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Fri, 23 Jan 2026 05:25:17 -0800 (PST) Date: Fri, 23 Jan 2026 14:25:16 +0100 From: Maxime Ripard To: Thierry Reding Cc: David Airlie , Simona Vetter , Sumit Semwal , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Benjamin Gaignard , Brian Starkey , John Stultz , "T . J . Mercier" , Andrew Morton , David Hildenbrand , Mike Rapoport , Sumit Garg , dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org, linux-tegra@vger.kernel.org, linaro-mm-sig@lists.linaro.org, linux-mm@kvack.org Subject: Re: [PATCH v2 04/10] mm/cma: Allow dynamically creating CMA areas Message-ID: <20260123-active-witty-rabbit-0fc5b9@houat> References: <20260122161009.3865888-1-thierry.reding@kernel.org> <20260122161009.3865888-5-thierry.reding@kernel.org> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha384; protocol="application/pgp-signature"; boundary="equ2x5ui66msv4bz" Content-Disposition: inline In-Reply-To: <20260122161009.3865888-5-thierry.reding@kernel.org> X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 08D891A0008 X-Stat-Signature: taa3hyyxhkz3hi6bfb6qzskuhp7fseq1 X-Rspam-User: X-HE-Tag: 1769174723-124776 X-HE-Meta: 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 +cAO1fvd /J+bVBGb0j3dUhIspblG7/8H30+sGQWQgfiFGfK0LU+MxfBLQqTSZQiUquai+hEcFYjIPtMjkX70VhQkirNb3xx+i4rxKwn33lLM6TqLsp8/S1tYeroVQVvcASZjRrLXHGO5qiSo2LNPIx00flj7pExNFZ6wnFpbJqaFBGGsAsAL/oj0epEjPPyOw2PTuEPFqJE1QNDTjq04m1ejNA59UIV3HTu3mBKM5Us+JLmJIDO2YBZRVND5wlES79QneIZtLxrJ6u1ujYxn/ZByeQZx8AjS8BrFH/uXOAbxIsOYJSNHahjuy3gds0VPm++5oS5auJjOL88qvNWUXmPiMgkEfSBH1aA== 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: --equ2x5ui66msv4bz Content-Type: text/plain; protected-headers=v1; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Subject: Re: [PATCH v2 04/10] mm/cma: Allow dynamically creating CMA areas MIME-Version: 1.0 On Thu, Jan 22, 2026 at 05:10:03PM +0100, Thierry Reding wrote: > From: Thierry Reding >=20 > There is no technical reason why there should be a limited number of CMA > regions, so extract some code into helpers and use them to create extra > functions (cma_create() and cma_free()) that allow creating and freeing, > respectively, CMA regions dynamically at runtime. >=20 > The static array of CMA areas cannot be replaced by dynamically created > areas because for many of them, allocation must not fail and some cases > may need to initialize them before the slab allocator is even available. > To account for this, keep these "early" areas in a separate list and > track the dynamic areas in a separate list. >=20 > Signed-off-by: Thierry Reding AFAIU, this won't create a new cma heap when registering. This goes against the recent work we did to create one for every cma region. I guess, since you have a driver that would explicitly handle that region, we should create some kind of opt-out mechanism, but by default, we should still create such a heap. That being said, it's not clear to me why the heap driver uses CMA in the first place. Maxime --equ2x5ui66msv4bz Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iJUEABMJAB0WIQTkHFbLp4ejekA/qfgnX84Zoj2+dgUCaXN2tQAKCRAnX84Zoj2+ dtsNAYD+XKsLdRQjkWGztlo6ccvGIarpCsAjHJYFv0zPbdpfdWvfyLFS1lY/kTQQ 0g9g6Z8Bf0j4St2GiD6RINFxEH7YvowARYnLD4kKLHV0CjY6XFcfRV2lK+cZmof9 IIFG/01OiA== =as/Q -----END PGP SIGNATURE----- --equ2x5ui66msv4bz--