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From: Goldwyn Rodrigues <>
Subject: [PATCH 0/8 v6] No wait AIO
Date: Fri, 14 Apr 2017 07:02:49 -0500	[thread overview]
Message-ID: <> (raw)

Formerly known as non-blocking AIO.

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, BIO_NOWAIT for bio 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.
Same with QUEUE_FLAG_NOWAIT, which is currently set for sd and virtio devices.
This is primarily to block md/dm devices which may wait in places such as
recovery/sync/suspend. In the future, I intend to add support to
these devices as well. Applications will have to check supportability
by sending a async direct write and any other error besides -EAGAIN
would mean it is not supported.

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

 Changes since v5:
  + Common helper for RWF flags.


             reply	other threads:[~2017-04-14 12:02 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-04-14 12:02 Goldwyn Rodrigues [this message]
     [not found] ` <>
2017-04-14 12:02   ` [PATCH 1/8] Use RWF_* flags for AIO operations Goldwyn Rodrigues
     [not found]     ` <>
2017-04-19  6:37       ` Christoph Hellwig
2017-04-14 12:02 ` [PATCH 2/8] nowait aio: Introduce RWF_NOWAIT Goldwyn Rodrigues
2017-04-19  6:39   ` Christoph Hellwig
     [not found]     ` <>
2017-04-19 10:30       ` Goldwyn Rodrigues
     [not found]         ` <>
2017-04-19 11:03           ` Jan Kara
2017-04-14 12:02 ` [PATCH 3/8] nowait aio: return if direct write will trigger writeback Goldwyn Rodrigues
2017-04-14 12:02 ` [PATCH 4/8] nowait-aio: Introduce IOMAP_NOWAIT Goldwyn Rodrigues
2017-04-19  6:39   ` Christoph Hellwig
     [not found]   ` <>
2017-04-19  7:12     ` Jan Kara
2017-04-14 12:02 ` [PATCH 5/8] nowait aio: return on congested block device Goldwyn Rodrigues
2017-04-19  6:45   ` Christoph Hellwig
2017-04-19 15:21     ` Goldwyn Rodrigues
2017-04-20 13:43       ` Jan Kara
2017-04-24 21:10     ` Goldwyn Rodrigues
2017-04-25  2:28       ` Jens Axboe
2017-04-14 12:02 ` [PATCH 6/8] nowait aio: ext4 Goldwyn Rodrigues
2017-04-14 12:02 ` [PATCH 7/8] nowait aio: xfs Goldwyn Rodrigues
2017-04-19  6:45   ` Christoph Hellwig
2017-04-14 12:02 ` [PATCH 8/8] nowait aio: btrfs Goldwyn Rodrigues
     [not found]   ` <>
2017-04-18 11:39     ` David Sterba

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