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dm thin: prepare to support discard
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This patch contains the ground work needed for dm-thin to support discard.

  - Adds endio function that replaces shared_read_endio.

  - Introduce an explicit 'quiesced' flag into the new_mapping structure.
    Before, this was implicitly indicated by m->list being empty.

  - The map_info->ptr remains constant for the duration of a bio's trip
    through the thin target.  Make it easier to reason about it.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
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Joe Thornber authored and Alasdair G Kergon committed Mar 28, 2012
1 parent 6efd6e8 commit eb2aa48
Showing 1 changed file with 72 additions and 53 deletions.
125 changes: 72 additions & 53 deletions drivers/md/dm-thin.c
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Original file line number Diff line number Diff line change
Expand Up @@ -523,7 +523,7 @@ struct pool {

struct bio_list retry_on_resume_list;

struct deferred_set ds; /* FIXME: move to thin_c */
struct deferred_set shared_read_ds;

struct new_mapping *next_mapping;
mempool_t *mapping_pool;
Expand Down Expand Up @@ -618,6 +618,12 @@ static struct pool *__pool_table_lookup_metadata_dev(struct block_device *md_dev

/*----------------------------------------------------------------*/

struct endio_hook {
struct thin_c *tc;
struct deferred_entry *shared_read_entry;
struct new_mapping *overwrite_mapping;
};

static void __requeue_bio_list(struct thin_c *tc, struct bio_list *master)
{
struct bio *bio;
Expand All @@ -628,7 +634,8 @@ static void __requeue_bio_list(struct thin_c *tc, struct bio_list *master)
bio_list_init(master);

while ((bio = bio_list_pop(&bios))) {
if (dm_get_mapinfo(bio)->ptr == tc)
struct endio_hook *h = dm_get_mapinfo(bio)->ptr;
if (h->tc == tc)
bio_endio(bio, DM_ENDIO_REQUEUE);
else
bio_list_add(master, bio);
Expand Down Expand Up @@ -716,16 +723,11 @@ static void wake_worker(struct pool *pool)
/*
* Bio endio functions.
*/
struct endio_hook {
struct thin_c *tc;
bio_end_io_t *saved_bi_end_io;
struct deferred_entry *entry;
};

struct new_mapping {
struct list_head list;

int prepared;
unsigned quiesced:1;
unsigned prepared:1;

struct thin_c *tc;
dm_block_t virt_block;
Expand All @@ -747,7 +749,7 @@ static void __maybe_add_mapping(struct new_mapping *m)
{
struct pool *pool = m->tc->pool;

if (list_empty(&m->list) && m->prepared) {
if (m->quiesced && m->prepared) {
list_add(&m->list, &pool->prepared_mappings);
wake_worker(pool);
}
Expand All @@ -770,7 +772,8 @@ static void copy_complete(int read_err, unsigned long write_err, void *context)
static void overwrite_endio(struct bio *bio, int err)
{
unsigned long flags;
struct new_mapping *m = dm_get_mapinfo(bio)->ptr;
struct endio_hook *h = dm_get_mapinfo(bio)->ptr;
struct new_mapping *m = h->overwrite_mapping;
struct pool *pool = m->tc->pool;

m->err = err;
Expand All @@ -781,31 +784,6 @@ static void overwrite_endio(struct bio *bio, int err)
spin_unlock_irqrestore(&pool->lock, flags);
}

static void shared_read_endio(struct bio *bio, int err)
{
struct list_head mappings;
struct new_mapping *m, *tmp;
struct endio_hook *h = dm_get_mapinfo(bio)->ptr;
unsigned long flags;
struct pool *pool = h->tc->pool;

bio->bi_end_io = h->saved_bi_end_io;
bio_endio(bio, err);

INIT_LIST_HEAD(&mappings);
ds_dec(h->entry, &mappings);

spin_lock_irqsave(&pool->lock, flags);
list_for_each_entry_safe(m, tmp, &mappings, list) {
list_del(&m->list);
INIT_LIST_HEAD(&m->list);
__maybe_add_mapping(m);
}
spin_unlock_irqrestore(&pool->lock, flags);

mempool_free(h, pool->endio_hook_pool);
}

/*----------------------------------------------------------------*/

/*
Expand Down Expand Up @@ -957,6 +935,7 @@ static void schedule_copy(struct thin_c *tc, dm_block_t virt_block,
struct new_mapping *m = get_next_mapping(pool);

INIT_LIST_HEAD(&m->list);
m->quiesced = 0;
m->prepared = 0;
m->tc = tc;
m->virt_block = virt_block;
Expand All @@ -965,7 +944,8 @@ static void schedule_copy(struct thin_c *tc, dm_block_t virt_block,
m->err = 0;
m->bio = NULL;

ds_add_work(&pool->ds, &m->list);
if (!ds_add_work(&pool->shared_read_ds, &m->list))
m->quiesced = 1;

/*
* IO to pool_dev remaps to the pool target's data_dev.
Expand All @@ -974,9 +954,10 @@ static void schedule_copy(struct thin_c *tc, dm_block_t virt_block,
* bio immediately. Otherwise we use kcopyd to clone the data first.
*/
if (io_overwrites_block(pool, bio)) {
struct endio_hook *h = dm_get_mapinfo(bio)->ptr;
h->overwrite_mapping = m;
m->bio = bio;
save_and_set_endio(bio, &m->saved_bi_end_io, overwrite_endio);
dm_get_mapinfo(bio)->ptr = m;
remap_and_issue(tc, bio, data_dest);
} else {
struct dm_io_region from, to;
Expand Down Expand Up @@ -1023,6 +1004,7 @@ static void schedule_zero(struct thin_c *tc, dm_block_t virt_block,
struct new_mapping *m = get_next_mapping(pool);

INIT_LIST_HEAD(&m->list);
m->quiesced = 1;
m->prepared = 0;
m->tc = tc;
m->virt_block = virt_block;
Expand All @@ -1040,9 +1022,10 @@ static void schedule_zero(struct thin_c *tc, dm_block_t virt_block,
process_prepared_mapping(m);

else if (io_overwrites_block(pool, bio)) {
struct endio_hook *h = dm_get_mapinfo(bio)->ptr;
h->overwrite_mapping = m;
m->bio = bio;
save_and_set_endio(bio, &m->saved_bi_end_io, overwrite_endio);
dm_get_mapinfo(bio)->ptr = m;
remap_and_issue(tc, bio, data_block);

} else {
Expand Down Expand Up @@ -1129,7 +1112,8 @@ static int alloc_data_block(struct thin_c *tc, dm_block_t *result)
*/
static void retry_on_resume(struct bio *bio)
{
struct thin_c *tc = dm_get_mapinfo(bio)->ptr;
struct endio_hook *h = dm_get_mapinfo(bio)->ptr;
struct thin_c *tc = h->tc;
struct pool *pool = tc->pool;
unsigned long flags;

Expand Down Expand Up @@ -1195,13 +1179,9 @@ static void process_shared_bio(struct thin_c *tc, struct bio *bio,
if (bio_data_dir(bio) == WRITE)
break_sharing(tc, bio, block, &key, lookup_result, cell);
else {
struct endio_hook *h;
h = mempool_alloc(pool->endio_hook_pool, GFP_NOIO);
struct endio_hook *h = dm_get_mapinfo(bio)->ptr;

h->tc = tc;
h->entry = ds_inc(&pool->ds);
save_and_set_endio(bio, &h->saved_bi_end_io, shared_read_endio);
dm_get_mapinfo(bio)->ptr = h;
h->shared_read_entry = ds_inc(&pool->shared_read_ds);

cell_release_singleton(cell, bio);
remap_and_issue(tc, bio, lookup_result->block);
Expand Down Expand Up @@ -1325,7 +1305,9 @@ static void process_deferred_bios(struct pool *pool)
spin_unlock_irqrestore(&pool->lock, flags);

while ((bio = bio_list_pop(&bios))) {
struct thin_c *tc = dm_get_mapinfo(bio)->ptr;
struct endio_hook *h = dm_get_mapinfo(bio)->ptr;
struct thin_c *tc = h->tc;

/*
* If we've got no free new_mapping structs, and processing
* this bio might require one, we pause until there are some
Expand Down Expand Up @@ -1408,6 +1390,18 @@ static void thin_defer_bio(struct thin_c *tc, struct bio *bio)
wake_worker(pool);
}

static struct endio_hook *thin_hook_bio(struct thin_c *tc, struct bio *bio)
{
struct pool *pool = tc->pool;
struct endio_hook *h = mempool_alloc(pool->endio_hook_pool, GFP_NOIO);

h->tc = tc;
h->shared_read_entry = NULL;
h->overwrite_mapping = NULL;

return h;
}

/*
* Non-blocking function called from the thin target's map function.
*/
Expand All @@ -1420,11 +1414,7 @@ static int thin_bio_map(struct dm_target *ti, struct bio *bio,
struct dm_thin_device *td = tc->td;
struct dm_thin_lookup_result result;

/*
* Save the thin context for easy access from the deferred bio later.
*/
map_context->ptr = tc;

map_context->ptr = thin_hook_bio(tc, bio);
if (bio->bi_rw & (REQ_FLUSH | REQ_FUA)) {
thin_defer_bio(tc, bio);
return DM_MAPIO_SUBMITTED;
Expand Down Expand Up @@ -1604,7 +1594,7 @@ static struct pool *pool_create(struct mapped_device *pool_md,
pool->low_water_triggered = 0;
pool->no_free_space = 0;
bio_list_init(&pool->retry_on_resume_list);
ds_init(&pool->ds);
ds_init(&pool->shared_read_ds);

pool->next_mapping = NULL;
pool->mapping_pool =
Expand Down Expand Up @@ -2394,6 +2384,34 @@ static int thin_map(struct dm_target *ti, struct bio *bio,
return thin_bio_map(ti, bio, map_context);
}

static int thin_endio(struct dm_target *ti,
struct bio *bio, int err,
union map_info *map_context)
{
unsigned long flags;
struct endio_hook *h = map_context->ptr;
struct list_head work;
struct new_mapping *m, *tmp;
struct pool *pool = h->tc->pool;

if (h->shared_read_entry) {
INIT_LIST_HEAD(&work);
ds_dec(h->shared_read_entry, &work);

spin_lock_irqsave(&pool->lock, flags);
list_for_each_entry_safe(m, tmp, &work, list) {
list_del(&m->list);
m->quiesced = 1;
__maybe_add_mapping(m);
}
spin_unlock_irqrestore(&pool->lock, flags);
}

mempool_free(h, pool->endio_hook_pool);

return 0;
}

static void thin_postsuspend(struct dm_target *ti)
{
if (dm_noflush_suspending(ti))
Expand Down Expand Up @@ -2481,6 +2499,7 @@ static struct target_type thin_target = {
.ctr = thin_ctr,
.dtr = thin_dtr,
.map = thin_map,
.end_io = thin_endio,
.postsuspend = thin_postsuspend,
.status = thin_status,
.iterate_devices = thin_iterate_devices,
Expand Down

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