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In-Reply-To: From: Arnd Bergmann Date: Wed, 22 Jul 2020 22:22:25 +0200 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v5 1/4] riscv: Move kernel mapping to vmalloc zone To: Palmer Dabbelt Content-Type: text/plain; charset="UTF-8" X-Provags-ID: V03:K1:igSlMCHB8qHw5Fcfti+sLl7kHvxbFweWd/QG3taVeuXAXJUf+JQ XoZ7a86ZOFYmJubi5TYCcsF2Yjv2+MXzMnZHxc30LEuvQN760T0l11l775YMnAjlfQX69p/ ClWiBvEXoKNC95nwJ8fFLXd3geqSZOSWIvn1O8sCwXcjGNhEQr1tRchyxgvkTVPETpibDtF s2qRgYQSPYWR77fwHdT6A== X-UI-Out-Filterresults: notjunk:1;V03:K0:NI5uOhR3Xjk=:r9rqVHc9+px0ggzsSkg12t LvnqoJgTdYJ6hkdNbAc8xyzY6hpmwSyhYHy12f+Sa4VtjevxWXznoZQsf94CApRsvLnGFO0TZ x/c0WMCeGORs4+eXB+96kOMuxUKC5njAmx1pIsroMCquBZjXqhXUGAajhRRCYkX0XGeDCu1Dy Q+urR/h2JDGp8ZH+n/PO+/dBrYFtA+EFJkZz+/BlhOh3gHqSbAyD+RzMrIQ3FX7ixGD5dvTNT stR2fqwZPC5lV1dgR8ONb5kPcQnbJrhy/9Cq+sprGjGjstOvs+LFyCJt0z+xgmhvtGLdW/w3T oEXfmEmsjGqCf6t1tK1XScx83x3YZnT0rhUNL3QiRLHYXAjdZK8l7up4fiD1J62wvEMordJIK HubxIj8anvKaVfr9MUFAQb7WIpOeIYi4ttc6Iob+DkbYsDOFGe7FY0bqsB0piXjlL6J5dYSva geolKG+R7Gc0OUn1oldUEzQiswTZYRroD+s7Gh2sMyr0rQB4KgCIm70utoV7oM0M2YszQiXX1 ZBmpPaXtlaoBdLWZg0mZw7srocflgaKIhyPdKF+dBb+WHq+hfHJauVdp0sHouvKkgJ76kp6CM yhCApCJTEzH1hqi3axQ1+A9fy5Hup7m6fQug3oibp4DqA+be0zCaDxLFEcN3oIKmDNAuXSE1v 223ABt8qAeJG1F5BowfjQqp7xzMKFURYO/fZT6G3Uy8TrC+gmNUEnAM7EmimmckUA4bDFkdgk 2aTjsug4i2218ifFLGaQU/Y8ttlGGHAroijp7baGGJTLkgpSbq6ATNTlyPM+6C1yholq0ryY9 gbPOLTzqwjEktzI3z0EkgrJXIx/SpkS+YfM2u/ubppPrFKEQWVnIog2g7cF5KNolEfTjSxK X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Albert Ou , Alexandre Ghiti , Atish Patra , Anup Patel , "linux-kernel@vger.kernel.org" , Paul Walmsley , Linux-MM , Paul Mackerras , Zong Li , linux-riscv , linuxppc-dev Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Wed, Jul 22, 2020 at 9:52 PM Palmer Dabbelt wrote: > On Wed, 22 Jul 2020 02:43:50 PDT (-0700), Arnd Bergmann wrote: > > On Tue, Jul 21, 2020 at 9:06 PM Palmer Dabbelt wrote: > > The eventual goal is to have a split of 3840MB for either user or linear map > > plus and 256MB for vmalloc, including the kernel. Switching between linear > > and user has a noticeable runtime overhead, but it relaxes both the limits > > for user memory and lowmem, and it provides a somewhat stronger > > address space isolation. > > Ya, I think we decided not to do that, at least for now. I guess the right > answer there will depend on what 32-bit systems look like, and since we don't > have any I'm inclined to just stick to the fast option. Makes sense. Actually on 32-bit Arm we see fewer large-memory configurations in new machines than we had in the past before 64-bit machines were widely available at low cost, so I expect not to see a lot new hardware with more than 1GB of DDR3 (two 256Mbit x16 chips) for cost reasons, and rv32 is likely going to be similar, so you may never really see a need for highmem or the above hack to increase the size of the linear mapping. I just noticed that rv32 allows 2GB of lowmem rather than just the usual 768MB or 1GB, at the expense of addressable user memory. This seems like an unusual choice, but I also don't see any reason to change this or make it more flexible unless actual users appear. Arnd