mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/
synced 2026-11-10 20:48:12 +00:00
No description
- C 96.8%
- Assembly 0.9%
- Rust 0.7%
- Shell 0.6%
- Python 0.5%
- Other 0.3%
41a52ba4a5
WOF decompression uses four module-global workspaces, one per compression
format, each with a static mutex. ntfs_read_wof_compressed_block() takes
that mutex once and holds it across the whole chunk loop, so both block
reads run inside it:
mutex_lock(ws->lock);
for each chunk {
parse_wof_chunk_table(..., ws->input, ...); /* reads disk */
ntfs_read_wof_chunk(..., ws->input, ...); /* reads disk */
decompress into ws->output;
}
mutex_unlock(ws->lock);
Readers of system-compressed files then serialise system-wide on the disk
waits, not just on the decompressor scratch the lock exists for. One
reader sleeping in submit_bio_wait() blocks all the rest.
The waits dominate. Reading an 8 MiB xpress4k file (2048 chunks at a 48%
compressed ratio, so 2048 acquisitions and 4096 block reads) and timing
ws->lock against the part of it spent in ntfs_bdev_read():
backing store held of that in I/O held after
virtio, host page cache 348 ms 321 ms (92%) 24.6 ms
virtio, throttled 100 MB/s 978 ms 948 ms (96%) 36.6 ms
The page-cache row is a lower bound, having no seek cost at all, and the
share still grows with slower storage because only the wait scales while
decompression stays near 26 ms.
The reads are inside the lock only because they land in ws->input, a
buffer shared through the workspace. Nothing else requires it:
parse_wof_chunk_table() and ntfs_read_wof_chunk() already take the buffer
as a parameter and both set *chunk_mem to a pointer inside it, so a
caller-owned buffer works unchanged.
Allocate that buffer per call, do both reads without the lock, and take
the lock only around decompression, which is the step needing ws->output
and ws->scratch. squashfs is arranged this way already: its
squashfs_decompress() is handed a bio that has been read, and locks only
for the CPU work.
Block reads are unchanged in number, they just no longer run under the
lock, and hold time stops tracking device speed.
This also unnests two per-inode locks from the global one, runlist->lock
taken by both reads and base_ni->mrec_lock taken for a resident stream.
A resident chunk needs no I/O at all, yet used to queue behind a reader
blocked in submit_bio_wait() and then take mrec_lock inside the global
mutex.
The buffer is 4608 bytes for xpress4k and at most 33280 for lzx32k. This
path already does GFP_NOFS allocations per call in ntfs_attr_iget(), and
in ntfs_attr_get_search_ctx() for a resident stream, so one more does not
change how it behaves under memory pressure. The workspace keeps output
and scratch, 4 KiB to 32 KiB and 6224 bytes (xpress) or 10240 (lzx), and
its "already allocated" test moves from ws->input to ws->output.
The lock is now taken per chunk rather than per call, which differs only
for a folio spanning several chunks: a few more uncontended mutex
operations in exchange for not holding it across the reads between them.
Verified under QEMU against an uncompressed copy of the same data, on an
8 MiB file and a 100000 byte one, the latter covering the tail chunk that
is not a full comp_unit.
Signed-off-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
|
History
|
|
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .pylintrc | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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 * AI Coding Assistant: LLMs and AI-powered development tools 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 AI Coding Assistant ------------------- CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and follow the AI coding assistants documentation before contributing to the Linux kernel: * Documentation/process/coding-assistants.rst This documentation contains essential requirements about licensing, attribution, and the Developer Certificate of Origin that all AI tools must comply with. 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