As already indicated this whole series looks fine to me.
Al: are you going to pick this up? Or Andrew?
On Tue, Jun 06, 2017 at 06:19:29AM -0500, Goldwyn Rodrigues wrote:
> This series adds nonblocking feature to asynchronous I/O writes.
> io_submit() can be delayed because of a number of reason:
> - Block allocation for files
> - Data writebacks for direct I/O
> - Sleeping because of waiting to acquire i_rwsem
> - Congested block device
>
> The goal of the patch series is to return -EAGAIN/-EWOULDBLOCK if
> any of these conditions are met. This way userspace can push most
> of the write()s to the kernel to the best of its ability to complete
> and if it returns -EAGAIN, can defer it to another thread.
>
> In order to enable this, IOCB_RW_FLAG_NOWAIT is introduced in
> uapi/linux/aio_abi.h. If set for aio_rw_flags, it translates to
> IOCB_NOWAIT for struct iocb, REQ_NOWAIT for bio.bi_opf and IOMAP_NOWAIT for
> iomap. aio_rw_flags is a new flag replacing aio_reserved1. We could
> not use aio_flags because it is not currently checked for invalidity
> in the kernel.
>
> This feature is provided for direct I/O of asynchronous I/O only. I have
> tested it against xfs, ext4, and btrfs while I intend to add more filesystems.
> The nowait feature is for request based devices. In the future, I intend to
> add support to stacked devices such as md.
>
> Applications will have to check supportability
> by sending a async direct write and any other error besides -EAGAIN
> would mean it is not supported.
>
> First two patches are prep patches into nowait I/O.
>
> Changes since v1:
> + changed name from _NONBLOCKING to *_NOWAIT
> + filemap_range_has_page call moved to closer to (just before) calling
> filemap_write_and_wait_range().
> + BIO_NOWAIT limited to get_request()
> + XFS fixes
> - included reflink
> - use of xfs_ilock_nowait() instead of a XFS_IOLOCK_NONBLOCKING flag
> - Translate the flag through IOMAP_NOWAIT (iomap) to check for
> block allocation for the file.
> + ext4 coding style
>
> Changes since v2:
> + Using aio_reserved1 as aio_rw_flags instead of aio_flags
> + blk-mq support
> + xfs uptodate with kernel and reflink changes
>
> Changes since v3:
> + Added FS_NOWAIT, which is set if the filesystem supports NOWAIT feature.
> + Checks in generic_make_request() to make sure BIO_NOWAIT comes in
> for async direct writes only.
> + Added QUEUE_FLAG_NOWAIT, which is set if the device supports BIO_NOWAIT.
> This is added (rather not set) to block devices such as dm/md currently.
>
> Changes since v4:
> + Ported AIO code to use RWF_* flags. Check for RWF_* flags in
> generic_file_write_iter().
> + Changed IOCB_RW_FLAGS_NOWAIT to RWF_NOWAIT.
>
> Changes since v5:
> + BIO_NOWAIT to REQ_NOWAIT
> + Common helper for RWF flags.
>
> Changes since v6:
> + REQ_NOWAIT will be ignored for request based devices since they
> cannot block. So, removed QUEUE_FLAG_NOWAIT since it is not
> required in the current implementation. It will be resurrected
> when we program for stacked devices.
> + changed kiocb_rw_flags() to kiocb_set_rw_flags() in order to accomodate
> for errors. Moved checks in the function.
>
> Changes since v7:
> + split patches into prep so the main patches are smaller and easier
> to understand
> + All patches are reviewed or acked!
>
> Changes since v8:
> + Err out AIO reads with -EINVAL flagged as RWF_NOWAIT
>
> Changes since v9:
> + Retract - Err out AIO reads with -EINVAL flagged as RWF_NOWAIT
> + XFS returns EAGAIN if extent list is not in memory
> + Man page updates to io_submit with iocb description and nowait features.
>
> Changes since v10:
> + Corrected comment and subject in "return on congested block device"
>
> --
> Goldwyn
>
>
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