From: Josef Bacik <josef@redhat.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Josef Bacik <josef@redhat.com>,
linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, akpm@linux-foundation.org
Subject: Re: [PATCH 3/6] direct-io: do not merge logically non-contiguous requests
Date: Fri, 21 May 2010 11:37:45 -0400 [thread overview]
Message-ID: <20100521153745.GP32248@dhcp231-156.rdu.redhat.com> (raw)
In-Reply-To: <20100521152111.GB16049@infradead.org>
On Fri, May 21, 2010 at 11:21:11AM -0400, Christoph Hellwig wrote:
> On Wed, May 19, 2010 at 04:24:51PM -0400, Josef Bacik wrote:
> > Btrfs cannot handle having logically non-contiguous requests submitted. For
> > example if you have
> >
> > Logical: [0-4095][HOLE][8192-12287]
> > Physical: [0-4095] [4096-8191]
> >
> > Normally the DIO code would put these into the same BIO's. The problem is we
> > need to know exactly what offset is associated with what BIO so we can do our
> > checksumming and unlocking properly, so putting them in the same BIO doesn't
> > work. So add another check where we submit the current BIO if the physical
> > blocks are not contigous OR the logical blocks are not contiguous.
>
> This gets us slightly less optimal I/O patters for other filesystems in
> this case. But it's probably corner case enough to not care and make it
> the default.
>
> But please make the comment in the comment as verbose as the commit
> message so that people understand why we're doing this when reading the
> code in a few years.
>
So after I sent this I thought that maybe I could make that test _only_ if we
provide submit_bio, that way it only affects btrfs and not everybody else, would
you prefer I do something like that? I will make the commit log a bit more
verbose. Thanks,
Josef
next prev parent reply other threads:[~2010-05-21 15:37 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-05-19 20:24 [PATCH 1/6] fs: allow short direct-io reads to be completed via buffered IO V2 Josef Bacik
2010-05-19 20:24 ` [PATCH 2/6] direct-io: add a hook for the fs to provide its own submit_bio function V3 Josef Bacik
2010-05-21 15:20 ` Christoph Hellwig
2010-05-19 20:24 ` [PATCH 3/6] direct-io: do not merge logically non-contiguous requests Josef Bacik
2010-05-21 15:21 ` Christoph Hellwig
2010-05-21 15:37 ` Josef Bacik [this message]
2010-05-21 15:35 ` Christoph Hellwig
2010-05-19 20:24 ` [PATCH 4/6] fs: kill blockdev_direct_IO_no_locking Josef Bacik
2010-05-21 15:21 ` Christoph Hellwig
2010-05-19 20:24 ` [PATCH 5/6] Btrfs: add basic DIO read/write support V6 Josef Bacik
2010-05-19 20:24 ` [PATCH 6/6] Btrfs: do aio_write instead of write V2 Josef Bacik
2010-05-21 17:03 [PATCH 1/6] fs: allow short direct-io reads to be completed via buffered IO Josef Bacik
2010-05-21 17:03 ` [PATCH 3/6] direct-io: do not merge logically non-contiguous requests Josef Bacik
2010-05-22 1:47 ` Mike Fedyk
2010-05-22 14:02 ` Josef Bacik
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