9eb775968b
Callers of xfs_alloc_vextent_iterate_ags that pass in the TRYLOCK flag want us to perform a non-blocking scan of the AGs for free space. There are no ordering constraints for non-blocking AGF lock acquisition, so the scan can freely start over at AG 0 even when minimum_agno > 0. This manifests fairly reliably on xfs/294 on 6.3-rc2 with the parent pointer patchset applied and the realtime volume enabled. I observed the following sequence as part of an xfs_dir_createname call: 0. Fragment the free space, then allocate nearly all the free space in all AGs except AG 0. 1. Create a directory in AG 2 and let it grow for a while. 2. Try to allocate 2 blocks to expand the dirent part of a directory. The space will be allocated out of AG 0, but the allocation will not be contiguous. This (I think) activates the LOWMODE allocator. 3. The bmapi call decides to convert from extents to bmbt format and tries to allocate 1 block. This allocation request calls xfs_alloc_vextent_start_ag with the inode number, which starts the scan at AG 2. We ignore AG 0 (with all its free space) and instead scrape AG 2 and 3 for more space. We find one block, but this now kicks t_highest_agno to 3. 4. The createname call decides it needs to split the dabtree. It tries to allocate even more space with xfs_alloc_vextent_start_ag, but now we're constrained to AG 3, and we don't find the space. The createname returns ENOSPC and the filesystem shuts down. This change fixes the problem by making the trylock scan wrap around to AG 0 if it doesn't like the AGs that it finds. Since the current transaction itself holds AGF 0, the trylock of AGF 0 will succeed, and we take space from the AG that has plenty. Signed-off-by: Darrick J. Wong <djwong@kernel.org> Reviewed-by: Dave Chinner <dchinner@redhat.com> |
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| Documentation | ||
| LICENSES | ||
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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 Restructured Text 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.