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Thu, 07 May 2020 10:25:19 -0700 (PDT) Subject: Re: [PATCH 1/2] ARM: Remove redundant ARCH_SPARSEMEM_DEFAULT setting To: Russell King - ARM Linux admin References: <20200506235009.25023-1-f.fainelli@gmail.com> <20200506235009.25023-2-f.fainelli@gmail.com> <20200507103039.GR1551@shell.armlinux.org.uk> From: Florian Fainelli Message-ID: <3e7ee3ba-fae9-0ec3-fe1f-c076fc28aba9@gmail.com> Date: Thu, 7 May 2020 10:25:16 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Firefox/68.0 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200507103039.GR1551@shell.armlinux.org.uk> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200507_102523_043216_FCF37D92 X-CRM114-Status: GOOD ( 19.50 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Doug Berger , Arnd Bergmann , sboyd@kernel.org, Kevin Cernekee , Mike Rapoport , Gregory Fong , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 5/7/2020 3:30 AM, Russell King - ARM Linux admin wrote: > On Wed, May 06, 2020 at 04:50:08PM -0700, Florian Fainelli wrote: >> From: Kevin Cernekee >> >> If ARCH_SPARSEMEM_ENABLE=y and ARCH_{FLATMEM,DISCONTIGMEM}_ENABLE=n, >> then the logic in mm/Kconfig already makes CONFIG_SPARSEMEM the only >> choice. This is true for all of the existing ARM users of >> ARCH_SPARSEMEM_ENABLE. >> >> Forcing ARCH_SPARSEMEM_DEFAULT=y if ARCH_SPARSEMEM_ENABLE=y prevents >> us from ever defaulting to FLATMEM, so we should remove this setting. > > No explanation why that is desirable. This was explained in the original submission out of which only the first patch landed upstream: https://lkml.org/lkml/2015/6/4/756 > >> -config ARCH_SPARSEMEM_DEFAULT >> - def_bool ARCH_SPARSEMEM_ENABLE >> - > > What this basically says is ARCH_SPARSEMEM_ENABLE=ARCH_SPARSEMEM_DEFAULT, > which is exactly what we want for the non-multiplatform boards that > select ARCH_SPARSEMEM_ENABLE - we _want_ them to default to sparsemem > because that is what the platform requires. > > For example, with RiscPC, which selects ARCH_SPARSEMEM_ENABLE, we have > four banks of memory at 0x10000000, 0x14000000, 0x18000000 and > 0x1c000000. These correspond with the two memory slots - the first two > for the first slot, and the second two for the second slot. Each slot > has two banks. The size of each memory bank depends on the size of the > module. > > Flatmem is completely unable to work with this setup if all banks are > populated, and the first bank does not contain enough memory to allocate > the struct page array. So, sparsemem is the only option there. > > Hence, for these platforms, we want sparsemem and only sparsemem, not > flatmem. > > So, this patch which makes it possible to select flatmem is completely > out of the question for these platforms. OK. -- Florian _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel