linux-kernel - Re: [PATCH v7 0/6] block: loop: improve loop with AIO

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Date:	Thu, 23 Jul 2015 05:00:35 -0400
From:	Ming Lei <ming.lei@...onical.com>
To:	Jens Axboe <axboe@...nel.dk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	"Justin M. Forbes" <jforbes@...oraproject.org>,
	Jeff Moyer <jmoyer@...hat.com>, Tejun Heo <tj@...nel.org>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH v7 0/6] block: loop: improve loop with AIO

On Thu, Jul 16, 2015 at 11:37 AM, Ming Lei <ming.lei@...onical.com> wrote:
> Hi Guys,
>
> There are about 3 advantages to use direct I/O and AIO on
> read/write loop's backing file:
>
> 1) double cache can be avoided, then memory usage gets
> decreased a lot
>
> 2) not like user space direct I/O, there isn't cost of
> pinning pages
>
> 3) avoid context switch for obtaining good throughput
> - in buffered file read, random I/O throughput is often obtained
> only if they are submitted concurrently from lots of tasks; but for
> sequential I/O, most of times they can be hit from page cache, so
> concurrent submissions often introduce unnecessary context switch
> and can't improve throughput much. There was such discussion[1]
> to use non-blocking I/O to improve the problem for application.
> - with direct I/O and AIO, concurrent submissions can be
> avoided and random read throughput can't be affected meantime
>
> So this patchset trys to improve loop via AIO, and about 45% memory
> usage can be decreased, see detailed data in commit log of patch4,
> also IO throughput isn't affected too.
>
> V7:
>         - only 4/6 and 5/6 updated
>         - update direct io after lo->offset is changed(4/6)
>         - fix updating LO_FLAGS_DIRECT_IO in __loop_update_dio()(4/6)
>         - introduce ioctl cmd of LOOP_SET_DIRECT_IO(5/6) for case of
>           'mount -o loop'
>         - losetup git tree:
>             http://kernel.ubuntu.com/git/ming/util-linux.git/log/?h=loop-dio-v7
>         - how to set direct io
>             losetup --direct-io 1 /dev/loopN
>         - how to clear direct io
>             losetup --direct-io 0 /dev/loopN
>         - how to show if direct io is used for accessing backing file
>             losetup -l
> V6:
>         - only patch 4 and patch 5 get updated
>         - check lo->lo_offset to decide if direct IO can be supported(4/5)
>         - introduce one flag for userspace(losetup) to keep updated
>         if using direct I/O to access backing file(4/5)
>         - implement patches for util-linux(losetup) so that losetup can
>         enable direct I/O feature:(4/5)
>
>            http://kernel.ubuntu.com/git/ming/util-linux.git/log/?h=losetup-dio
>
>         - remove the direct IO control interface from sysfs(4/5)
>         - handle partial read in case of direct read (5/5)
>         - add more comments for direct IO (5/5)
> V5:
>         - don't introduce IOCB_DONT_DIRTY_PAGE and bypass dirtying
>         for ITER_KVEC and ITER_BVEC direct IO(read), as required by
>         Christoph
>
> V4:
>         - add detailed commit log for 'use kthread_work'
>         - allow userspace(sysfs, losetup) to decide if dio/aio is
>         used as suggested by Christoph and Dave Chinner
>         - only use dio if the backing block device's min io size
>         is 512 as pointed by Dave Chinner & Christoph
> V3:
>         - based on Al's iov_iter work and Christoph's kiocb changes
>         - use kthread_work
>         - introduce IOCB_DONT_DIRTY_PAGE flag
>         - set QUEUE_FLAG_NOMERGES for loop's request queue
> V2:
>         - remove 'extra' parameter to aio_kernel_alloc()
>         - try to avoid memory allcation inside queue req callback
>         - introduce 'use_mq' sysfs file for enabling kernel aio or disabling it
> V1:
>         - link:
>                 http://marc.info/?t=140803157700004&r=1&w=2
>         - improve failure path in aio_kernel_submit()
>
>  drivers/block/loop.c      | 263 ++++++++++++++++++++++++++++++++++++----------
>  drivers/block/loop.h      |  13 +--
>  fs/direct-io.c            |   9 +-
>  include/uapi/linux/loop.h |   2 +
>  4 files changed, 221 insertions(+), 66 deletions(-)

Hi Guys,

Gentle ping.

thanks,
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