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Because the NFS client will already happily handle misaligned O_DIRECT IO (by sending it out to NFSD via RPC) this commit's new capabilities are for the benefit of LOCALIO. LOCALIO will make best effort to transform misaligned IO to DIO-aligned extents when possible. LOCALIO's READ and WRITE DIO that is misaligned will be split into as many as 3 component IOs (@start, @middle and @end) as needed -- IFF the @middle extent is verified to be DIO-aligned, and then the @start and/or @end are misaligned (due to each being a partial page). Otherwise if the @middle isn't DIO-aligned the code will fallback to issuing only a single contiguous buffered IO. The @middle is only DIO-aligned if both the memory and on-disk offsets for the IO are aligned relative to the underlying local filesystem's block device limits (@dma_alignment and @logical_block_size respectively). The misaligned @start and/or @end extents are issued using buffered IO and the DIO-aligned @middle is issued using O_DIRECT. The @start and @end IOs are issued first using buffered IO with IOCB_SYNC and then the @middle is issued last using direct IO with async completion (AIO). This out of order IO completion means that LOCALIO's IO completion code (nfs_local_read_done and nfs_local_write_done) is only called for the IO's last associated iov_iter completion. And in the case of DIO-aligned @middle it completes last using AIO. nfs_local_pgio_done() is updated to handle piece-wise partial completion of each iov_iter. This implementation for LOCALIO's misaligned DIO handling uses 3 iov_iter that share the same backing pages in their bio_vecs (so unfortunately 'struct nfs_local_kiocb' has 3 instead of only 1). [Reducing LOCALIO's per-IO (struct nfs_local_kiocb) memory use can be explored in the future. One logical progression to improve this code, and eliminate explicit loops over up to 3 iov_iter, is by extending 'struct iov_iter' to support iov_iter_clone() and iov_iter_chain() interfaces that are comparable to what 'struct bio' is able to support in the block layer. But even that wouldn't avoid the need to allocate/use up to 3 iov_iter] Signed-off-by: Mike Snitzer <snitzer@kernel.org> Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com> |
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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 | ||
| .pylintrc | ||
| .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.