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: commit 8754349145edfc791450d3ad54c19f0f3715c86c Author: Kent Overstreet <koverstreet@xxxxxxxxxx> Date: Tue Sep 4 06:17:56 2012 -0700 dm: Use bioset's front_pad for dm_target_io diff --git a/drivers/md/dm.c b/drivers/md/dm.c index f2eb730..3cf39b0 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -71,6 +71,7 @@ struct dm_target_io { struct dm_io *io; struct dm_target *ti; union map_info info; + struct bio clone; }; /* @@ -174,7 +175,7 @@ struct mapped_device { * io objects are allocated from here. */ mempool_t *io_pool; - mempool_t *tio_pool; + mempool_t *rq_tio_pool; struct bio_set *bs; @@ -214,15 +215,8 @@ struct dm_md_mempools { #define MIN_IOS 256 static struct kmem_cache *_io_cache; -static struct kmem_cache *_tio_cache; static struct kmem_cache *_rq_tio_cache; -/* - * Unused now, and needs to be deleted. But since io_pool is overloaded and it's - * still used for _io_cache, I'm leaving this for a later cleanup - */ -static struct kmem_cache *_rq_bio_info_cache; - static int __init local_init(void) { int r = -ENOMEM; @@ -232,22 +226,13 @@ static int __init local_init(void) if (!_io_cache) return r; - /* allocate a slab for the target ios */ - _tio_cache = KMEM_CACHE(dm_target_io, 0); - if (!_tio_cache) - goto out_free_io_cache; - _rq_tio_cache = KMEM_CACHE(dm_rq_target_io, 0); if (!_rq_tio_cache) - goto out_free_tio_cache; - - _rq_bio_info_cache = KMEM_CACHE(dm_rq_clone_bio_info, 0); - if (!_rq_bio_info_cache) - goto out_free_rq_tio_cache; + goto out_free_io_cache; r = dm_uevent_init(); if (r) - goto out_free_rq_bio_info_cache; + goto out_free_rq_tio_cache; _major = major; r = register_blkdev(_major, _name); @@ -261,12 +246,8 @@ static int __init local_init(void) out_uevent_exit: dm_uevent_exit(); -out_free_rq_bio_info_cache: - kmem_cache_destroy(_rq_bio_info_cache); out_free_rq_tio_cache: kmem_cache_destroy(_rq_tio_cache); -out_free_tio_cache: - kmem_cache_destroy(_tio_cache); out_free_io_cache: kmem_cache_destroy(_io_cache); @@ -275,9 +256,7 @@ out_free_io_cache: static void local_exit(void) { - kmem_cache_destroy(_rq_bio_info_cache); kmem_cache_destroy(_rq_tio_cache); - kmem_cache_destroy(_tio_cache); kmem_cache_destroy(_io_cache); unregister_blkdev(_major, _name); dm_uevent_exit(); @@ -461,20 +440,15 @@ static void free_io(struct mapped_device *md, struct dm_io *io) mempool_free(io, md->io_pool); } -static void free_tio(struct mapped_device *md, struct dm_target_io *tio) -{ - mempool_free(tio, md->tio_pool); -} - static struct dm_rq_target_io *alloc_rq_tio(struct mapped_device *md, gfp_t gfp_mask) { - return mempool_alloc(md->tio_pool, gfp_mask); + return mempool_alloc(md->rq_tio_pool, gfp_mask); } static void free_rq_tio(struct dm_rq_target_io *tio) { - mempool_free(tio, tio->md->tio_pool); + mempool_free(tio, tio->md->rq_tio_pool); } static int md_in_flight(struct mapped_device *md) @@ -658,7 +632,6 @@ static void clone_endio(struct bio *bio, int error) int r = 0; struct dm_target_io *tio = bio->bi_private; struct dm_io *io = tio->io; - struct mapped_device *md = tio->io->md; dm_endio_fn endio = tio->ti->type->end_io; if (!bio_flagged(bio, BIO_UPTODATE) && !error) @@ -681,7 +654,6 @@ static void clone_endio(struct bio *bio, int error) } } - free_tio(md, tio); bio_put(bio); dec_pending(io, error); } @@ -998,13 +970,16 @@ int dm_set_target_max_io_len(struct dm_target *ti, sector_t len) } 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_io *io, struct dm_target *ti, struct bio *clone) { + struct dm_target_io *tio = container_of(clone, struct dm_target_io, clone); int r; sector_t sector; struct mapped_device *md; + tio->io = io; + tio->ti = ti; + clone->bi_end_io = clone_endio; clone->bi_private = tio; @@ -1028,7 +1003,6 @@ static void __map_bio(struct dm_target *ti, struct bio *clone, 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); BUG(); @@ -1104,26 +1078,18 @@ static struct bio *clone_bio(struct bio *bio, sector_t sector, return clone; } -static struct dm_target_io *alloc_tio(struct clone_info *ci, - struct dm_target *ti) +static void init_tio(struct bio *bio) { - struct dm_target_io *tio = mempool_alloc(ci->md->tio_pool, GFP_NOIO); - - tio->io = ci->io; - tio->ti = ti; + struct dm_target_io *tio = container_of(bio, struct dm_target_io, clone); memset(&tio->info, 0, sizeof(tio->info)); - - return tio; } 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 dm_target_io *tio; struct bio *clone; - tio->info.target_request_nr = request_nr; - /* * Discard requests require the bio's inline iovecs be initialized. * ci->bio->bi_max_vecs is BIO_INLINE_VECS anyway, for both flush @@ -1136,7 +1102,10 @@ static void __issue_target_request(struct clone_info *ci, struct dm_target *ti, clone->bi_size = to_bytes(len); } - __map_bio(ti, clone, tio); + tio = container_of(clone, struct dm_target_io, clone); + tio->info.target_request_nr = request_nr; + + __map_bio(ci->io, ti, clone); } static void __issue_target_requests(struct clone_info *ci, struct dm_target *ti, @@ -1166,13 +1135,13 @@ static int __clone_and_map_empty_flush(struct clone_info *ci) static void __clone_and_map_simple(struct clone_info *ci, struct dm_target *ti) { struct bio *clone, *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); + + init_tio(clone); + __map_bio(ci->io, ti, clone); ci->sector_count = 0; } @@ -1213,7 +1182,6 @@ static int __clone_and_map(struct clone_info *ci) struct bio *clone, *bio = ci->bio; struct dm_target *ti; sector_t len = 0, max; - struct dm_target_io *tio; if (unlikely(bio->bi_rw & REQ_DISCARD)) return __clone_and_map_discard(ci); @@ -1250,10 +1218,11 @@ static int __clone_and_map(struct clone_info *ci) 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); + + init_tio(clone); + __map_bio(ci->io, ti, clone); ci->sector += len; ci->sector_count -= len; @@ -1278,12 +1247,12 @@ static int __clone_and_map(struct clone_info *ci) 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); - __map_bio(ti, clone, tio); + init_tio(clone); + __map_bio(ci->io, ti, clone); ci->sector += len; ci->sector_count -= len; @@ -1911,8 +1880,8 @@ static void free_dev(struct mapped_device *md) unlock_fs(md); bdput(md->bdev); destroy_workqueue(md->wq); - if (md->tio_pool) - mempool_destroy(md->tio_pool); + if (md->rq_tio_pool) + mempool_destroy(md->rq_tio_pool); if (md->io_pool) mempool_destroy(md->io_pool); if (md->bs) @@ -1935,16 +1904,16 @@ static void __bind_mempools(struct mapped_device *md, struct dm_table *t) { struct dm_md_mempools *p; - if (md->io_pool && md->tio_pool && md->bs) + if ((md->io_pool || md->rq_tio_pool) && md->bs) /* the md already has necessary mempools */ goto out; p = dm_table_get_md_mempools(t); - BUG_ON(!p || md->io_pool || md->tio_pool || md->bs); + BUG_ON(!p || md->io_pool || md->rq_tio_pool || md->bs); md->io_pool = p->io_pool; p->io_pool = NULL; - md->tio_pool = p->tio_pool; + md->rq_tio_pool = p->tio_pool; p->tio_pool = NULL; md->bs = p->bs; p->bs = NULL; @@ -2693,40 +2662,29 @@ struct dm_md_mempools *dm_alloc_md_mempools(unsigned type, unsigned integrity) if (!pools) return NULL; - pools->io_pool = (type == DM_TYPE_BIO_BASED) ? - mempool_create_slab_pool(MIN_IOS, _io_cache) : - mempool_create_slab_pool(MIN_IOS, _rq_bio_info_cache); + if (type == DM_TYPE_BIO_BASED) + pools->io_pool = mempool_create_slab_pool(MIN_IOS, _io_cache); if (!pools->io_pool) - goto free_pools_and_out; + goto err; - pools->tio_pool = (type == DM_TYPE_BIO_BASED) ? - mempool_create_slab_pool(MIN_IOS, _tio_cache) : - mempool_create_slab_pool(MIN_IOS, _rq_tio_cache); + if (type == DM_TYPE_REQUEST_BASED) + pools->tio_pool = + mempool_create_slab_pool(MIN_IOS, _rq_tio_cache); if (!pools->tio_pool) - goto free_io_pool_and_out; + goto err; pools->bs = bioset_create(pool_size, - offsetof(struct dm_rq_clone_bio_info, clone)); + max(offsetof(struct dm_target_io, clone), + offsetof(struct dm_rq_clone_bio_info, clone))); if (!pools->bs) - goto free_tio_pool_and_out; + goto err; if (integrity && bioset_integrity_create(pools->bs, pool_size)) - goto free_bioset_and_out; + goto err; return pools; - -free_bioset_and_out: - bioset_free(pools->bs); - -free_tio_pool_and_out: - mempool_destroy(pools->tio_pool); - -free_io_pool_and_out: - mempool_destroy(pools->io_pool); - -free_pools_and_out: - kfree(pools); - +err: + dm_free_md_mempools(pools); return NULL; } -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel