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Date: Thu, 10 Jan 2002 11:47:04 +0100
From: Andrea Arcangeli <andrea@suse.de>
To: Jens Axboe <axboe@suse.de>
Cc: Badari Pulavarty <pbadari@us.ibm.com>, Benjamin LaHaise <bcrl@redhat.com>,
        linux-kernel@vger.kernel.org, marcelo@conectiva.com.br
Subject: Re: [PATCH] PAGE_SIZE IO for RAW (RAW VARY)
Message-ID: <20020110114704.I3357@inspiron.school.suse.de>
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On Thu, Jan 10, 2002 at 11:22:25AM +0100, Jens Axboe wrote:
> On Thu, Jan 10 2002, Andrea Arcangeli wrote:
> > On Wed, Jan 09, 2002 at 11:28:39AM -0800, Badari Pulavarty wrote:
> > > Ben,
> > > 
> > > By any chance do you have a list of drivers that assume this ? 
> > > What does it take to fix them ? 
> > > 
> > > I think Jens BIO changes for 2.5 will fix this problem. But 
> > > 2.4 needs a solution in this area too. This patch showed 
> > > significant improvement for database workloads. 
> > 
> > I didn't checked the implementation but as far as the blkdev is
> > concerned the b_size changes without notification as soon as you 'mkfs
> > -b somethingelse' and then mount the fs. So it cannot break as far I can
> > tell. The only important thing is that b_size stays between 512 and 4k.
> 
> The concern is/was differently sized buffer_heads in the same request,
> ie b_size changing as you iterate through the chunks of one request.

ok, I don't expect problems there. It can happen for example if you
create a snapshot with 4k and then you switch back the original volume
to 1k. the physical volume will get mixed b_size colaesced into the same
request.

Andrea
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