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-   -   dm thin: add discard pool features (http://www.linux-archive.org/device-mapper-development/639040-dm-thin-add-discard-pool-features.html)

Mike Snitzer 02-29-2012 01:50 PM

dm thin: add discard pool features
 
From: Joe Thornber <ejt@redhat.com>

Make additional features available during pool creation:

'skip_discard': disable discard support
'skip_discard_passdown': don't pass discards down to the underlying data device

Signed-off-by: Joe Thornber <ejt@redhat.com>
Acked-by: Mike Snitzer <snitzer@redhat.com>
---
Documentation/device-mapper/thin-provisioning.txt | 2 +
drivers/md/dm-thin.c | 79 +++++++++++++++------
2 files changed, 59 insertions(+), 22 deletions(-)

diff --git a/Documentation/device-mapper/thin-provisioning.txt b/Documentation/device-mapper/thin-provisioning.txt
index 13e42fb..57076dd 100644
--- a/Documentation/device-mapper/thin-provisioning.txt
+++ b/Documentation/device-mapper/thin-provisioning.txt
@@ -222,6 +222,8 @@ i) Constructor

Optional feature arguments:
- 'skip_block_zeroing': skips the zeroing of newly-provisioned blocks.
+ 'skip_discard': disable discard support
+ 'skip_discard_passdown': don't pass discards down to the underlying data device

Data block size must be between 64KB (128 sectors) and 1GB
(2097152 sectors) inclusive.
diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index fec7ddb..2e16b3a 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -500,6 +500,13 @@ static void build_virtual_key(struct dm_thin_device *td, dm_block_t b,
* devices.
*/
struct new_mapping;
+
+struct pool_features {
+ unsigned zero_new_blocks:1;
+ unsigned discard_enabled:1;
+ unsigned discard_passdown:1;
+};
+
struct pool {
struct list_head list;
struct dm_target *ti; /* Only set if a pool target is bound */
@@ -513,7 +520,7 @@ struct pool {
dm_block_t offset_mask;
dm_block_t low_water_blocks;

- unsigned zero_new_blocks:1;
+ struct pool_features pf;
unsigned low_water_triggered:1; /* A dm event has been sent */
unsigned no_free_space:1; /* A -ENOSPC warning has been issued */

@@ -554,7 +561,7 @@ struct pool_c {
struct dm_target_callbacks callbacks;

dm_block_t low_water_blocks;
- unsigned zero_new_blocks:1;
+ struct pool_features pf;
};

/*
@@ -1060,7 +1067,7 @@ static void schedule_zero(struct thin_c *tc, dm_block_t virt_block,
* zeroing pre-existing data, we can issue the bio immediately.
* Otherwise we use kcopyd to zero the data first.
*/
- if (!pool->zero_new_blocks)
+ if (!pool->pf.zero_new_blocks)
process_prepared_mapping(m);

else if (io_overwrites_block(pool, bio)) {
@@ -1626,7 +1633,7 @@ static int bind_control_target(struct pool *pool, struct dm_target *ti)

pool->ti = ti;
pool->low_water_blocks = pt->low_water_blocks;
- pool->zero_new_blocks = pt->zero_new_blocks;
+ pool->pf = pt->pf;

return 0;
}
@@ -1640,6 +1647,14 @@ static void unbind_control_target(struct pool *pool, struct dm_target *ti)
/*----------------------------------------------------------------
* Pool creation
*--------------------------------------------------------------*/
+/* Initialize pool features. */
+static void pool_features_init(struct pool_features *pf)
+{
+ pf->zero_new_blocks = 1;
+ pf->discard_enabled = 1;
+ pf->discard_passdown = 1;
+}
+
static void __pool_destroy(struct pool *pool)
{
__pool_table_remove(pool);
@@ -1687,7 +1702,7 @@ static struct pool *pool_create(struct mapped_device *pool_md,
pool->block_shift = ffs(block_size) - 1;
pool->offset_mask = block_size - 1;
pool->low_water_blocks = 0;
- pool->zero_new_blocks = 1;
+ pool_features_init(&pool->pf);
pool->prison = prison_create(PRISON_CELLS);
if (!pool->prison) {
*error = "Error creating pool's bio prison";
@@ -1825,10 +1840,6 @@ static void pool_dtr(struct dm_target *ti)
mutex_unlock(&dm_thin_pool_table.mutex);
}

-struct pool_features {
- unsigned zero_new_blocks:1;
-};
-
static int parse_pool_features(struct dm_arg_set *as, struct pool_features *pf,
struct dm_target *ti)
{
@@ -1837,7 +1848,7 @@ static int parse_pool_features(struct dm_arg_set *as, struct pool_features *pf,
const char *arg_name;

static struct dm_arg _args[] = {
- {0, 1, "Invalid number of pool feature arguments"},
+ {0, 3, "Invalid number of pool feature arguments"},
};

/*
@@ -1857,6 +1868,12 @@ static int parse_pool_features(struct dm_arg_set *as, struct pool_features *pf,
if (!strcasecmp(arg_name, "skip_block_zeroing")) {
pf->zero_new_blocks = 0;
continue;
+ } else if (!strcasecmp(arg_name, "skip_discard")) {
+ pf->discard_enabled = 0;
+ continue;
+ } else if (!strcasecmp(arg_name, "skip_discard_passdown")) {
+ pf->discard_passdown = 0;
+ continue;
}

ti->error = "Unrecognised pool feature requested";
@@ -1874,6 +1891,8 @@ static int parse_pool_features(struct dm_arg_set *as, struct pool_features *pf,
*
* Optional feature arguments are:
* skip_block_zeroing: skips the zeroing of newly-provisioned blocks.
+ * skip_discard: disable discard
+ * skip_discard_passdown: don't pass discards down to the data device
*/
static int pool_ctr(struct dm_target *ti, unsigned argc, char **argv)
{
@@ -1938,8 +1957,7 @@ static int pool_ctr(struct dm_target *ti, unsigned argc, char **argv)
/*
* Set default pool features.
*/
- memset(&pf, 0, sizeof(pf));
- pf.zero_new_blocks = 1;
+ pool_features_init(&pf);

dm_consume_args(&as, 4);
r = parse_pool_features(&as, &pf, ti);
@@ -1964,10 +1982,12 @@ static int pool_ctr(struct dm_target *ti, unsigned argc, char **argv)
pt->metadata_dev = metadata_dev;
pt->data_dev = data_dev;
pt->low_water_blocks = low_water_blocks;
- pt->zero_new_blocks = pf.zero_new_blocks;
+ pt->pf = pf;
ti->num_flush_requests = 1;
- ti->num_discard_requests = 1;
- ti->discards_supported = 1;
+ if (pf.discard_enabled && pf.discard_passdown) {
+ ti->discards_supported = 1;
+ ti->num_discard_requests = 1;
+ }
ti->private = pt;

pt->callbacks.congested_fn = pool_is_congested;
@@ -2303,7 +2323,7 @@ static int pool_message(struct dm_target *ti, unsigned argc, char **argv)
static int pool_status(struct dm_target *ti, status_type_t type,
char *result, unsigned maxlen)
{
- int r;
+ int r, count;
unsigned sz = 0;
uint64_t transaction_id;
dm_block_t nr_free_blocks_data;
@@ -2366,10 +2386,18 @@ static int pool_status(struct dm_target *ti, status_type_t type,
(unsigned long)pool->sectors_per_block,
(unsigned long long)pt->low_water_blocks);

- DMEMIT("%u ", !pool->zero_new_blocks);
+ count = !pool->pf.zero_new_blocks + !pool->pf.discard_enabled + !pool->pf.discard_passdown;
+ DMEMIT("%u ", count);

- if (!pool->zero_new_blocks)
+ if (!pool->pf.zero_new_blocks)
DMEMIT("skip_block_zeroing ");
+
+ if (!pool->pf.discard_enabled)
+ DMEMIT("skip_discard ");
+
+ if (!pool->pf.discard_passdown)
+ DMEMIT("skip_discard_passdown");
+
break;
}

@@ -2407,7 +2435,7 @@ static void set_discard_limits(struct pool *pool, struct queue_limits *limits)
* bios that overlap 2 blocks.
*/
limits->discard_granularity = pool->sectors_per_block << SECTOR_SHIFT;
- limits->discard_zeroes_data = pool->zero_new_blocks;
+ limits->discard_zeroes_data = pool->pf.zero_new_blocks;
}

static void pool_io_hints(struct dm_target *ti, struct queue_limits *limits)
@@ -2417,7 +2445,8 @@ static void pool_io_hints(struct dm_target *ti, struct queue_limits *limits)

blk_limits_io_min(limits, 0);
blk_limits_io_opt(limits, pool->sectors_per_block << SECTOR_SHIFT);
- set_discard_limits(pool, limits);
+ if (pool->pf.discard_enabled)
+ set_discard_limits(pool, limits);
}

static struct target_type pool_target = {
@@ -2466,6 +2495,8 @@ static void thin_dtr(struct dm_target *ti)
* pool_dev: the path to the pool (eg, /dev/mapper/my_pool)
* dev_id: the internal device identifier
* origin_dev: a device external to the pool that should act as the origin
+ *
+ * If the pool has discards disabled, they get disabled for the thin as well.
*/
static int thin_ctr(struct dm_target *ti, unsigned argc, char **argv)
{
@@ -2534,8 +2565,12 @@ static int thin_ctr(struct dm_target *ti, unsigned argc, char **argv)

ti->split_io = tc->pool->sectors_per_block;
ti->num_flush_requests = 1;
- ti->num_discard_requests = 1;
- ti->discards_supported = 1;
+
+ /* In case the pool supports discards, pass them on. */
+ if (tc->pool->pf.discard_enabled) {
+ ti->discards_supported = 1;
+ ti->num_discard_requests = 1;
+ }

dm_put(pool_md);

--
1.7.1

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