On Tue, 11 Sep 2012, Kent Overstreet wrote: > 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 This is the patch based on this tree. 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 <koverstreet@xxxxxxxxxx> Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx> --- drivers/md/dm.c | 80 ++++++++++++++++++++++++++------------------------------ 1 file changed, 38 insertions(+), 42 deletions(-) Index: linux-block-copy/drivers/md/dm.c =================================================================== --- linux-block-copy.orig/drivers/md/dm.c 2012-09-12 21:04:34.000000000 +0200 +++ linux-block-copy/drivers/md/dm.c 2012-09-12 21:07:09.000000000 +0200 @@ -71,6 +71,7 @@ struct dm_target_io { struct dm_io *io; struct dm_target *ti; union map_info info; + struct bio clone; }; /* @@ -474,7 +475,7 @@ 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); + bio_put(&tio->clone); } static struct dm_rq_target_io *alloc_rq_tio(struct mapped_device *md, @@ -711,7 +712,6 @@ static void clone_endio(struct bio *bio, } free_tio(md, tio); - bio_put(bio); dec_pending(io, error); } @@ -1027,12 +1027,12 @@ 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; @@ -1056,7 +1056,6 @@ 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); - bio_put(clone); free_tio(md, tio); } else if (r) { DMWARN("unimplemented target map return value: %d", r); @@ -1077,14 +1076,13 @@ struct clone_info { /* * 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_io_vec = *bv; clone->bi_sector = sector; @@ -1101,20 +1099,18 @@ 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_sector = sector; clone->bi_idx = idx; @@ -1129,14 +1125,16 @@ 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->io = ci->io; tio->ti = ti; @@ -1148,8 +1146,8 @@ 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; @@ -1158,14 +1156,13 @@ 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_clone_bioset(ci->bio, GFP_NOIO, ci->md->bs); 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, @@ -1194,14 +1191,13 @@ 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; } @@ -1239,7 +1235,7 @@ 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; @@ -1279,10 +1275,10 @@ 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; @@ -1307,12 +1303,11 @@ 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; @@ -2733,7 +2728,8 @@ struct dm_md_mempools *dm_alloc_md_mempo goto free_io_pool_and_out; pools->bs = (type == DM_TYPE_BIO_BASED) ? - bioset_create(pool_size, 0) : + bioset_create(pool_size, + offsetof(struct dm_target_io, clone)) : bioset_create(pool_size, offsetof(struct dm_rq_clone_bio_info, clone)); 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