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[47.72.206.164]) by smtp.gmail.com with ESMTPSA id d16-20020a170902b71000b0016a7b9558f7sm26513101pls.136.2022.07.08.00.00.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 08 Jul 2022 00:00:24 -0700 (PDT) From: Barry Song <21cnbao@gmail.com> To: namit@vmware.com Cc: 21cnbao@gmail.com, akpm@linux-foundation.org, arnd@arndb.de, catalin.marinas@arm.com, corbet@lwn.net, darren@os.amperecomputing.com, guojian@oppo.com, huzhanyuan@oppo.com, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lipeifeng@oppo.com, mgorman@suse.de, realmz6@gmail.com, v-songbaohua@oppo.com, will@kernel.org, x86@kernel.org, yangyicong@hisilicon.com, zhangshiming@oppo.com Subject: Re: [PATCH 2/4] mm: rmap: Allow platforms without mm_cpumask to defer TLB flush Date: Fri, 8 Jul 2022 18:59:57 +1200 Message-Id: <20220708065957.3859-1-21cnbao@gmail.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <67943544-6DAA-4C8A-A04D-029D2D36C318@vmware.com> References: <67943544-6DAA-4C8A-A04D-029D2D36C318@vmware.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > The cpumask_empty() is indeed just another memory access, which is most > likely ok. But wouldn’t adding something like CONFIG_ARCH_HAS_MM_CPUMASK > make the code simpler and (slightly, certainly slightly) more performant? Yep. good suggestion, Nadav. So the code will be as below, right? diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index be0b95e51df6..a91d73866238 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -81,6 +81,7 @@ config X86 select ARCH_HAS_KCOV if X86_64 select ARCH_HAS_MEM_ENCRYPT select ARCH_HAS_MEMBARRIER_SYNC_CORE + select ARCH_HAS_MM_CPUMASK select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE select ARCH_HAS_PMEM_API if X86_64 select ARCH_HAS_PTE_DEVMAP if X86_64 diff --git a/mm/Kconfig b/mm/Kconfig index 169e64192e48..7bf54f57ca01 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -951,6 +951,9 @@ config ARCH_HAS_CURRENT_STACK_POINTER register alias named "current_stack_pointer", this config can be selected. +config ARCH_HAS_MM_CPUMASK + bool + config ARCH_HAS_VM_GET_PAGE_PROT bool diff --git a/mm/rmap.c b/mm/rmap.c index 5bcb334cd6f2..13d4f9a1d4f1 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -692,6 +692,10 @@ static bool should_defer_flush(struct mm_struct *mm, enum ttu_flags flags) if (!(flags & TTU_BATCH_FLUSH)) return false; +#ifndef CONFIG_ARCH_HAS_MM_CPUMASK + return true; +#endif + /* If remote CPUs need to be flushed then defer batch the flush */ if (cpumask_any_but(mm_cpumask(mm), get_cpu()) < nr_cpu_ids) should_defer = true; Thanks Barry