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McIFPfL9WMlxQJaI10SsxqFq8Yvr4VddZIP1dqA2uwZUWMweg4XqNY6NrMsPIORwJ5SN4Vr4vHa/4BYTfIjMTZOicQFNnPufbZjtQg6YTAXYBjuQYD50DKSs/m7lrvmMkQGp4CA/UGbHHGiAxmUL0B+9hctV8C52BLr8wJZgC8fe1bMhQdtS0JAt1RTOcrUn4RVpa+eIZ6C0j9SkeqPiJbr2rvAO32aDvn8dwa0YKGzadYilfrqNKNCZtjIB7sVx44kwqCtNluxLZfh1TQ/DEPTwRFvRYsr0HZEEMFZbm1nf4bfso+gFc7xkw9D9de5g 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: List-Subscribe: List-Unsubscribe: On 11/27/2025 9:14 AM, Barry Song wrote: > > From: Barry Song > > Oven observed most mmap_lock contention and priority inversion > come from page fault retries after waiting for I/O completion. > Oven subsequently raised the following idea: > > There is no need to always fall back to mmap_lock if the per-VMA > lock was released only to wait for pagecache or swapcache to > become ready. > > In this case, the retry path can continue using the per-VMA lock. > This is a big win: it greatly reduces mmap_lock acquisitions. Here are some test data for the patches: == Test Case == Douyin (Chinese version of TikTok) warm start on smart phone with 8GB RAM == mmap_lock Acquisitions And Wait Time == Metric Before (Avg) After (Avg) Change ------------------------------------------------------------------------ Read Lock Count 20,010 5,719 -71.42% Read Total Wait (us) 10,695,877 408,436 -96.18% Read Avg Wait (us) 534.00 71.00 -86.70% Write Lock Count 838 909 +8.47% Write Total Wait (us) 501,293 97,633 -80.52% Write Avg Wait (us) 598.00 107.00 -82.11% == Read Lock Waiting Time Distribution of mmap_lock == Range (us) Before (Avg) After (Avg) Change ------------------------------------------------------------------------ [0, 1) 9,927 4,286 -56.82% [1, 10) 9,179 1,327 -85.54% [10, 100) 191 88 -53.93% [100, 1000) 57 6 -89.47% [1000, 10000) 328 9 -97.26% [10000, 100000) 328 6 -98.17% [100000, 1000000) 0 0 N/A [1000000, +) 0 0 N/A == Write Lock Waiting Time Distribution of mmap_lock == Range (us) Before (Avg) After (Avg) Change ------------------------------------------------------------------------ [0, 1) 250 300 +20.00% [1, 10) 483 556 +15.11% [10, 100) 52 41 -21.15% [100, 1000) 12 5 -58.33% [1000, 10000) 22 4 -81.82% [10000, 100000) 16 1 -93.75% [100000, 1000000) 0 0 N/A [1000000, +) 0 0 N/A After the optimization, the number of read lock acquisitions is significantly reduced, and both lock waiting time and tail latency are dramatically improved. Thanks, Oven > > Oven Liyang (1): > mm/filemap: Retry fault by VMA lock if the lock was released for I/O > > Barry Song (1): > mm/swapin: Retry swapin by VMA lock if the lock was released for I/O > > arch/arm/mm/fault.c | 5 +++++ > arch/arm64/mm/fault.c | 5 +++++ > arch/loongarch/mm/fault.c | 4 ++++ > arch/powerpc/mm/fault.c | 5 ++++- > arch/riscv/mm/fault.c | 4 ++++ > arch/s390/mm/fault.c | 4 ++++ > arch/x86/mm/fault.c | 4 ++++ > include/linux/mm_types.h | 9 +++++---- > mm/filemap.c | 5 ++++- > mm/memory.c | 10 ++++++++-- > 10 files changed, 47 insertions(+), 8 deletions(-) > > Cc: Russell King > Cc: Catalin Marinas > Cc: Will Deacon > Cc: Huacai Chen > Cc: WANG Xuerui > Cc: Madhavan Srinivasan > Cc: Michael Ellerman > Cc: Nicholas Piggin > Cc: Christophe Leroy > Cc: Paul Walmsley > Cc: Palmer Dabbelt > Cc: Albert Ou > Cc: Alexandre Ghiti > Cc: Alexander Gordeev > Cc: Gerald Schaefer > Cc: Heiko Carstens > Cc: Vasily Gorbik > Cc: Christian Borntraeger > Cc: Sven Schnelle > Cc: Dave Hansen > Cc: Andy Lutomirski > Cc: Peter Zijlstra > Cc: Thomas Gleixner > Cc: Ingo Molnar > Cc: Borislav Petkov > Cc: x86@kernel.org > Cc: H. Peter Anvin > Cc: David Hildenbrand > Cc: Lorenzo Stoakes > Cc: Liam R. Howlett > Cc: Vlastimil Babka > Cc: Mike Rapoport > Cc: Suren Baghdasaryan > Cc: Michal Hocko > Cc: Matthew Wilcox > Cc: Pedro Falcato > Cc: Jarkko Sakkinen > Cc: Oscar Salvador > Cc: Kuninori Morimoto > Cc: Oven Liyang > Cc: Mark Rutland > Cc: Ada Couprie Diaz > Cc: Robin Murphy > Cc: Kristina Martšenko > Cc: Kevin Brodsky > Cc: Yeoreum Yun > Cc: Wentao Guan > Cc: Thorsten Blum > Cc: Steven Rostedt > Cc: Yunhui Cui > Cc: Nam Cao > Cc: Chris Li > Cc: Kairui Song > Cc: Kemeng Shi > Cc: Nhat Pham > Cc: Baoquan He > Cc: linux-arm-kernel@lists.infradead.org > Cc: linux-kernel@vger.kernel.org > Cc: loongarch@lists.linux.dev > Cc: linuxppc-dev@lists.ozlabs.org > Cc: linux-riscv@lists.infradead.org > Cc: linux-s390@vger.kernel.org > Cc: linux-mm@kvack.org > Cc: linux-fsdevel@vger.kernel.org > > -- > 2.39.3 (Apple Git-146) >