linux-kernel - Re: [dm-devel] Re: [RFC PATCH 1/8] rqbased-dm: allow blk_get_request() to be called from interrupt context

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Message-ID: <20061221184051.GC17199@kernel.dk>
Date:	Thu, 21 Dec 2006 19:40:51 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Mike Christie <michaelc@...wisc.edu>
Cc:	device-mapper development <dm-devel@...hat.com>,
	mchristi@...hat.com, linux-kernel@...r.kernel.org, agk@...hat.com
Subject: Re: [dm-devel] Re: [RFC PATCH 1/8] rqbased-dm: allow blk_get_request()   to be called from interrupt context

On Thu, Dec 21 2006, Mike Christie wrote:
> Jens Axboe wrote:
> > On Thu, Dec 21 2006, Mike Christie wrote:
> >> Or the block layer code could set up the clone too. elv_next_request
> >> could prep a clone based on the orignal request for the driver then dm
> >> would not have to worry about that part.
> > 
> > It really can't, since it doesn't know how to allocate the clone
> > request. I'd rather export this functionality as helpers.
> > 
> 
> What do you think about dm's plan to break up make_request into a
> mapping function and in to the part the builds the bio into a request.
> This would fit well with them being helpers and being able to allocate
> the request from the correct context.

I think it sounds promising! dm probably still needs its own mempool for
request allocation, but that should be doable.

> I see patches for that did not get posted, but I thought Joe and
> Alasdair used to talk about that a lot and in the dm code I think there
> is sill comments about doing it. Maybe the dm comments mentioned the
> merge_fn, but I guess the merge_fn did not fit what they wanted to do or
> something. I think Alasdair talked about this at one of his talks at OLS
> or it was in a proposal for the kernel summit. I can dig up the mail if
> you want.

Not sure I remember the details of that one, so the mail/thread might be
useful.

-- 
Jens Axboe

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