linux-kernel - Re: [PATCH v2 19/26] bounce: Refactor __blk_queue_bounce to not use bi_io

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Message-ID: <20120921002555.GV7264@google.com>
Date:	Thu, 20 Sep 2012 17:25:55 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Kent Overstreet <koverstreet@...gle.com>
Cc:	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, axboe@...nel.dk, neilb@...e.de
Subject: Re: [PATCH v2 19/26] bounce: Refactor __blk_queue_bounce to not
 use bi_io_vec

Hello, Kent.

On Mon, Sep 10, 2012 at 05:22:30PM -0700, Kent Overstreet wrote:
> A bunch of what __blk_queue_bounce() was doing was problematic for the
> immutable bvec work; this cleans that up and the code is quite a bit
> smaller, too.
> 
> The __bio_for_each_segment() in copy_to_high_bio_irq() was changed
> because that one's looping over the original bio, not the bounce bio -
> since the bounce code doesn't own that bio the __ version wasn't
> correct.

I do like the new implementation.  I think the function is broken
before and after tho.  Allocating from fs_bio_set from block layer is
never safe and nothing seems to prevent multiple allocators compete in
the bounce page mempool.  This will need a separate bioset and the
multiple mempool allocation would have to be put inside a mutex.

Also, how was this tested?

Thanks.

-- 
tejun
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