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When the swap device is full (inuse_pages == pages), it should be removed from the allocation available plist. If any slot is freed, the swap device should be added back to the plist. Additionally, during swapon or swapoff, the swap device is forcefully added or removed. Currently, the condition (inuse_pages == pages) is checked after every counter update, then remove or add the device accordingly. This is serialized by si->lock. This commit decouples it from the protection of si->lock and reworked plist removal and adding, making it possible to get rid of the hard dependency on si->lock in allocation path in later commits. To achieve this, simply using another lock is not an optimal approach, as the overhead is observable for a hot counter, and may cause complex locking issues. Thus, this commit manages to make it a lock-free atomic operation, by embedding the plist state into the second highest bit of the atomic counter. Simply making the counter an atomic will not work, if the update and plist status check are not performed atomically, we may miss an addition or removal. With the embedded info we can update the counter and check the plist status with single atomic operations, and avoid any extra overheads: If the counter is full (inuse_pages == pages) and the off-list bit is unset, we attempt to remove it from the plist. If the counter is not full (inuse_pages != pages) and the off-list bit is set, we attempt to add it to the plist. Removing, adding and bit update is serialized with a lock, which is a cold path. Ordinary counter updates will be lock-free. Link: https://lkml.kernel.org/r/20250113175732.48099-7-ryncsn@gmail.com Signed-off-by: Kairui Song <kasong@tencent.com> Cc: Baoquan He <bhe@redhat.com> Cc: Barry Song <v-songbaohua@oppo.com> Cc: Chis Li <chrisl@kernel.org> Cc: "Huang, Ying" <ying.huang@linux.alibaba.com> Cc: Hugh Dickens <hughd@google.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Kalesh Singh <kaleshsingh@google.com> Cc: Nhat Pham <nphamcs@gmail.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Yosry Ahmed <yosryahmed@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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| 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 | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.