From: Tejun Heo <tj@kernel.org>
To: Kent Overstreet <koverstreet@google.com>
Cc: linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org,
dm-devel@redhat.com, vgoyal@redhat.com, mpatocka@redhat.com,
bharrosh@panasas.com, Jens Axboe <axboe@kernel.dk>
Subject: Re: [PATCH v6 06/13] block: Consolidate bio_alloc_bioset(), bio_kmalloc()
Date: Fri, 24 Aug 2012 13:08:35 -0700 [thread overview]
Message-ID: <20120824200835.GD21325@google.com> (raw)
In-Reply-To: <20120824050400.GA11977@moria.home.lan>
Hello,
On Thu, Aug 23, 2012 at 10:04:00PM -0700, Kent Overstreet wrote:
> > > struct bio *bio_alloc_bioset(gfp_t gfp_mask, int nr_iovecs, struct bio_set *bs)
> > > {
> > > + unsigned front_pad;
> > > + unsigned inline_vecs;
> > > unsigned long idx = BIO_POOL_NONE;
> > > struct bio_vec *bvl = NULL;
> > > struct bio *bio;
> > > void *p;
> > >
> > > - p = mempool_alloc(bs->bio_pool, gfp_mask);
> > > + if (nr_iovecs > UIO_MAXIOV)
> > > + return NULL;
> >
> > This test used to only happen for bio_kmalloc(). If I follow the code
> > I can see that UIO_MAXIOV is larger than BIOVEC_MAX_IDX, so this
> > doesn't really affect the capability of bioset allocs; however, given
> > that bioset allocation already checks against BIOVEC_MAX_IDX, I don't
> > see why this test is now also applied to them.
>
> Having arbitrary limits that are different for kmalloced bios and bioset
> allocated bios seems _very_ sketchy to me. I tend to think that
> UIO_MAXIOV check shouldn't be there at all... but if it is IMO it makes
> slightly more sense for it to apply to all bio allocations.
>
> As you mentioned it doesn't affect the behaviour of the code, but
> supposing UIO_MAXIOV was less than BIO_MAX_PAGES, whatever was depending
> on that check would then implicitly depend on the bios not being
> allocated from a bioset. Ugly.
Please keep UIO_MAXIOV test on kmalloc case only. If you want to
change that, please do that in a separate patch with its own
justification.
> > And we lose /** comments on two exported functions and
> > bio_alloc_bioset() comment doesn't explain that it now also handles
> > NULL bioset case. Now that they share common implementation, you can
> > update bio_alloc_bioset() and refer to it from its wrappers but please
> > don't drop them like this.
>
> So if I follow you, you're fine with dropping the comments from the
> single line wrappers provided their information is rolled into
> bio_alloc_bioset()'s documentation? That's what I should have done,
> I'll do that now.
Not really, for example, if you had
/* explain A in detail */
a() {};
and if you introduce __a() which does __A and make a its wrapper.
/* explain __A in detail */
__a() {};
/* explain A briefly and refer to __a() for details */
a() {};
Thanks.
--
tejun
next prev parent reply other threads:[~2012-08-24 20:08 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-22 17:03 [PATCH v6 00/13] Block cleanups Kent Overstreet
2012-08-22 17:03 ` [PATCH v6 01/13] block: Generalized bio pool freeing Kent Overstreet
2012-08-22 21:27 ` Nicholas A. Bellinger
2012-08-22 17:03 ` [PATCH v6 02/13] dm: Use bioset's front_pad for dm_rq_clone_bio_info Kent Overstreet
2012-08-22 18:32 ` Tejun Heo
2012-08-22 21:30 ` Vivek Goyal
2012-08-24 7:14 ` Kent Overstreet
2012-08-24 18:40 ` Vivek Goyal
2012-08-22 17:04 ` [PATCH v6 03/13] block: Add bio_reset() Kent Overstreet
2012-08-22 18:34 ` Tejun Heo
2012-08-22 19:51 ` Tejun Heo
2012-08-22 17:04 ` [PATCH v6 04/13] pktcdvd: Switch to bio_kmalloc() Kent Overstreet
2012-08-22 19:55 ` Tejun Heo
2012-08-28 23:19 ` Jiri Kosina
2012-08-29 4:35 ` Peter Osterlund
2012-09-03 16:15 ` Jiri Kosina
2012-08-22 17:04 ` [PATCH v6 05/13] block: Kill bi_destructor Kent Overstreet
2012-08-22 20:00 ` Tejun Heo
2012-08-24 5:09 ` Kent Overstreet
2012-08-22 17:04 ` [PATCH v6 06/13] block: Consolidate bio_alloc_bioset(), bio_kmalloc() Kent Overstreet
2012-08-22 20:17 ` Tejun Heo
2012-08-24 5:04 ` Kent Overstreet
2012-08-24 20:08 ` Tejun Heo [this message]
2012-08-22 17:04 ` [PATCH v6 07/13] block: Avoid deadlocks with bio allocation by stacking drivers Kent Overstreet
2012-08-22 20:30 ` Tejun Heo
2012-08-24 5:55 ` Kent Overstreet
2012-08-24 20:28 ` Tejun Heo
2012-08-22 17:04 ` [PATCH v6 08/13] block: Add an explicit bio flag for bios that own their bvec Kent Overstreet
2012-08-22 17:43 ` Adrian Bunk
2012-08-22 19:22 ` Kent Overstreet
2012-08-22 20:00 ` Adrian Bunk
2012-08-28 17:23 ` Kent Overstreet
2012-08-22 17:04 ` [PATCH v6 09/13] block: Rename bio_split() -> bio_pair_split() Kent Overstreet
2012-08-22 17:04 ` [PATCH v6 10/13] block: Introduce new bio_split() Kent Overstreet
2012-08-22 20:46 ` Tejun Heo
2012-08-22 17:04 ` [PATCH v6 11/13] block: Rework bio_pair_split() Kent Overstreet
2012-08-22 21:04 ` Tejun Heo
2012-08-24 2:25 ` Martin K. Petersen
2012-08-24 10:37 ` Kent Overstreet
2012-08-24 20:58 ` Tejun Heo
2012-08-24 10:30 ` Kent Overstreet
2012-08-24 20:53 ` Tejun Heo
2012-08-22 17:04 ` [PATCH v6 12/13] block: Add bio_clone_bioset(), bio_clone_kmalloc() Kent Overstreet
2012-08-22 17:13 ` Jeff Garzik
2012-08-22 21:07 ` Tejun Heo
2012-08-24 6:24 ` Kent Overstreet
2012-08-24 20:36 ` Tejun Heo
2012-08-22 17:04 ` [PATCH v6 13/13] block: Only clone bio vecs that are in use Kent Overstreet
2012-08-22 21:10 ` Tejun Heo
2012-08-24 7:05 ` Kent Overstreet
2012-08-24 20:42 ` Tejun Heo
2012-08-23 18:00 ` [PATCH v6 00/13] Block cleanups Vivek Goyal
2012-08-24 12:46 ` Kent Overstreet
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