From: Goldwyn Rodrigues Subject: [PATCH 0/10 v11] No wait AIO Date: Tue, 6 Jun 2017 06:19:29 -0500 Message-ID: <20170606111939.27272-1-rgoldwyn@suse.de> Cc: jack@suse.com, hch@infradead.org, linux-block@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, axboe@kernel.dk, linux-api@vger.kernel.org, adam.manzanares@wdc.com, viro@zeniv.linux.org.uk To: linux-fsdevel@vger.kernel.org Return-path: Sender: linux-block-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org 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