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SubjectRe: [PATCH v4 0/4] block: loop: improve loop with AIO
From
Hi Guys,

On Fri, May 29, 2015 at 2:35 PM, Ming Lei <ming.lei@canonical.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.
>
> 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

Gentle ping, :-)

>
> 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()
>
>


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