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dm cache: simplify deferred set reference count increments
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Factor out inc_and_issue and inc_ds helpers to simplify deferred set
reference count increments.  Also cleanup cache_map to consistently call
cell_defer and inc_ds when the bio is DM_MAPIO_REMAPPED.

No functional change.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
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Joe Thornber authored and Mike Snitzer committed Aug 1, 2014
1 parent e5aea7b commit 8c081b5
Showing 1 changed file with 77 additions and 46 deletions.
123 changes: 77 additions & 46 deletions drivers/md/dm-cache-target.c
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Original file line number Diff line number Diff line change
Expand Up @@ -718,6 +718,22 @@ static int bio_triggers_commit(struct cache *cache, struct bio *bio)
return bio->bi_rw & (REQ_FLUSH | REQ_FUA);
}

/*
* You must increment the deferred set whilst the prison cell is held. To
* encourage this, we ask for 'cell' to be passed in.
*/
static void inc_ds(struct cache *cache, struct bio *bio,
struct dm_bio_prison_cell *cell)
{
size_t pb_data_size = get_per_bio_data_size(cache);
struct per_bio_data *pb = get_per_bio_data(bio, pb_data_size);

BUG_ON(!cell);
BUG_ON(pb->all_io_entry);

pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
}

static void issue(struct cache *cache, struct bio *bio)
{
unsigned long flags;
Expand All @@ -737,6 +753,12 @@ static void issue(struct cache *cache, struct bio *bio)
spin_unlock_irqrestore(&cache->lock, flags);
}

static void inc_and_issue(struct cache *cache, struct bio *bio, struct dm_bio_prison_cell *cell)
{
inc_ds(cache, bio, cell);
issue(cache, bio);
}

static void defer_writethrough_bio(struct cache *cache, struct bio *bio)
{
unsigned long flags;
Expand Down Expand Up @@ -1015,6 +1037,11 @@ static void issue_overwrite(struct dm_cache_migration *mg, struct bio *bio)

dm_hook_bio(&pb->hook_info, bio, overwrite_endio, mg);
remap_to_cache_dirty(mg->cache, bio, mg->new_oblock, mg->cblock);

/*
* No need to inc_ds() here, since the cell will be held for the
* duration of the io.
*/
generic_make_request(bio);
}

Expand Down Expand Up @@ -1115,8 +1142,7 @@ static void check_for_quiesced_migrations(struct cache *cache,
return;

INIT_LIST_HEAD(&work);
if (pb->all_io_entry)
dm_deferred_entry_dec(pb->all_io_entry, &work);
dm_deferred_entry_dec(pb->all_io_entry, &work);

if (!list_empty(&work))
queue_quiesced_migrations(cache, &work);
Expand Down Expand Up @@ -1252,6 +1278,11 @@ static void process_flush_bio(struct cache *cache, struct bio *bio)
else
remap_to_cache(cache, bio, 0);

/*
* REQ_FLUSH is not directed at any particular block so we don't
* need to inc_ds(). REQ_FUA's are split into a write + REQ_FLUSH
* by dm-core.
*/
issue(cache, bio);
}

Expand Down Expand Up @@ -1301,15 +1332,6 @@ static void inc_miss_counter(struct cache *cache, struct bio *bio)
&cache->stats.read_miss : &cache->stats.write_miss);
}

static void issue_cache_bio(struct cache *cache, struct bio *bio,
struct per_bio_data *pb,
dm_oblock_t oblock, dm_cblock_t cblock)
{
pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
remap_to_cache_dirty(cache, bio, oblock, cblock);
issue(cache, bio);
}

static void process_bio(struct cache *cache, struct prealloc *structs,
struct bio *bio)
{
Expand All @@ -1318,8 +1340,6 @@ static void process_bio(struct cache *cache, struct prealloc *structs,
dm_oblock_t block = get_bio_block(cache, bio);
struct dm_bio_prison_cell *cell_prealloc, *old_ocell, *new_ocell;
struct policy_result lookup_result;
size_t pb_data_size = get_per_bio_data_size(cache);
struct per_bio_data *pb = get_per_bio_data(bio, pb_data_size);
bool discarded_block = is_discarded_oblock(cache, block);
bool passthrough = passthrough_mode(&cache->features);
bool can_migrate = !passthrough && (discarded_block || spare_migration_bandwidth(cache));
Expand Down Expand Up @@ -1359,30 +1379,30 @@ static void process_bio(struct cache *cache, struct prealloc *structs,

} else {
/* FIXME: factor out issue_origin() */
pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
remap_to_origin_clear_discard(cache, bio, block);
issue(cache, bio);
inc_and_issue(cache, bio, new_ocell);
}
} else {
inc_hit_counter(cache, bio);

if (bio_data_dir(bio) == WRITE &&
writethrough_mode(&cache->features) &&
!is_dirty(cache, lookup_result.cblock)) {
pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
remap_to_origin_then_cache(cache, bio, block, lookup_result.cblock);
issue(cache, bio);
} else
issue_cache_bio(cache, bio, pb, block, lookup_result.cblock);
inc_and_issue(cache, bio, new_ocell);

} else {
remap_to_cache_dirty(cache, bio, block, lookup_result.cblock);
inc_and_issue(cache, bio, new_ocell);
}
}

break;

case POLICY_MISS:
inc_miss_counter(cache, bio);
pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
remap_to_origin_clear_discard(cache, bio, block);
issue(cache, bio);
inc_and_issue(cache, bio, new_ocell);
break;

case POLICY_NEW:
Expand Down Expand Up @@ -1501,6 +1521,9 @@ static void process_deferred_flush_bios(struct cache *cache, bool submit_bios)
bio_list_init(&cache->deferred_flush_bios);
spin_unlock_irqrestore(&cache->lock, flags);

/*
* These bios have already been through inc_ds()
*/
while ((bio = bio_list_pop(&bios)))
submit_bios ? generic_make_request(bio) : bio_io_error(bio);
}
Expand All @@ -1518,6 +1541,9 @@ static void process_deferred_writethrough_bios(struct cache *cache)
bio_list_init(&cache->deferred_writethrough_bios);
spin_unlock_irqrestore(&cache->lock, flags);

/*
* These bios have already been through inc_ds()
*/
while ((bio = bio_list_pop(&bios)))
generic_make_request(bio);
}
Expand Down Expand Up @@ -2406,16 +2432,13 @@ static int cache_ctr(struct dm_target *ti, unsigned argc, char **argv)
return r;
}

static int cache_map(struct dm_target *ti, struct bio *bio)
static int __cache_map(struct cache *cache, struct bio *bio, struct dm_bio_prison_cell **cell)
{
struct cache *cache = ti->private;

int r;
dm_oblock_t block = get_bio_block(cache, bio);
size_t pb_data_size = get_per_bio_data_size(cache);
bool can_migrate = false;
bool discarded_block;
struct dm_bio_prison_cell *cell;
struct policy_result lookup_result;
struct per_bio_data *pb = init_per_bio_data(bio, pb_data_size);

Expand All @@ -2437,15 +2460,15 @@ static int cache_map(struct dm_target *ti, struct bio *bio)
/*
* Check to see if that block is currently migrating.
*/
cell = alloc_prison_cell(cache);
if (!cell) {
*cell = alloc_prison_cell(cache);
if (!*cell) {
defer_bio(cache, bio);
return DM_MAPIO_SUBMITTED;
}

r = bio_detain(cache, block, bio, cell,
r = bio_detain(cache, block, bio, *cell,
(cell_free_fn) free_prison_cell,
cache, &cell);
cache, cell);
if (r) {
if (r < 0)
defer_bio(cache, bio);
Expand All @@ -2458,11 +2481,12 @@ static int cache_map(struct dm_target *ti, struct bio *bio)
r = policy_map(cache->policy, block, false, can_migrate, discarded_block,
bio, &lookup_result);
if (r == -EWOULDBLOCK) {
cell_defer(cache, cell, true);
cell_defer(cache, *cell, true);
return DM_MAPIO_SUBMITTED;

} else if (r) {
DMERR_LIMIT("Unexpected return from cache replacement policy: %d", r);
cell_defer(cache, *cell, false);
bio_io_error(bio);
return DM_MAPIO_SUBMITTED;
}
Expand All @@ -2476,59 +2500,66 @@ static int cache_map(struct dm_target *ti, struct bio *bio)
* We need to invalidate this block, so
* defer for the worker thread.
*/
cell_defer(cache, cell, true);
cell_defer(cache, *cell, true);
r = DM_MAPIO_SUBMITTED;

} else {
pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
inc_miss_counter(cache, bio);
remap_to_origin_clear_discard(cache, bio, block);

cell_defer(cache, cell, false);
}

} else {
inc_hit_counter(cache, bio);
pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);

if (bio_data_dir(bio) == WRITE && writethrough_mode(&cache->features) &&
!is_dirty(cache, lookup_result.cblock))
remap_to_origin_then_cache(cache, bio, block, lookup_result.cblock);
else
remap_to_cache_dirty(cache, bio, block, lookup_result.cblock);

cell_defer(cache, cell, false);
}
break;

case POLICY_MISS:
inc_miss_counter(cache, bio);
pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);

if (pb->req_nr != 0) {
/*
* This is a duplicate writethrough io that is no
* longer needed because the block has been demoted.
*/
bio_endio(bio, 0);
cell_defer(cache, cell, false);
return DM_MAPIO_SUBMITTED;
} else {
cell_defer(cache, *cell, false);
r = DM_MAPIO_SUBMITTED;

} else
remap_to_origin_clear_discard(cache, bio, block);
cell_defer(cache, cell, false);
}

break;

default:
DMERR_LIMIT("%s: erroring bio: unknown policy op: %u", __func__,
(unsigned) lookup_result.op);
cell_defer(cache, *cell, false);
bio_io_error(bio);
r = DM_MAPIO_SUBMITTED;
}

return r;
}

static int cache_map(struct dm_target *ti, struct bio *bio)
{
int r;
struct dm_bio_prison_cell *cell;
struct cache *cache = ti->private;

r = __cache_map(cache, bio, &cell);
if (r == DM_MAPIO_REMAPPED) {
inc_ds(cache, bio, cell);
cell_defer(cache, cell, false);
}

return r;
}

static int cache_end_io(struct dm_target *ti, struct bio *bio, int error)
{
struct cache *cache = ti->private;
Expand Down Expand Up @@ -3072,7 +3103,7 @@ static void cache_io_hints(struct dm_target *ti, struct queue_limits *limits)

static struct target_type cache_target = {
.name = "cache",
.version = {1, 4, 0},
.version = {1, 5, 0},
.module = THIS_MODULE,
.ctr = cache_ctr,
.dtr = cache_dtr,
Expand Down

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