linux-kernel - Re: [PATCH V5 00/30] loop: Issue O_DIRECT aio using bio

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Message-ID: <1358353978.2384.50.camel@dabdike.int.hansenpartnership.com>
Date:	Wed, 16 Jan 2013 16:32:58 +0000
From:	James Bottomley <jbottomley@...allels.com>
To:	Dave Kleikamp <dave.kleikamp@...cle.com>
CC:	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Zach Brown <zab@...bo.net>,
	Maxim Patlasov <MPatlasov@...allels.com>
Subject: Re: [PATCH V5 00/30] loop: Issue O_DIRECT aio using bio_vec

On Wed, 2013-01-09 at 13:58 -0600, Dave Kleikamp wrote:
> This patchset was begun by Zach Brown and was originally submitted for
> review in October, 2009. Feedback was positive, and I have picked up
> where he left off, porting his patches to the latest mainline kernel
> and adding support more file systems.
> 
> 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.
> 
> This series was written to reduce the current overhead loop imposes by
> performing synchronus buffered file system IO from a kernel thread.  These
> patches turn loop into a light weight layer that translates bios into iocbs.
> 
> It introduces new file ops, read_iter() and write_iter(), that replace the
> aio_read() and aio_write() operations. The iov_iter structure can now contain
> either a user-space iovec or a kernel-space bio_vec. Since it would be
> overly complicated to replace every instance of aio_read() and aio_write(),
> the old operations are not removed, but file systems implementing the new
> ones need not keep the old ones.
> 
> Changes from V4 include:
>  * moved iov-iter.c from mm/ to fs/
>  * removed dio_aligned helper
>  * insured that FUA write to loop device is committed to media
>  * removed no-longer-used REQ_KERNEL define
> 
> These patches apply to 3.8-rc2 and are also available at:
> git://github.com/kleikamp/linux-shaggy.git loop_2013_01_04
> 
> My hopes are that this patchset is finally ready for linux-next.

Just a note that we at parallels are anxiously awaiting this too.  Our
rewrite of the linux loop device to be more efficient (and not double
cache) depends on this work.  I should also note that we've been testing
these patches (albeit backported to a RHEL kernel as a current work
base) with no problems reported so far.

James

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