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Mon, 13 Apr 2026 07:15:29 -0400 (EDT) X-Mailer: MessagingEngine.com Webmail Interface Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-ThreadId: Ax9AE_gslVNw Date: Mon, 13 Apr 2026 13:14:49 +0200 From: "Arnd Bergmann" To: "Mike Rapoport" , linux-sh@vger.kernel.org Cc: "Andrew Morton" , "John Paul Adrian Glaubitz" , "Rich Felker" , "Yoshinori Sato" , linux-kernel@vger.kernel.org, linux-mm@kvack.org Message-Id: <42a4c6c1-762f-449f-9d14-3eb0fa02b94f@app.fastmail.com> In-Reply-To: <20260413104649.852228-1-rppt@kernel.org> References: <20260413104649.852228-1-rppt@kernel.org> Subject: Re: [PATCH 00/10] sh: remove NUMA and SPARSEMEM support Content-Type: text/plain Content-Transfer-Encoding: 7bit On Mon, Apr 13, 2026, at 12:46, Mike Rapoport wrote: > > NUMA support for SuperH was introduced a long time ago by commit > b241cb0c885e ("sh: Support for multiple nodes.") > > "... for boards with many different memory blocks that are > otherwise unused (SH7722/SH7785 URAM and so forth)" > > In reality, this added 128K of memory on sh7722 and sh7785 and 256K on > shx3 at the expense of all the NUMA related code in the kernel. > > For build of v7.0-rc7 with defconfig and the same configuration with > CONFIG_NUMA disabled, bloat-o-meter reports difference of ~76k. Disabling > CONFIG_SPARSMEM on top increases the difference to ~94k. And that's only > overhead in code and static data that does not take into the account data > structures allocated at run time. > > And all this overhead has been there for nothing for almost 8 years > because since commit ac21fc2dcb40 ("sh: switch to NO_BOOTMEM") > those additional "nodes" could not be used by the core MM because the > maximal pfn for ZONE_NORMAL was cut out at the end of the normal memory. I had looked at it when you asked me about it last year, and I can confirm that agree with all your findings and the resulting patches. Whole series Reviewed-by: Arnd Bergmann Two very minor points: * It looks like you left the 'config SYS_SUPPORTS_NUMA' symbol in Kconfig, which no longer does anything, so this should probably be removed in patch 9 along with the lines that select it. * It appears that after your series, RISC-V is the only remaining architecture that supports NUMA in 32-bit mode, which I think we should not allow as a configuration, given that this would run into untested code and no hardware exists for it. Apparently commit 4f0e8eef772e ("riscv: Add numa support for riscv64 platform") intended this to only be for 64-bit targets but did not add a Kconfig dependency for CONFIG_64BIT (or CONFIG_SMP, which was added later). Arnd