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[86.59.161.111]) by smtp.gmail.com with ESMTPSA id i20-20020a17090639d400b006fec1a73e48sm1320742eje.64.2022.05.27.03.46.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 27 May 2022 03:46:34 -0700 (PDT) Date: Fri, 27 May 2022 12:46:31 +0200 From: Ingo Molnar To: Peter Xu Subject: Re: [PATCH v3] mm: Avoid unnecessary page fault retires on shared memory types Message-ID: References: <20220524234531.1949-1-peterx@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220524234531.1949-1-peterx@redhat.com> X-Mailman-Approved-At: Fri, 27 May 2022 21:29:50 +1000 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: x86@kernel.org, Catalin Marinas , David Hildenbrand , Peter Zijlstra , Dave Hansen , linux-mips@vger.kernel.org, "James E . J . 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Peter Anvin" , sparclinux@vger.kernel.org, linux-ia64@vger.kernel.org, Alexander Gordeev , Will Deacon , linux-riscv@lists.infradead.org, Anton Ivanov , Jonas Bonn , linux-s390@vger.kernel.org, linux-snps-arc@lists.infradead.org, Yoshinori Sato , linux-xtensa@linux-xtensa.org, linux-hexagon@vger.kernel.org, Helge Deller , Alistair Popple , Hugh Dickins , Russell King , linux-csky@vger.kernel.org, linux-sh@vger.ke rnel.org, Ingo Molnar , Geert Uytterhoeven , linux-arm-kernel@lists.infradead.org, Vineet Gupta , Stafford Horne , Matt Turner , Christian Borntraeger , Andrea Arcangeli , Albert Ou , Vasily Gorbik , Brian Cain , Heiko Carstens , Johannes Weiner , linux-um@lists.infradead.org, Nicholas Piggin , Stefan Kristiansson , Richard Weinberger , linux-m68k@lists.linux-m68k.org, openrisc@lists.librecores.org, Ivan Kokshaysky , Al Viro , Andy Lutomirski , Paul Walmsley , Thomas Gleixner , linux-alpha@vger.kernel.org, Andrew Morton , Vlastimil Bab ka , Richard Henderson , Chris Zankel , Michal Simek , Thomas Bogendoerfer , linux-parisc@vger.kernel.org, Max Filippov , linux-kernel@vger.kernel.org, Dinh Nguyen , Palmer Dabbelt , Sven Schnelle , Guo Ren , Borislav Petkov , Johannes Berg , linuxppc-dev@lists.ozlabs.org, "David S . Miller" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" * Peter Xu wrote: > This patch provides a ~12% perf boost on my aarch64 test VM with a simple > program sequentially dirtying 400MB shmem file being mmap()ed and these are > the time it needs: > > Before: 650.980 ms (+-1.94%) > After: 569.396 ms (+-1.38%) Nice! > arch/x86/mm/fault.c | 4 ++++ Reviewed-by: Ingo Molnar Minor comment typo: > + /* > + * We should do the same as VM_FAULT_RETRY, but let's not > + * return -EBUSY since that's not reflecting the reality on > + * what has happened - we've just fully completed a page > + * fault, with the mmap lock released. Use -EAGAIN to show > + * that we want to take the mmap lock _again_. > + */ s/reflecting the reality on what has happened /reflecting the reality of what has happened > ret = handle_mm_fault(vma, address, fault_flags, NULL); > + > + if (ret & VM_FAULT_COMPLETED) { > + /* > + * NOTE: it's a pity that we need to retake the lock here > + * to pair with the unlock() in the callers. Ideally we > + * could tell the callers so they do not need to unlock. > + */ > + mmap_read_lock(mm); > + *unlocked = true; > + return 0; Indeed that's a pity - I guess more performance could be gained here, especially in highly parallel threaded workloads? Thanks, Ingo