linux-kernel - Re: [PATCH v5 05/12] block: Kill bi

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Message-ID: <20120815221936.GC2758@google.com>
Date:	Wed, 15 Aug 2012 15:19:36 -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, agk@...hat.com,
	neilb@...e.de, drbd-dev@...ts.linbit.com, vgoyal@...hat.com,
	mpatocka@...hat.com, sage@...dream.net, yehuda@...newdream.net
Subject: Re: [PATCH v5 05/12] block: Kill bi_destructor

On Wed, Aug 08, 2012 at 11:34:09PM -0700, Tejun Heo wrote:
> Hello,
> 
> On Wed, Aug 8, 2012 at 11:12 PM, Kent Overstreet <koverstreet@...gle.com> wrote:
> > But if it's a pointer to heap allocated memory, but the bio was embedded
> > in another struct? I've seen a fair number of instances of that (md, off
> > the top of my head).
> >
> > If you're sure that in a normal config the slab allocator is going to
> > complain right away and not corrupt itself, fine. But I've been bitten
> > way too hard by bugs that could've been caught right away by a simple
> > assert and instead I had to spend hours backtracking, and the block
> > layer is _rife_ with that kind of thing.
> 
> Let's let slab debug code deal with that.  I really don't see much
> benefit in doing this.  The said kind of bugs aren't particularly
> difficult to track down.

The only difference would be changing
#define BIO_KMALLOC_POOL ((void *) ~0)

to
#define BIO_KMALLOC_POOL NULL

We want a define for this - bio_alloc_bioset(GFP_KERNEL, 1, NULL)
doesn't make any sense. I just don't see the argument for changing an
arbitrary constant... If it's just the ~0 pointer you don't like, I
originally used a real statically allocated struct bio_set as a sentinel
value.
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