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Tue, 28 Jan 2025 09:07:12 -0800 (PST) MIME-Version: 1.0 References: <50b7265e-64b9-41a3-af48-79ded6674f21@redhat.com> In-Reply-To: <50b7265e-64b9-41a3-af48-79ded6674f21@redhat.com> From: Juan Yescas Date: Tue, 28 Jan 2025 09:07:00 -0800 X-Gm-Features: AWEUYZnz7yb3fMBZBeHYcgUwd6UlbnRjuUDeHwtpeUjWGMRd7ShlCJ4NEzD28-U Message-ID: Subject: Re: [LSF/MM/BPF TOPIC] CMA reservation optimizations To: David Hildenbrand Cc: lsf-pc@lists.linux-foundation.org, Suren Baghdasaryan , linux-mm@kvack.org, Kalesh Singh , Isaac Manjarres , "T.J. Mercier" , Zi Yan , Barry Song <21cnbao@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 3E07E80014 X-Stat-Signature: mbhxud6z38t7a3y9jwgrbq7ag8am33n5 X-Rspamd-Server: rspam08 X-Rspam-User: X-HE-Tag: 1738084033-774144 X-HE-Meta: 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 OFbm6X3w zbQP3lzEIePFLoviZhDk+QZBV8Z871eF59MUC2MuNNV6w0OjFXBa2chrow4Iimuu1nIJo3o89XVtIZYWb20bJx9iZymo4ngvrQByuz4kT80d9l514ls0quf62fHcVNCPkhb1XucMN1dTmdO7MgU9Fp3tBAV5JCtB8olSRuX2XLlchGSOUz8FFjx6rH71pQ8ZFeaU10OFF+VxHXqDM3f2aIub4Rckr9uzAKLnxM6xLNVrsWH3HLjMnT5opHDw6QNp0TOMPcfRTdRVRT61wbZAtqWn0Cw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000868, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Jan 28, 2025 at 1:58=E2=80=AFAM David Hildenbrand wrote: > > On 28.01.25 02:04, Juan Yescas wrote: > > Hi LSF organizers, > > > > I would like to continue discussing this topic with the mm community: > > > > "CMA reservation optimizations" > > > > Note: There is already an email in the linux-mm mailing list that is > > discussing this issue. The title is: > > > > "CMA reservations require 32MiB alignment in 16KiB page size kernels > > instead of 8MiB in 4KiB page size kernel" > > > > Background > > > > When the drivers reserve CMA memory in 16KiB kernels, the minimum > > alignment is 32 MiB as per CMA_MIN_ALIGNMENT_BYTES. However, in 4KiB > > kernels, the CMA alignment is 4MiB. > > I'm curious, here you say 4 MiB, above 8 MiB. > My bad, it is a typo. I meant 4 MiB. > But nowadays it's usually 2 MiB (pageblock size), no? That's right for the case when THPs are enabled in 4KiB page size configs. #define pageblock_order MIN_T(unsigned int, HPAGE_PMD_ORDER, MAX_PAGE_ORDER= ) https://elixir.bootlin.com/linux/v6.13/source/include/linux/pageblock-flags= .h#L50 This evals to pageblock_order =3D min(21 - 12, 10) =3D 9 #define CMA_MIN_ALIGNMENT_PAGES pageblock_nr_pages #define CMA_MIN_ALIGNMENT_BYTES (PAGE_SIZE * CMA_MIN_ALIGNMENT_PAGES) https://elixir.bootlin.com/linux/v6.13/source/include/linux/cma.h#L21 CMA_MIN_ALIGNMENT_BYTES =3D (4096 * 2 ^ 9) =3D (4096 * 512) =3D 2097152 =3D= 2 MiB However, when THPs are disabled, we get: #define pageblock_order MAX_PAGE_ORDER // 10 https://elixir.bootlin.com/linux/v6.13/source/arch/arm64/Kconfig#L1630 https://elixir.bootlin.com/linux/v6.13/source/include/linux/pageblock-flags= .h#L55 CMA_MIN_ALIGNMENT_BYTES =3D (4096 * 2 ^ 10) =3D (4096 * 1024) =3D 4194304 = =3D 4 MiB > > -- > Cheers, > > David / dhildenb >