From: Ted Ts'o <tytso@mit.edu>
To: Zach Brown <zab@zabbo.net>
Cc: Dave Kleikamp <dave.kleikamp@oracle.com>,
linux-fsdevel@vger.kernel.org,
Chris Mason <chris.mason@oracle.com>
Subject: Re: Use case for "loop: Issue O_DIRECT aio with pages"?
Date: Fri, 2 Mar 2012 03:14:07 -0500 [thread overview]
Message-ID: <20120302081407.GA22215@thunk.org> (raw)
In-Reply-To: <4F503545.8030308@zabbo.net>
On Thu, Mar 01, 2012 at 09:49:41PM -0500, Zach Brown wrote:
>
> >*why* is it interesting to allow kernel code to submit aio
> >requests, and loop devices to be able to direct I/O requests all the
> >way to the underlying file systems.
>
> As I understood it, lo those years ago, the use case was virtual guests
> provisioned on loopback devices on files in the host file system.
>
> In this use case either having loop implement a second writeback cache
> or having it only capable of one sync IO in flight at a time is pretty
> bad when you're trying to offer consistent and performant file systems
> to the guest.
I'm confused though why the guests would be pointed at the loopback
device, as opposed to just simply attaching to the file directly. Or
is this some kind of Xen limitation? With qemu/kvm I don't see why it
would make sense to indirect through the loop device....
- Ted
next prev parent reply other threads:[~2012-03-02 8:14 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-01 23:15 Use case for "loop: Issue O_DIRECT aio with pages"? Ted Ts'o
2012-03-02 2:49 ` Zach Brown
2012-03-02 8:14 ` Ted Ts'o [this message]
2012-03-02 14:52 ` Zach Brown
2012-03-02 7:29 ` Christoph Hellwig
2012-03-02 14:14 ` Chris Mason
2012-03-02 20:50 ` James Bottomley
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