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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 Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Richard Henderson , David Hildenbrand , Matt Turner , Albert Ou , Michal Simek , Russell King , Ivan Kokshaysky , linux-riscv@lists.infradead.org, Alexander Gordeev , Dave Hansen , Jonas Bonn , Will Deacon , "James E . J . Bottomley" , "H . Peter Anvin" , Andrea Arcangeli , openrisc@lists.librecores.org, linux-s390@vger.kernel.org, Ingo Molnar , linux-m68k@lists.linux-m68k.org, Palmer Dabbelt , Heiko Carstens , Chris Zankel , Peter Zijlstra , Alistair Popple , linux-csky@vger.kernel.org, linux-hexagon@vger.kernel.org, Vlastimil Babka , Thomas Gleixner , sparclinux@vger.kernel.org, Christian Borntraeger , Stafford Horne , Michael Ellerman , x86@kernel.org, Thomas Bogendoerfer , Paul Mackerras , linux-arm-kernel@lists.infradead.org, Sven Schnelle , Benjamin Herrenschmidt , linux-xtensa@linux-xtensa.org, Nicholas Piggin , linux-sh@vger.kernel.org, Vasily Gorbik , Borislav Petkov , linux-mips@vger.kernel.org, Max Filippov , Helge Deller , Vineet Gupta , Al Viro , Paul Walmsley , Johannes Weiner , Anton Ivanov , Catalin Marinas , linux-um@lists.infradead.org, linux-alpha@vger.kernel.org, Johannes Berg , linux-ia64@vger.kernel.org, Geert Uytterhoeven , Dinh Nguyen , Guo Ren , linux-snps-arc@lists.infradead.org, Hugh Dickins , Rich Felker , Andy Lutomirski , Richard Weinberger , linuxppc-dev@lists.ozlabs.org, Brian Cain , Yoshinori Sato , Andrew Morton , Stefan Kristiansson , linux-parisc@vger.kernel.org, "David S . Miller" 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-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 99815180040 X-Stat-Signature: ycige5yoodded475buhr9rn9xbgtq4yg X-Rspam-User: Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=nXTl96gp; spf=pass (imf24.hostedemail.com: domain of mingo.kernel.org@gmail.com designates 209.85.218.50 as permitted sender) smtp.mailfrom=mingo.kernel.org@gmail.com; dmarc=fail reason="SPF not aligned (relaxed), DKIM not aligned (relaxed)" header.from=kernel.org (policy=none) X-HE-Tag: 1653648383-198686 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: * 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