
 Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
 Suren Baghdasaryan <surenb@...gle.com>,
 Thomas Zimmermann <tzimmermann@...e.de>
Cc: Michal Hocko <mhocko@...e.com>, intel-xe@...ts.freedesktop.org,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 cgroups@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC 0/3] cgroups: Add support for pinned device memory

On 19.08.25 13:49, Maarten Lankhorst wrote:
> When exporting dma-bufs to other devices, even when it is allowed to use
> move_notify in some drivers, performance will degrade severely when
> eviction happens.
> 
> A perticular example where this can happen is in a multi-card setup,
> where PCI-E peer-to-peer is used to prevent using access to system memory.
> 
> If the buffer is evicted to system memory, not only the evicting GPU wher
> the buffer resided is affected, but it will also stall the GPU that is
> waiting on the buffer.
> 
> It also makes sense for long running jobs not to be preempted by having
> its buffers evicted, so it will make sense to have the ability to pin
> from system memory too.
> 
> This is dependant on patches by Dave Airlie, so it's not part of this
> series yet. But I'm planning on extending pinning to the memory cgroup
> controller in the future to handle this case.
> 
> Implementation details:
> 
> For each cgroup up until the root cgroup, the 'min' limit is checked
> against currently effectively pinned value. If the value will go above
> 'min', the pinning attempt is rejected.
> 
> Pinned memory is handled slightly different and affects calculating
> effective min/low values. Pinned memory is subtracted from both,
> and needs to be added afterwards when calculating.

The term "pinning" is overloaded, and frequently we refer to 
pin_user_pages() and friends.

So I'm wondering if there is an alternative term to describe what you 
want to achieve.

Is it something like "unevictable" ?

-- 
Cheers

David / dhildenb