Messages in this thread |  | | Date | Wed, 22 Nov 2017 13:49:31 -0500 | From | Mike Snitzer <> | Subject | Re: new patchset to eliminate DM's use of BIOSET_NEED_RESCUER |
| |
On Wed, Nov 22 2017 at 1:24pm -0500, Mikulas Patocka <mpatocka@redhat.com> wrote:
> Another problem is this: > > struct bio *b = bio_clone_bioset(bio, GFP_NOIO, md->queue->bio_split); > bio_advance(b, (bio_sectors(b) - ci.sector_count) << 9); > bio_chain(b, bio); > > What if it blocks because the bioset is exhausted? > > The code basically builds a chain of bios of unlimited length (suppose for > example a case when we are splitting on every sector boundary, so there > will be one bio for every sector in the original bio), it could exhaust > the bioset easily. > > It would be better to use mechanism from md-raid that chains all the > sub-bios to the same master bio and doesn't create long chains of bios: > > if (max_sectors < bio_sectors(bio)) { > struct bio *split = bio_split(bio, max_sectors, > gfp, conf->bio_split); > bio_chain(split, bio); > generic_make_request(bio); > bio = split; > r1_bio->master_bio = bio; > r1_bio->sectors = max_sectors; > }
I'd be happy to take an incremental patch that improves on this commit: https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-4.16&id=b46d6a08f1ae7bf53e4cde28e0ccdf91567d432e
But short of that I'll have to come back to this.
Thanks, Mike
|  |