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[217.213.93.172]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-5439af76fe9sm1916768e87.212.2025.01.21.09.00.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Jan 2025 09:00:12 -0800 (PST) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Tue, 21 Jan 2025 18:00:07 +0100 To: Valentin Schneider Cc: Uladzislau Rezki , Jann Horn , linux-kernel@vger.kernel.org, x86@kernel.org, virtualization@lists.linux.dev, linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linux-riscv@lists.infradead.org, linux-perf-users@vger.kernel.org, xen-devel@lists.xenproject.org, kvm@vger.kernel.org, linux-arch@vger.kernel.org, rcu@vger.kernel.org, linux-hardening@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, bpf@vger.kernel.org, bcm-kernel-feedback-list@broadcom.com, Juergen Gross , Ajay Kaher , Alexey Makhalov , Russell King , Catalin Marinas , Will Deacon , Huacai Chen , WANG Xuerui , Paul Walmsley , Palmer Dabbelt , Albert Ou , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Peter Zijlstra , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , "Liang, Kan" , Boris Ostrovsky , Josh Poimboeuf , Pawan Gupta , Sean Christopherson , Paolo Bonzini , Andy Lutomirski , Arnd Bergmann , Frederic Weisbecker , "Paul E. McKenney" , Jason Baron , Steven Rostedt , Ard Biesheuvel , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Juri Lelli , Clark Williams , Yair Podemsky , Tomas Glozar , Vincent Guittot , Dietmar Eggemann , Ben Segall , Mel Gorman , Kees Cook , Andrew Morton , Christoph Hellwig , Shuah Khan , Sami Tolvanen , Miguel Ojeda , Alice Ryhl , "Mike Rapoport (Microsoft)" , Samuel Holland , Rong Xu , Nicolas Saenz Julienne , Geert Uytterhoeven , Yosry Ahmed , "Kirill A. Shutemov" , "Masami Hiramatsu (Google)" , Jinghao Jia , Luis Chamberlain , Randy Dunlap , Tiezhu Yang Subject: Re: [PATCH v4 29/30] x86/mm, mm/vmalloc: Defer flush_tlb_kernel_range() targeting NOHZ_FULL CPUs Message-ID: References: <20250114175143.81438-1-vschneid@redhat.com> <20250114175143.81438-30-vschneid@redhat.com> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: > > > > As noted before, we defer flushing for vmalloc. We have a lazy-threshold > > which can be exposed(if you need it) over sysfs for tuning. So, we can add it. > > > > In a CPU isolation / NOHZ_FULL context, isolated CPUs will be running a > single userspace application that will never enter the kernel, unless > forced to by some interference (e.g. IPI sent from a housekeeping CPU). > > Increasing the lazy threshold would unfortunately only delay the > interference - housekeeping CPUs are free to run whatever, and so they will > eventually cause the lazy threshold to be hit and IPI all the CPUs, > including the isolated/NOHZ_FULL ones. > Do you have any testing results for your workload? I mean how much potentially we can allocate. Again, maybe it is just enough to back and once per-hour offload it. Apart of that how critical IPIing CPUs affect your workloads? > I was thinking maybe we could subdivide the vmap space into two regions > with their own thresholds, but a task may allocate/vmap stuff while on a HK > CPU and be moved to an isolated CPU afterwards, and also I still don't have > any strong guarantee about what accesses an isolated CPU can do in its > early entry code :( > I agree this is not worth to play with a vmap space in terms of splitting it. Sorry for later answer and thank you! -- Uladzislau Rezki