mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2026-06-08 06:20:14 -04:00
d693534513
After a recent fsmark benchmarking run, I observed that the overhead of
parent pointers on file creation and deletion can be a bit high. On a
machine with 20 CPUs, 128G of memory, and an NVME SSD capable of pushing
750000iops, I see the following results:
$ mkfs.xfs -f -l logdev=/dev/nvme1n1,size=1g /dev/nvme0n1 -n parent=0
meta-data=/dev/nvme0n1 isize=512 agcount=40, agsize=9767586 blks
= sectsz=4096 attr=2, projid32bit=1
= crc=1 finobt=1, sparse=1, rmapbt=1
= reflink=1 bigtime=1 inobtcount=1 nrext64=1
= exchange=0 metadir=0
data = bsize=4096 blocks=390703440, imaxpct=5
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0, ftype=1, parent=0
log =/dev/nvme1n1 bsize=4096 blocks=262144, version=2
= sectsz=4096 sunit=1 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
= rgcount=0 rgsize=0 extents
= zoned=0 start=0 reserved=0
So we created 40 AGs, one per CPU. Now we create 40 directories and run
fsmark:
$ time fs_mark -D 10000 -S 0 -n 100000 -s 0 -L 8 -d ...
# Version 3.3, 40 thread(s) starting at Wed Dec 10 14:22:07 2025
# Sync method: NO SYNC: Test does not issue sync() or fsync() calls.
# Directories: Time based hash between directories across 10000 subdirectories with 180 seconds per subdirectory.
# File names: 40 bytes long, (16 initial bytes of time stamp with 24 random bytes at end of name)
# Files info: size 0 bytes, written with an IO size of 16384 bytes per write
# App overhead is time in microseconds spent in the test not doing file writing related system calls.
parent=0 parent=1
================== ==================
real 0m57.573s real 1m2.934s
user 3m53.578s user 3m53.508s
sys 19m44.440s sys 25m14.810s
$ time rm -rf ...
parent=0 parent=1
================== ==================
real 0m59.649s real 1m12.505s
user 0m41.196s user 0m47.489s
sys 13m9.566s sys 20m33.844s
Parent pointers increase the system time by 28% overhead to create 32
million files that are totally empty. Removing them incurs a system
time increase of 56%. Wall time increases by 9% and 22%.
For most filesystems, each file tends to have a single owner and not
that many xattrs. If the xattr structure is shortform, then all xattr
changes are logged with the inode and do not require the the xattr
intent mechanism to persist the parent pointer.
Therefore, we can speed up parent pointer operations by calling the
shortform xattr functions directly if the child's xattr is in short
format. Now the overhead looks like:
$ time fs_mark -D 10000 -S 0 -n 100000 -s 0 -L 8 -d ...
parent=0 parent=1
================== ==================
real 0m58.030s real 1m0.983s
user 3m54.141s user 3m53.758s
sys 19m57.003s sys 21m30.605s
$ time rm -rf ...
parent=0 parent=1
================== ==================
real 0m58.911s real 1m4.420s
user 0m41.329s user 0m45.169s
sys 13m27.857s sys 15m58.564s
Now parent pointers only increase the system time by 8% for creation and
19% for deletion. Wall time increases by 5% and 9% now.
Close the performance gap by creating helpers for the attr set, remove,
and replace operations that will try to make direct shortform updates,
and fall back to the attr intent machinery if that doesn't work. This
works for regular xattrs and for parent pointers.
Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. Quick Start ----------- * Report a bug: See Documentation/admin-guide/reporting-issues.rst * Get the latest kernel: https://kernel.org * Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst * Join the community: https://lore.kernel.org/ Essential Documentation ----------------------- All users should be familiar with: * Building requirements: Documentation/process/changes.rst * Code of Conduct: Documentation/process/code-of-conduct.rst * License: See COPYING Documentation can be built with make htmldocs or viewed online at: https://www.kernel.org/doc/html/latest/ Who Are You? ============ Find your role below: * New Kernel Developer - Getting started with kernel development * Academic Researcher - Studying kernel internals and architecture * Security Expert - Hardening and vulnerability analysis * Backport/Maintenance Engineer - Maintaining stable kernels * System Administrator - Configuring and troubleshooting * Maintainer - Leading subsystems and reviewing patches * Hardware Vendor - Writing drivers for new hardware * Distribution Maintainer - Packaging kernels for distros For Specific Users ================== New Kernel Developer -------------------- Welcome! Start your kernel development journey here: * Getting Started: Documentation/process/development-process.rst * Your First Patch: Documentation/process/submitting-patches.rst * Coding Style: Documentation/process/coding-style.rst * Build System: Documentation/kbuild/index.rst * Development Tools: Documentation/dev-tools/index.rst * Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst * Core APIs: Documentation/core-api/index.rst Academic Researcher ------------------- Explore the kernel's architecture and internals: * Researcher Guidelines: Documentation/process/researcher-guidelines.rst * Memory Management: Documentation/mm/index.rst * Scheduler: Documentation/scheduler/index.rst * Networking Stack: Documentation/networking/index.rst * Filesystems: Documentation/filesystems/index.rst * RCU (Read-Copy Update): Documentation/RCU/index.rst * Locking Primitives: Documentation/locking/index.rst * Power Management: Documentation/power/index.rst Security Expert --------------- Security documentation and hardening guides: * Security Documentation: Documentation/security/index.rst * LSM Development: Documentation/security/lsm-development.rst * Self Protection: Documentation/security/self-protection.rst * Reporting Vulnerabilities: Documentation/process/security-bugs.rst * CVE Procedures: Documentation/process/cve.rst * Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst * Security Features: Documentation/userspace-api/seccomp_filter.rst Backport/Maintenance Engineer ----------------------------- Maintain and stabilize kernel versions: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * Backporting Guide: Documentation/process/backporting.rst * Applying Patches: Documentation/process/applying-patches.rst * Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git for Maintainers: Documentation/maintainer/configure-git.rst System Administrator -------------------- Configure, tune, and troubleshoot Linux systems: * Admin Guide: Documentation/admin-guide/index.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst * Tracing/Debugging: Documentation/trace/index.rst * Performance Security: Documentation/admin-guide/perf-security.rst * Hardware Monitoring: Documentation/hwmon/index.rst Maintainer ---------- Lead kernel subsystems and manage contributions: * Maintainer Handbook: Documentation/maintainer/index.rst * Pull Requests: Documentation/maintainer/pull-requests.rst * Managing Patches: Documentation/maintainer/modifying-patches.rst * Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst * Development Process: Documentation/process/maintainer-handbooks.rst * Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git Configuration: Documentation/maintainer/configure-git.rst Hardware Vendor --------------- Write drivers and support new hardware: * Driver API Guide: Documentation/driver-api/index.rst * Driver Model: Documentation/driver-api/driver-model/driver.rst * Device Drivers: Documentation/driver-api/infrastructure.rst * Bus Types: Documentation/driver-api/driver-model/bus.rst * Device Tree Bindings: Documentation/devicetree/bindings/ * Power Management: Documentation/driver-api/pm/index.rst * DMA API: Documentation/core-api/dma-api.rst Distribution Maintainer ----------------------- Package and distribute the kernel: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * ABI Documentation: Documentation/ABI/README * Kernel Configuration: Documentation/kbuild/kconfig.rst * Module Signing: Documentation/admin-guide/module-signing.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst Communication and Support ========================= * Mailing Lists: https://lore.kernel.org/ * IRC: #kernelnewbies on irc.oftc.net * Bugzilla: https://bugzilla.kernel.org/ * MAINTAINERS file: Lists subsystem maintainers and mailing lists * Email Clients: Documentation/process/email-clients.rst