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[2003:cb:c709:b600:e63:6c3b:7b5d:f439]) by smtp.gmail.com with ESMTPSA id d7-20020adfe2c7000000b002d419f661d6sm12391832wrj.82.2023.04.04.06.47.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 04 Apr 2023 06:47:58 -0700 (PDT) Message-ID: <78a31392-8f9b-9705-918a-24edb650f395@redhat.com> Date: Tue, 4 Apr 2023 15:47:56 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.1 Subject: Re: [PATCH 1/3] arch: Introduce ARCH_HAS_CPUMASK_BITS Content-Language: en-US To: Yair Podemsky , linux@armlinux.org.uk, mpe@ellerman.id.au, npiggin@gmail.com, christophe.leroy@csgroup.eu, hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, borntraeger@linux.ibm.com, svens@linux.ibm.com, davem@davemloft.net, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, will@kernel.org, aneesh.kumar@linux.ibm.com, akpm@linux-foundation.org, peterz@infradead.org, arnd@arndb.de, keescook@chromium.org, paulmck@kernel.org, jpoimboe@kernel.org, samitolvanen@google.com, frederic@kernel.org, ardb@kernel.org, juerg.haefliger@canonical.com, rmk+kernel@armlinux.org.uk, geert+renesas@glider.be, tony@atomide.com, linus.walleij@linaro.org, sebastian.reichel@collabora.com, nick.hawkins@hpe.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, mtosatti@redhat.com, vschneid@redhat.com, dhildenb@redhat.com Cc: alougovs@redhat.com References: <20230404134224.137038-1-ypodemsk@redhat.com> <20230404134224.137038-2-ypodemsk@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20230404134224.137038-2-ypodemsk@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On 04.04.23 15:42, Yair Podemsky wrote: > Some architectures set and maintain the mm_cpumask bits when loading > or removing process from cpu. > This Kconfig will mark those to allow different behavior between > kernels that maintain the mm_cpumask and those that do not. > I was wondering if we should do something along the lines of: diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 0722859c3647..1f5c15d8e8ed 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -767,11 +767,13 @@ struct mm_struct { #endif /* CONFIG_LRU_GEN */ } __randomize_layout; +#ifdef CONFIG_MM_CPUMASK /* * The mm_cpumask needs to be at the end of mm_struct, because it * is dynamically sized based on nr_cpu_ids. */ unsigned long cpu_bitmap[]; +#endif }; But that would, of course, require additional changes to make it compile. What concerns me a bit is that we have in mm/rmap.c a mm_cpumask() usage. But it's glued to CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH ... shaky. At least if we would properly fence it, there would be no accidental abuse anymore. > Signed-off-by: Yair Podemsky > --- > arch/Kconfig | 8 ++++++++ > arch/arm/Kconfig | 1 + > arch/powerpc/Kconfig | 1 + > arch/s390/Kconfig | 1 + > arch/sparc/Kconfig | 1 + > arch/x86/Kconfig | 1 + As Valentin says, there are other architectures that do the same. -- Thanks, David / dhildenb