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Analysis of recent reports of log reservation overruns and code inspection has uncovered that the reservations associated with inode operations may not cover the worst case scenarios. In particular, many cases only include one allocfree res. for a particular operation even though said operations may also entail AGFL fixups and inode btree block allocations in addition to the actual inode chunk allocation. This can easily turn into two or three block allocations (or frees) per operation. In theory, the only way to define the worst case reservation is to include an allocfree res for each individual allocation in a transaction. Since that is impractical (we can perform multiple agfl fixups per tx and not every allocation results in a full tree operation), we need to find a reasonable compromise that addresses the deficiency in practice without blowing out the size of the transactions. Since the inode btrees are not filled by the AGFL, record insertion and removal can directly result in block allocations and frees depending on the shape of the tree. These allocations and frees occur in the same transaction context as the inobt update itself, but are separate from the allocation/free that might be required for an inode chunk. Therefore, it makes sense to assume that an [f]inobt insert/remove can directly result in one or more block allocations on behalf of the tree. Refactor the inode transaction reservations to include one allocfree res. per inode btree modification to cover allocations required by the tree itself. This separates the reservation required to allocate the inode chunk from the reservation required for inobt record insertion/removal. Apply the same logic to the finobt. This results in killing off the finobt modify condition because we no longer assume that the broader transaction reservation will cover finobt block allocations and finobt shape changes can occur in either of the inobt allocation or modify situations. Suggested-by: Dave Chinner <david@fromorbit.com> Signed-off-by: Brian Foster <bfoster@redhat.com> Reviewed-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> |
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.