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When an XFS filesystem has free inodes in chunks already allocated on disk, it will still allocate new inode chunks if the target AG has no free inodes in it. Normally, this is a good idea as it preserves locality of all the inodes in a given directory. However, at ENOSPC this can lead to using the last few remaining free filesystem blocks to allocate a new chunk when there are many, many free inodes that could be allocated without consuming free space. This results in speeding up the consumption of the last few blocks and inode create operations then returning ENOSPC when there free inodes available because we don't have enough block left in the filesystem for directory creation reservations to proceed. Hence when we are near ENOSPC, we should be attempting to preserve the remaining blocks for directory block allocation rather than using them for unnecessary inode chunk creation. This particular behaviour is exposed by xfs/294, when it drives to ENOSPC on empty file creation whilst there are still thousands of free inodes available for allocation in other AGs in the filesystem. Hence, when we are within 1% of ENOSPC, change the inode allocation behaviour to prefer to use existing free inodes over allocating new inode chunks, even though it results is poorer locality of the data set. It is more important for the allocations to be space efficient near ENOSPC than to have optimal locality for performance, so lets modify the inode AG selection code to reflect that fact. This allows generic/294 to not only pass with this allocator rework patchset, but to increase the number of post-ENOSPC empty inode allocations to from ~600 to ~9080 before we hit ENOSPC on the directory create transaction reservation. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Allison Henderson <allison.henderson@oracle.com> Reviewed-by: Darrick J. Wong <djwong@kernel.org> |
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| 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.