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

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Date:	Thu, 20 Sep 2012 17:29:16 -0700
From:	Kent Overstreet <koverstreet@...gle.com>
To:	Tejun Heo <tj@...nel.org>
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

On Thu, Sep 20, 2012 at 05:25:55PM -0700, Tejun Heo wrote:
> 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.

Yeah, I should've at least made a note of that.

I should really add "audit all uses of fs_bio_set" to my todo list.

> Also, how was this tested?

Changed queue_bounce_pfn() to return 0, forcing all io to be bounced.
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