linux-kernel - Re: [dm-devel] [PATCH 2/2] block: Avoid deadlocks with bio allocation by stacking drivers

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Message-ID: <20120910234534.GD10477@agk-dp.fab.redhat.com>
Date:	Tue, 11 Sep 2012 00:45:34 +0100
From:	Alasdair G Kergon <agk@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Kent Overstreet <koverstreet@...gle.com>, axboe@...nel.dk,
	device-mapper development <dm-devel@...hat.com>,
	david@...morbit.com, linux-kernel@...r.kernel.org,
	linux-bcache@...r.kernel.org,
	Mikulas Patocka <mpatocka@...hat.com>, bharrosh@...asas.com,
	Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [dm-devel] [PATCH 2/2] block: Avoid deadlocks with bio
	allocation by stacking drivers

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

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