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

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Date:	Thu, 17 Jan 2013 23:49:37 +0000
From:	James Bottomley <jbottomley@...allels.com>
To:	"sedat.dilek@...il.com" <sedat.dilek@...il.com>
CC:	Dave Kleikamp <dave.kleikamp@...cle.com>,
	"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, 2013-01-16 at 19:25 +0100, Sedat Dilek wrote:
> On Wed, Jan 16, 2013 at 5:32 PM, James Bottomley
> <jbottomley@...allels.com> wrote:
> > 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.
> >
> 
> Hi James,
> 
> do you have a location for me for testing this patchset from parallels?

You mean the RHEL kernels?  Not really; they're just proof of concept
and not released yet.  Our mainline effort won't really begin until we
know the fate of the DIO patches.

James

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