[RFC PATCH 0/2] mm: continue using per-VMA lock when retrying page faults after I/O
Oven Liyang
liyangouwen1 at oppo.com
Sun Jan 4 01:16:24 PST 2026
On 11/27/2025 9:14 AM, Barry Song wrote:
>
> From: Barry Song <v-songbaohua at oppo.com>
>
> 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 <linux at armlinux.org.uk>
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Will Deacon <will at kernel.org>
> Cc: Huacai Chen <chenhuacai at kernel.org>
> Cc: WANG Xuerui <kernel at xen0n.name>
> Cc: Madhavan Srinivasan <maddy at linux.ibm.com>
> Cc: Michael Ellerman <mpe at ellerman.id.au>
> Cc: Nicholas Piggin <npiggin at gmail.com>
> Cc: Christophe Leroy <christophe.leroy at csgroup.eu>
> Cc: Paul Walmsley <pjw at kernel.org>
> Cc: Palmer Dabbelt <palmer at dabbelt.com>
> Cc: Albert Ou <aou at eecs.berkeley.edu>
> Cc: Alexandre Ghiti <alex at ghiti.fr>
> Cc: Alexander Gordeev <agordeev at linux.ibm.com>
> Cc: Gerald Schaefer <gerald.schaefer at linux.ibm.com>
> Cc: Heiko Carstens <hca at linux.ibm.com>
> Cc: Vasily Gorbik <gor at linux.ibm.com>
> Cc: Christian Borntraeger <borntraeger at linux.ibm.com>
> Cc: Sven Schnelle <svens at linux.ibm.com>
> Cc: Dave Hansen <dave.hansen at linux.intel.com>
> Cc: Andy Lutomirski <luto at kernel.org>
> Cc: Peter Zijlstra <peterz at infradead.org>
> Cc: Thomas Gleixner <tglx at linutronix.de>
> Cc: Ingo Molnar <mingo at redhat.com>
> Cc: Borislav Petkov <bp at alien8.de>
> Cc: x86 at kernel.org
> Cc: H. Peter Anvin <hpa at zytor.com>
> Cc: David Hildenbrand <david at kernel.org>
> Cc: Lorenzo Stoakes <lorenzo.stoakes at oracle.com>
> Cc: Liam R. Howlett <Liam.Howlett at oracle.com>
> Cc: Vlastimil Babka <vbabka at suse.cz>
> Cc: Mike Rapoport <rppt at kernel.org>
> Cc: Suren Baghdasaryan <surenb at google.com>
> Cc: Michal Hocko <mhocko at suse.com>
> Cc: Matthew Wilcox <willy at infradead.org>
> Cc: Pedro Falcato <pfalcato at suse.de>
> Cc: Jarkko Sakkinen <jarkko at kernel.org>
> Cc: Oscar Salvador <osalvador at suse.de>
> Cc: Kuninori Morimoto <kuninori.morimoto.gx at renesas.com>
> Cc: Oven Liyang <liyangouwen1 at oppo.com>
> Cc: Mark Rutland <mark.rutland at arm.com>
> Cc: Ada Couprie Diaz <ada.coupriediaz at arm.com>
> Cc: Robin Murphy <robin.murphy at arm.com>
> Cc: Kristina Martšenko <kristina.martsenko at arm.com>
> Cc: Kevin Brodsky <kevin.brodsky at arm.com>
> Cc: Yeoreum Yun <yeoreum.yun at arm.com>
> Cc: Wentao Guan <guanwentao at uniontech.com>
> Cc: Thorsten Blum <thorsten.blum at linux.dev>
> Cc: Steven Rostedt <rostedt at goodmis.org>
> Cc: Yunhui Cui <cuiyunhui at bytedance.com>
> Cc: Nam Cao <namcao at linutronix.de>
> Cc: Chris Li <chrisl at kernel.org>
> Cc: Kairui Song <kasong at tencent.com>
> Cc: Kemeng Shi <shikemeng at huaweicloud.com>
> Cc: Nhat Pham <nphamcs at gmail.com>
> Cc: Baoquan He <bhe at redhat.com>
> Cc: linux-arm-kernel at lists.infradead.org
> Cc: linux-kernel at vger.kernel.org
> Cc: loongarch at lists.linux.dev
> Cc: linuxppc-dev at lists.ozlabs.org
> Cc: linux-riscv at lists.infradead.org
> Cc: linux-s390 at vger.kernel.org
> Cc: linux-mm at kvack.org
> Cc: linux-fsdevel at vger.kernel.org
>
> --
> 2.39.3 (Apple Git-146)
>
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