linux-kernel - Re: [PATCH 3/6] direct-io: do not merge logically non-contiguous requests

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Message-ID: <20100522140217.GS32248@dhcp231-156.rdu.redhat.com>
Date:	Sat, 22 May 2010 10:02:17 -0400
From:	Josef Bacik <josef@...hat.com>
To:	Mike Fedyk <mfedyk@...efedyk.com>
Cc:	Josef Bacik <josef@...hat.com>, linux-btrfs@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	hch@...radead.org, akpm@...ux-foundation.org
Subject: Re: [PATCH 3/6] direct-io: do not merge logically non-contiguous
	requests

On Fri, May 21, 2010 at 06:47:36PM -0700, Mike Fedyk wrote:
> On Fri, May 21, 2010 at 10:03 AM, Josef Bacik <josef@...hat.com> 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.
> >
> > Signed-off-by: Josef Bacik <josef@...hat.com>
> > ---
> >
> > V1->V2
> > -Be more verbose in the in-code comment
> >
> >  fs/direct-io.c |   20 ++++++++++++++++++--
> >  1 files changed, 18 insertions(+), 2 deletions(-)
> >
> 
> Btrfs has been pretty much self-contained (working well compiled
> against 2.6.32 for example).  Is there a way that this wouldn't just
> start silently breaking for people compiling the latest btrfs with
> dkms against older kernels?

Nope, you have to have these generic patches for DIO to work, so building btrfs
like this will stop working with earlier kernels.  Thanks,

Josef
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