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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Marek Szyprowski , Robin Murphy , Sumit Semwal , Benjamin Gaignard , Brian Starkey , John Stultz , "T.J. Mercier" , Christian =?utf-8?B?S8O2bmln?= , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Catalin Marinas , Will Deacon , Chun Ng , Thierry Reding , devicetree@vger.kernel.org, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-s390@vger.kernel.org, linux-mm@kvack.org, iommu@lists.linux.dev, linaro-mm-sig@lists.linaro.org, linux-trace-kernel@vger.kernel.org, Thierry Reding Subject: Re: [PATCH v4 05/10] mm/cma: Allow dynamically creating CMA areas Message-ID: References: <20260807-tegra-vpr-v4-0-5510d16af89e@nvidia.com> <20260807-tegra-vpr-v4-5-5510d16af89e@nvidia.com> <3b458c02-e836-4b24-a712-57fa8dd59e45@kernel.org> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="i7x3s4iklpcr3dcx" Content-Disposition: inline In-Reply-To: <3b458c02-e836-4b24-a712-57fa8dd59e45@kernel.org> X-Rspamd-Queue-Id: D019816000F X-Rspamd-Server: rspam10 X-Rspam-User: X-Stat-Signature: rxfti37kntnn9xxixpu6tquy6grrd3y6 X-HE-Tag: 1786371258-615010 X-HE-Meta: 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 c36TFcS4 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: --i7x3s4iklpcr3dcx Content-Type: text/plain; protected-headers=v1; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Subject: Re: [PATCH v4 05/10] mm/cma: Allow dynamically creating CMA areas MIME-Version: 1.0 On Fri, Aug 07, 2026 at 06:16:06PM +0200, David Hildenbrand (Arm) wrote: > On 8/7/26 17:54, 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 > > --- >=20 > Sorry that I didn't get to reply earlier to >=20 > https://lore.kernel.org/all/anS0nxAwCXGWZRl9@orome/ >=20 > But I am still not convinced why we shouldn't just have a single array th= at > grows dynamically. >=20 > " > After replying to T.J. I think this static array is actually a nice > feature in a way. It allows us to more easily make a distinction between > the regular CMA regions created from reserved-memory regions that > represent classic carveouts, and the more versatile CMA areas that could > be used for any purpose. >=20 > Telling the two types apart could obviously also be solved using some > kind of flag stored with the CMA area, but at this point I don't really > see a reason why the two lists would need to be unified. > " >=20 > Really, cma_for_each_early_area() + cma_for_each_area() is just nasty. >=20 > I'd strongly vote to unify unless there is a very good reason to do it > separately. Marek had an interesting suggestion to extend CMA with fixed address or range allocations, in which case we would only need a single CMA area. If that works and is acceptable, there's not much need any longer for cma_create()/cma_free(). 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