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Tue, 24 Feb 2026 01:42:12 -0800 (PST) Date: Tue, 24 Feb 2026 10:42:12 +0100 From: Maxime Ripard To: "T.J. Mercier" Cc: Eric Chanudet , Sumit Semwal , Benjamin Gaignard , Brian Starkey , John Stultz , Christian =?utf-8?B?S8O2bmln?= , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org, Albert Esteve , linux-mm@kvack.org, Yosry Ahmed , Shakeel Butt Subject: Re: [PATCH v2 0/3] dma-buf: heaps: cma: enable dmem cgroup accounting Message-ID: <20260224-terrestrial-jaguarundi-of-influence-e3ccf1@houat> References: <20260218-dmabuf-heap-cma-dmem-v2-0-b249886fb7b2@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha384; protocol="application/pgp-signature"; boundary="zryjcv333aysdxbr" Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam09 X-Stat-Signature: areaggcgemduu6x5i6561q6nxykab979 X-Rspamd-Queue-Id: 34CB5120005 X-Rspam-User: X-HE-Tag: 1771926138-306358 X-HE-Meta: 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 m83j7LMQ 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: --zryjcv333aysdxbr Content-Type: text/plain; protected-headers=v1; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Subject: Re: [PATCH v2 0/3] dma-buf: heaps: cma: enable dmem cgroup accounting MIME-Version: 1.0 Hi TJ, On Thu, Feb 19, 2026 at 05:14:42PM -0800, T.J. Mercier wrote: > On Wed, Feb 18, 2026 at 9:15=E2=80=AFAM Eric Chanudet wrote: > > An earlier series[1] from Maxime introduced dmem to the cma allocator in > > an attempt to use it generally for dma-buf. Restart from there and apply > > the charge in the narrower context of the CMA dma-buf heap instead. > > > > In line with introducing cgroup to the system heap[2], this behavior is > > enabled based on dma_heap.mem_accounting, disabled by default. > > > > dmem is chosen for CMA heaps as it allows limits to be set for each > > region backing each heap. The charge is only put in the dma-buf heap for > > now as it guaranties it can be accounted against a userspace process > > that requested the allocation. >=20 > But CMA memory is system memory, and regular (non-CMA) movable > allocations can occur out of these CMA areas. So this splits system > memory accounting between memcg (from [2]) and dmem. If I want to put > a limit on system memory use I have to adjust multiple limits (memcg + > dmems) and know how to divide the total between them all. >=20 > How do you envision using this combination of different controllers? I feel like it can be argued either way, and I don't really see a way out of supporting both. Like you pointed out, CMA can indeed be seen as system memory, but it's also a limited pool that you might want to place arbitrary limits on since, unlike system memory, it can't be reclaimed, will not trigger the OOM killer, and more generally is a much more sparse resource. Maxime --zryjcv333aysdxbr Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iJUEABMJAB0WIQTkHFbLp4ejekA/qfgnX84Zoj2+dgUCaZ1ycwAKCRAnX84Zoj2+ dm9VAX9JuCh6S7GJf/wUUY2RPjeN5/Hr5cmqHNDJmY78HFfnpCUW4mFYqDeZaoeP aK99/MkBf0bRStrApFYWF5JgHSK2oeVEEzJ9MxforcaAQ09KVjoG4RckJH53I57/ PQy+P4+J5A== =fLNZ -----END PGP SIGNATURE----- --zryjcv333aysdxbr--