From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760060Ab2IKTur (ORCPT ); Tue, 11 Sep 2012 15:50:47 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:42748 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760006Ab2IKTud (ORCPT ); Tue, 11 Sep 2012 15:50:33 -0400 Date: Tue, 11 Sep 2012 12:50:29 -0700 From: Kent Overstreet To: Mikulas Patocka Cc: "Alasdair G. Kergon" , Vivek Goyal , linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org, dm-devel@redhat.com, tj@kernel.org, bharrosh@panasas.com, Jens Axboe Subject: Re: [PATCH 2] dm: Use bioset's front_pad for dm_target_io Message-ID: <20120911195029.GJ19739@google.com> References: <20120829165006.GB20312@google.com> <20120829170711.GC12504@redhat.com> <20120829171345.GC20312@google.com> <20120830220745.GI27257@redhat.com> <20120831014359.GB15218@moria.home.lan> <20120904034100.GA21602@moria.home.lan> <20120904195156.GE25236@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 11, 2012 at 03:28:57PM -0400, Mikulas Patocka wrote: > > > On Tue, 4 Sep 2012, Kent Overstreet wrote: > > > On Tue, Sep 04, 2012 at 03:26:19PM -0400, Mikulas Patocka wrote: > > > > > > > > > On Mon, 3 Sep 2012, Kent Overstreet wrote: > > > > > > > On Mon, Sep 03, 2012 at 04:41:37PM -0400, Mikulas Patocka wrote: > > > > > ... or another possibility - start a timer when something is put to > > > > > current->bio_list and use that timer to pop entries off current->bio_list > > > > > and submit them to a workqueue. The timer can be cpu-local so only > > > > > interrupt masking is required to synchronize against the timer. > > > > > > > > > > This would normally run just like the current kernel and in case of > > > > > deadlock, the timer would kick in and resolve the deadlock. > > > > > > > > Ugh. That's a _terrible_ idea. > > > > > > > > Remember the old plugging code? You ever have to debug performance > > > > issues caused by it? > > > > > > Yes, I do remember it (and I fixed one bug that resulted in missed unplug > > > and degraded performance). > > > > > > But currently, deadlocks due to exhausted mempools and bios being stalled > > > in current->bio_list don't happen (or do happen below so rarely that they > > > aren't reported). > > > > > > If we add a timer, it will turn a deadlock into an i/o delay, but it can't > > > make things any worse. > > > > This is all true. I'm not arguing your solution wouldn't _work_... I'd > > try and give some real reasoning for my objections but it'll take me > > awhile to figure out how to coherently explain it and I'm very sleep > > deprived. > > > > > Currently, dm targets allocate request-specific data from target-specific > > > mempool. mempools are in dm-crypt, dm-delay, dm-mirror, dm-snapshot, > > > dm-thin, dm-verity. You can change it to allocate request-specific data > > > with the bio. > > > > I wrote a patch for dm_target_io last night. I think I know an easy way > > to go about converting the rest but it'll probably have to wait until > > I'm further along with my immutable bvec stuff. > > > > Completely untested patch below: > > The patch didn't work (it has random allocation failures and crashes when > the device is closed). The patch also contains some unrelated changes. > > I created this patch that does the same thing. Cool! Thanks for finishing this. I like your approach with rolling the bio allocation into alloc_tio() - it solves a problem I was having with the front_pad not being zeroed - but it does prevent the use of bio_clone_bioset(), which is going to cause minor issues with my immutable bvec work. Perhaps bio_alloc_bioset() should just be changed to zero the front_pad, that'd probably be useful elsewhere anyways. You might want to rebase onto Jens' tree, it has my patches that get rid of bi_destructor and the front_pad conversion for request based dm: git://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git for-next > > Mikulas > > --- > Use front pad to allocate dm_target_io > > dm_target_io was previously allocated from a mempool. For each > dm_target_io, there is exactly one bio allocated from a bioset. > > This patch merges these two allocations into one allocating: we create a > bioset with front_pad equal to the size of dm_target_io - so that every > bio allocated from the bioset has sizeof(struct dm_target_io) bytes > before it. We allocate a bio and use the bytes before the bio as > dm_target_io. > > This idea was introdiced by Kent Overstreet > > Signed-off-by: Mikulas Patocka > > --- > drivers/md/dm.c | 96 +++++++++++++++++++++++--------------------------------- > 1 file changed, 41 insertions(+), 55 deletions(-) > > Index: linux-3.5.3-fast/drivers/md/dm.c > =================================================================== > --- linux-3.5.3-fast.orig/drivers/md/dm.c 2012-09-10 16:06:30.000000000 +0200 > +++ linux-3.5.3-fast/drivers/md/dm.c 2012-09-11 19:32:36.000000000 +0200 > @@ -71,6 +71,7 @@ struct dm_target_io { > struct dm_io *io; > struct dm_target *ti; > union map_info info; > + struct bio clone; > }; > > /* > @@ -464,7 +465,9 @@ static void free_io(struct mapped_device > > static void free_tio(struct mapped_device *md, struct dm_target_io *tio) > { > - mempool_free(tio, md->tio_pool); > + tio->clone.bi_private = md->bs; > + tio->clone.bi_end_io = NULL; > + bio_put(&tio->clone); > } > > static struct dm_rq_target_io *alloc_rq_tio(struct mapped_device *md, > @@ -710,13 +713,7 @@ static void clone_endio(struct bio *bio, > } > } > > - /* > - * Store md for cleanup instead of tio which is about to get freed. > - */ > - bio->bi_private = md->bs; > - > free_tio(md, tio); > - bio_put(bio); > dec_pending(io, error); > } > > @@ -1032,12 +1029,12 @@ int dm_set_target_max_io_len(struct dm_t > } > EXPORT_SYMBOL_GPL(dm_set_target_max_io_len); > > -static void __map_bio(struct dm_target *ti, struct bio *clone, > - struct dm_target_io *tio) > +static void __map_bio(struct dm_target *ti, struct dm_target_io *tio) > { > int r; > sector_t sector; > struct mapped_device *md; > + struct bio *clone = &tio->clone; > > clone->bi_end_io = clone_endio; > clone->bi_private = tio; > @@ -1061,12 +1058,6 @@ static void __map_bio(struct dm_target * > /* error the io and bail out, or requeue it if needed */ > md = tio->io->md; > dec_pending(tio->io, r); > - /* > - * Store bio_set for cleanup. > - */ > - clone->bi_end_io = NULL; > - clone->bi_private = md->bs; > - bio_put(clone); > free_tio(md, tio); > } else if (r) { > DMWARN("unimplemented target map return value: %d", r); > @@ -1094,15 +1085,13 @@ static void dm_bio_destructor(struct bio > /* > * Creates a little bio that just does part of a bvec. > */ > -static struct bio *split_bvec(struct bio *bio, sector_t sector, > - unsigned short idx, unsigned int offset, > - unsigned int len, struct bio_set *bs) > +static void split_bvec(struct dm_target_io *tio, struct bio *bio, > + sector_t sector, unsigned short idx, unsigned int offset, > + unsigned int len, struct bio_set *bs) > { > - struct bio *clone; > + struct bio *clone = &tio->clone; > struct bio_vec *bv = bio->bi_io_vec + idx; > > - clone = bio_alloc_bioset(GFP_NOIO, 1, bs); > - clone->bi_destructor = dm_bio_destructor; > *clone->bi_io_vec = *bv; > > clone->bi_sector = sector; > @@ -1119,22 +1108,19 @@ static struct bio *split_bvec(struct bio > bio_integrity_trim(clone, > bio_sector_offset(bio, idx, offset), len); > } > - > - return clone; > } > > /* > * Creates a bio that consists of range of complete bvecs. > */ > -static struct bio *clone_bio(struct bio *bio, sector_t sector, > - unsigned short idx, unsigned short bv_count, > - unsigned int len, struct bio_set *bs) > +static void clone_bio(struct dm_target_io *tio, struct bio *bio, > + sector_t sector, unsigned short idx, > + unsigned short bv_count, unsigned int len, > + struct bio_set *bs) > { > - struct bio *clone; > + struct bio *clone = &tio->clone; > > - clone = bio_alloc_bioset(GFP_NOIO, bio->bi_max_vecs, bs); > __bio_clone(clone, bio); > - clone->bi_destructor = dm_bio_destructor; > clone->bi_sector = sector; > clone->bi_idx = idx; > clone->bi_vcnt = idx + bv_count; > @@ -1148,14 +1134,17 @@ static struct bio *clone_bio(struct bio > bio_integrity_trim(clone, > bio_sector_offset(bio, idx, 0), len); > } > - > - return clone; > } > > static struct dm_target_io *alloc_tio(struct clone_info *ci, > - struct dm_target *ti) > + struct dm_target *ti, int nr_iovecs) > { > - struct dm_target_io *tio = mempool_alloc(ci->md->tio_pool, GFP_NOIO); > + struct dm_target_io *tio; > + struct bio *clone; > + > + clone = bio_alloc_bioset(GFP_NOIO, nr_iovecs, ci->md->bs); > + tio = container_of(clone, struct dm_target_io, clone); > + tio->clone.bi_destructor = dm_bio_destructor; > > tio->io = ci->io; > tio->ti = ti; > @@ -1167,8 +1156,8 @@ static struct dm_target_io *alloc_tio(st > static void __issue_target_request(struct clone_info *ci, struct dm_target *ti, > unsigned request_nr, sector_t len) > { > - struct dm_target_io *tio = alloc_tio(ci, ti); > - struct bio *clone; > + struct dm_target_io *tio = alloc_tio(ci, ti, ci->bio->bi_max_vecs); > + struct bio *clone = &tio->clone; > > tio->info.target_request_nr = request_nr; > > @@ -1177,15 +1166,13 @@ static void __issue_target_request(struc > * ci->bio->bi_max_vecs is BIO_INLINE_VECS anyway, for both flush > * and discard, so no need for concern about wasted bvec allocations. > */ > - clone = bio_alloc_bioset(GFP_NOIO, ci->bio->bi_max_vecs, ci->md->bs); > __bio_clone(clone, ci->bio); > - clone->bi_destructor = dm_bio_destructor; > if (len) { > clone->bi_sector = ci->sector; > clone->bi_size = to_bytes(len); > } > > - __map_bio(ti, clone, tio); > + __map_bio(ti, tio); > } > > static void __issue_target_requests(struct clone_info *ci, struct dm_target *ti, > @@ -1214,14 +1201,13 @@ static int __clone_and_map_empty_flush(s > */ > static void __clone_and_map_simple(struct clone_info *ci, struct dm_target *ti) > { > - struct bio *clone, *bio = ci->bio; > + struct bio *bio = ci->bio; > struct dm_target_io *tio; > > - tio = alloc_tio(ci, ti); > - clone = clone_bio(bio, ci->sector, ci->idx, > - bio->bi_vcnt - ci->idx, ci->sector_count, > - ci->md->bs); > - __map_bio(ti, clone, tio); > + tio = alloc_tio(ci, ti, bio->bi_max_vecs); > + clone_bio(tio, bio, ci->sector, ci->idx, bio->bi_vcnt - ci->idx, > + ci->sector_count, ci->md->bs); > + __map_bio(ti, tio); > ci->sector_count = 0; > } > > @@ -1259,7 +1245,7 @@ static int __clone_and_map_discard(struc > > static int __clone_and_map(struct clone_info *ci) > { > - struct bio *clone, *bio = ci->bio; > + struct bio *bio = ci->bio; > struct dm_target *ti; > sector_t len = 0, max; > struct dm_target_io *tio; > @@ -1299,10 +1285,10 @@ static int __clone_and_map(struct clone_ > len += bv_len; > } > > - tio = alloc_tio(ci, ti); > - clone = clone_bio(bio, ci->sector, ci->idx, i - ci->idx, len, > - ci->md->bs); > - __map_bio(ti, clone, tio); > + tio = alloc_tio(ci, ti, bio->bi_max_vecs); > + clone_bio(tio, bio, ci->sector, ci->idx, i - ci->idx, len, > + ci->md->bs); > + __map_bio(ti, tio); > > ci->sector += len; > ci->sector_count -= len; > @@ -1327,12 +1313,11 @@ static int __clone_and_map(struct clone_ > > len = min(remaining, max); > > - tio = alloc_tio(ci, ti); > - clone = split_bvec(bio, ci->sector, ci->idx, > - bv->bv_offset + offset, len, > - ci->md->bs); > + tio = alloc_tio(ci, ti, 1); > + split_bvec(tio, bio, ci->sector, ci->idx, > + bv->bv_offset + offset, len, ci->md->bs); > > - __map_bio(ti, clone, tio); > + __map_bio(ti, tio); > > ci->sector += len; > ci->sector_count -= len; > @@ -2765,7 +2750,8 @@ struct dm_md_mempools *dm_alloc_md_mempo > if (!pools->tio_pool) > goto free_io_pool_and_out; > > - pools->bs = bioset_create(pool_size, 0); > + pools->bs = bioset_create(pool_size, (type == DM_TYPE_BIO_BASED) ? > + offsetof(struct dm_target_io, clone) : 0); > if (!pools->bs) > goto free_tio_pool_and_out; >