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Date: Tue, 11 Sep 2012 00:45:34 +0100
From: Alasdair G Kergon <agk@redhat.com>
To: Tejun Heo <tj@kernel.org>
Cc: Kent Overstreet <koverstreet@google.com>, axboe@kernel.dk,
        device-mapper development <dm-devel@redhat.com>, david@fromorbit.com,
        linux-kernel@vger.kernel.org, linux-bcache@vger.kernel.org,
        Mikulas Patocka <mpatocka@redhat.com>, bharrosh@panasas.com,
        Vivek Goyal <vgoyal@redhat.com>
Subject: Re: [dm-devel] [PATCH 2/2] block: Avoid deadlocks with bio
	allocation by stacking drivers
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On Mon, Sep 10, 2012 at 04:35:02PM -0700, Tejun Heo wrote:
> debug.  Would it be difficult to convert dm drivers to collect size
> requirements and use front-pad for all per-bio data?
 
I can't give a quick answer because a single bio may require a variable
number (depending on the bio content) of (sequential) mempool_allocs from the
same mempool to complete its processing, so we do have to audit all this very
carefully to see what can/can't be pulled out.

Alasdair