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A long time ago, I added to XFS the ability to use deferred reference count operations as part of a transaction chain. This enabled us to avoid blowing out the transaction reservation when the blocks in a physical extent all had different reference counts because we could ask the deferred operation manager for a continuation, which would get us a clean transaction. The refcount code asks for a continuation when the number of refcount record updates reaches the point where we think that the transaction has logged enough full btree blocks due to refcount (and free space) btree shape changes and refcount record updates that we're in danger of overflowing the transaction. We did not previously count the EFIs logged to the refcount update transaction because the clamps on the length of a bunmap operation were sufficient to avoid overflowing the transaction reservation even in the worst case situation where every other block of the unmapped extent is shared. Unfortunately, the restrictions on bunmap length avoid failure in the worst case by imposing a maximum unmap length of ~3000 blocks, even for non-pathological cases. This seriously limits performance when freeing large extents. Therefore, track EFIs with the same counter as refcount record updates, and use that information as input into when we should ask for a continuation. This enables the next patch to drop the clumsy bunmap limitation. Depends:27dada070d("xfs: change the order in which child and parent defer ops ar finished") Depends:74f4d6a1e0("xfs: only relog deferred intent items if free space in the log gets low") Signed-off-by: Darrick J. Wong <djwong@kernel.org> Reviewed-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de>
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.