linux-kernel - Re: [PATCH v4 0/4] block: loop: improve loop with AIO

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Date:	Fri, 5 Jun 2015 16:26:16 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Dave Kleikamp <dave.kleikamp@...cle.com>
Cc:	Jens Axboe <axboe@...nel.dk>, Zach Brown <zab@...bo.net>,
	Christoph Hellwig <hch@...radead.org>,
	Maxim Patlasov <mpatlasov@...allels.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Tejun Heo <tj@...nel.org>, Dave Chinner <david@...morbit.com>
Subject: Re: [PATCH v4 0/4] block: loop: improve loop with AIO

Hi Guys,

On Fri, May 29, 2015 at 2:35 PM, 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.
>
> 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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