linux-kernel - Re: [PATCH V8 00/33] loop: Issue O_DIRECT aio using bio

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Date:	Wed, 21 Aug 2013 11:30:22 -0500
From:	Dave Kleikamp <dave.kleikamp@...cle.com>
To:	Benjamin LaHaise <bcrl@...ck.org>
CC:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Maxim V. Patlasov" <mpatlasov@...allels.com>,
	Zach Brown <zab@...bo.net>, linux-aio@...ck.org
Subject: Re: [PATCH V8 00/33] loop: Issue O_DIRECT aio using bio_vec

Ben,
First, let me apologize for neglecting to copy you and linux-aio on the
applicable patches. I've been carrying along this patchset, assuming I
had gotten the proper cc's correct a while back, but I somehow missed
the aio pieces.

On 08/21/2013 08:02 AM, Benjamin LaHaise wrote:
> Hello Dave,
> 
> On Thu, Jul 25, 2013 at 12:50:26PM -0500, Dave Kleikamp wrote:
>> This patch series adds a kernel interface to fs/aio.c so that kernel code can
>> issue concurrent asynchronous IO to file systems.  It adds an aio command and
>> file system methods which specify io memory with pages instead of userspace
>> addresses.
> 
> First off, have you tested that this series actually works when merged with 
> the pending AIO changes from Kent?  There a git tree with those pending 
> changes at git://git.kvack.org/~bcrl/aio-next.git , and they're in 
> linux-next.

I've lightly tested the patchset against the linux-next tree, running a
fio job on loop-mounted filesystems of different fs types.

> One of the major problems your changeset continues to carry is that your 
> new read_iter/write_iter operations permit blocking (implicitely), which 
> really isn't what we want for aio.  If you're going to introduce a new api, 
> it should be made non-blocking, and enforce that non-blocking requirement 
> (ie warn when read_iter/write_iter methods perform blockin operations, 
> similar to the warnings when scheduling in atomic mode).  This means more 
> changes for some filesystem code involved, something that people have been 
> avoiding for years, but which really needs to be done.

I'm not really sure how the read_iter and write_iter operations are more
likely to block than the current aio_read and aio_write operations. Am I
missing something?

Thanks,
Dave
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