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[2003:e4:1f1c:4d00:f22f:74ff:fe1f:3a53]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3cf34494776sm23960790f8f.61.2025.09.03.09.12.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 03 Sep 2025 09:12:22 -0700 (PDT) Date: Wed, 3 Sep 2025 18:12:19 +0200 From: Thierry Reding To: David Hildenbrand Cc: Frank van der Linden , David Airlie , Simona Vetter , Sumit Semwal , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Benjamin Gaignard , Brian Starkey , John Stultz , "T.J. Mercier" , Andrew Morton , Mike Rapoport , 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 3/9] mm/cma: Allow dynamically creating CMA areas Message-ID: References: <20250902154630.4032984-1-thierry.reding@gmail.com> <20250902154630.4032984-4-thierry.reding@gmail.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="nfbiwxgfuwekt25w" Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: F36FD40019 X-Stat-Signature: wkjfgek4y6ohmqj1bz77beeo3i6nb8c7 X-HE-Tag: 1756915944-134284 X-HE-Meta: U2FsdGVkX19CTBDki+RZI0R0gpxEQBU2mmXIC7MN1PQ9ChHnyunSqwVBG93jNO1A0ULdg16tLTTq2dkjwKhOmn9+DRAczTtmYjcaG3ROtjaWjSTieU+Dvb80E47dEKoe16NDGDjau3JojCNY3AaWscGe7nYFHAUfZAjvvIKuBOqcSqHB7ExMVYjMb6O7DGheFmolpOKmp0hTNZ+n0DmfnZpnWPjFT0JccAAfYbTM7B4jigTNHbi/adO1lo2/hTjWXq0j/GEGYaDFKtDcGVasJn6ptFDv7zecgL4TqRYtG/TAt47/K/6YCOZmABJ8rli1ecE1OkjgGMP/6z+fRL1tnjZkWO7iL7T5UqDxALOwQi4R07U13qlMmhfDknPrcEvp503E54LBgzf+up640SMHbfH7WG/3SV7Ar0YeewNeJ18aPS7zVJVpv89hdpyjSZnKASejeKmEPwxNqon7QzebX3RsZ2qo8l/HbFOQ0Ao+ZBLhnZk4gt+hhTdbJ46gUr7d3cmLncCUDlPJ6XgQ8rGgPZQEo69KtEvTQgPSeXZRGQk2iT67KINfoVSOpF6vUY0MBRmCmT8mz/XiztnusQq4wP+OpxNGWKNh8voHUJJ+xZJHdOJD7dXQy0Pxfn35vfhhR3B8yMjNERmsHY/NGPfTRtdZheE6m3Mzp+JfeRDubtKSJ/6VC8ccEffr1UWIYrw3kFBnHAhn/xhjjLDXr1c0isKzBVEUDoFCHn+8cMQ506hdv0Q5Z8LhiGKC2ryJqpqzeDBmRA98q4tfSFIfFvSeJIVpfQ86uKBlr3q47x5F9rCJLf+hfpSaoOjap8QmYfxzb5vGy/nvoCCBDwa15zDP0Rni+SY8uFMPeZYUXNVRCz3Fx4USTzylFVrDX1F+zDt/g9DSLm1k13LVuxxYVIguOU3IAwV61+37+JNy5ucEd41Wb5XPIeUf2CtS24mcQiWIIJHqcUJl3gBT6SyfyJ7 IQ+oAxrN 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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: --nfbiwxgfuwekt25w Content-Type: text/plain; protected-headers=v1; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Subject: Re: [PATCH 3/9] mm/cma: Allow dynamically creating CMA areas MIME-Version: 1.0 On Tue, Sep 02, 2025 at 09:04:24PM +0200, David Hildenbrand wrote: >=20 > > > +>> +struct cma *__init cma_create(phys_addr_t base, phys_addr_t size, > > > + unsigned int order_per_bit, const char = *name) > > > +{ > > > + struct cma *cma; > > > + int ret; > > > + > > > + ret =3D cma_check_memory(base, size); > > > + if (ret < 0) > > > + return ERR_PTR(ret); > > > + > > > + cma =3D kzalloc(sizeof(*cma), GFP_KERNEL); > > > + if (!cma) > > > + return ERR_PTR(-ENOMEM); > > > + > > > + cma_init_area(cma, name, size, order_per_bit); > > > + cma->ranges[0].base_pfn =3D PFN_DOWN(base); > > > + cma->ranges[0].early_pfn =3D PFN_DOWN(base); > > > + cma->ranges[0].count =3D cma->count; > > > + cma->nranges =3D 1; > > > + > > > + cma_activate_area(cma); > > > + > > > + return cma; > > > +} > > > + > > > +void cma_free(struct cma *cma) > > > +{ > > > + kfree(cma); > > > +} > > > -- > > > 2.50.0 > >=20 > >=20 > > I agree that supporting dynamic CMA areas would be good. However, by > > doing it like this, these CMA areas are invisible to the rest of the > > system. E.g. cma_for_each_area() does not know about them. It seems a > > bit inconsistent that there will now be some areas that are globally > > known, and some that are not. >=20 > Yeah, I'm not a fan of that. >=20 > What is the big problem we are trying to solve here? Why do they have to = be > dynamic, why do they even have to support freeing? Freeing isn't necessarily something that I've needed. It just seemed like there wasn't really a good reason not to support it. The current implementation here is not sufficient, though, because we'd need to properly undo everything that cma_activate_area() does. I think the cleanup: block in cma_activate_area() is probably sufficient. The problem that I'm trying to solve is that currently, depending on the use-case the kernel configuration needs to be changed and the kernel rebuilt in order to support it. However there doesn't seem to be a good technical reason for that limitation. The only reason it is this way seems to be that, well, it's always been this way. Thierry --nfbiwxgfuwekt25w Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAABCgAdFiEEiOrDCAFJzPfAjcif3SOs138+s6EFAmi4aOMACgkQ3SOs138+ s6EWag//TG8GKL8D+KtYbrfxxwO/AEt7PxS9tKNaQ4uX/W4JVPtJSVqumPpLlATz kSWcKAk8uyNWVRifoC26e2FU+eTup+VsLHQK/3g6/EEv0rt/jn5mJWu91ckJuH+N nWHOeXCqeuGYN01d2wYby1PZ6Mtvbe6PlBifyLpvoAsUpN1n4HvE1CWu45gZIR5d 2WqzOWqLtDf4dyhpPKzu3xwXMgms8SyLEY64ulTMjg02QvIFPhJ/EN3VMs20tuX7 1UBiq4yw7ylaSoKAUdFEB9sOq4tpnoi9YY9fgoMhnCvwP5wZFwKbqYIhfGqzEGWo Yad3Oba0P1qxdCFeOabbitgjRtZQO8pJNfGuJImpP4fE8Bz547KcSbcORfZvu16h lJENGR4OXALHeSbgAELkUWTBnxAEHs356KGRoIxOarNda5xvFHp9joOODPz5s/j8 kIeQjrt23Vl4uqqlzr2n8ZwIQY6Whc2OuPnY/1/sKenSXKrqnfTudaRnsPMFQXPQ ae+Iq9kecL40EJmZx03IkKwsxZ1dqfr4h0K9cQRa+mj5Xg+1TXfTXfcsaDLiqZeg a1sQbf3ZbKYz88yJmRp2UrbJMGkqjnuwvvD2MkLtxqTS2pIl/sUGx/ltZDu592uU dfOddTVrqV/MBj0YtLFpU4cFY/4pdIkqP01sN61Bbn+jvYFcceA= =8yPm -----END PGP SIGNATURE----- --nfbiwxgfuwekt25w--