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Add support for DISCARD to ZVOLs.

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DISCARD (REQ_DISCARD, BLKDISCARD) is useful for thin provisioning.
It allows ZVOL clients to discard (unmap, trim) block ranges from
a ZVOL, thus optimizing disk space usage by allowing a ZVOL to
shrink instead of just grow.

We can't use zfs_space() or zfs_freesp() here, since these functions
only work on regular files, not volumes. Fortunately we can use the
low-level function dmu_free_long_range() which does exactly what we
want.

Currently the discard operation is not added to the log. That's not
a big deal since losing discard requests cannot result in data
corruption. It would however result in disk space usage higher than
it should be. Thus adding log support to zvol_discard() is probably
a good idea for a future improvement.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
This commit is contained in:
Etienne Dechamps
2011-09-02 15:23:12 +02:00
committed by Brian Behlendorf
parent cb2d19010d
commit 30930fba21
60 changed files with 273 additions and 0 deletions
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module/zfs/zvol.c
+47
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@@ -574,6 +574,42 @@ zvol_write(void *arg)
blk_end_request(req, -error, size);
}
#ifdef HAVE_BLK_QUEUE_DISCARD
static void
zvol_discard(void *arg)
{
struct request *req = (struct request *)arg;
struct request_queue *q = req->q;
zvol_state_t *zv = q->queuedata;
uint64_t offset = blk_rq_pos(req) << 9;
uint64_t size = blk_rq_bytes(req);
int error;
rl_t *rl;
if (offset + size > zv->zv_volsize) {
blk_end_request(req, -EIO, size);
return;
}
if (size == 0) {
blk_end_request(req, 0, size);
return;
}
rl = zfs_range_lock(&zv->zv_znode, offset, size, RL_WRITER);
error = dmu_free_long_range(zv->zv_objset, ZVOL_OBJ, offset, size);
/*
* TODO: maybe we should add the operation to the log.
*/
zfs_range_unlock(rl);
blk_end_request(req, -error, size);
}
#endif /* HAVE_BLK_QUEUE_DISCARD */
/*
* Common read path running under the zvol taskq context. This function
* is responsible for copying the requested data out of the DMU and in to
@@ -674,6 +710,13 @@ zvol_request(struct request_queue *q)
break;
}
#ifdef HAVE_BLK_QUEUE_DISCARD
if (req->cmd_flags & VDEV_REQ_DISCARD) {
zvol_dispatch(zvol_discard, req);
break;
}
#endif /* HAVE_BLK_QUEUE_DISCARD */
zvol_dispatch(zvol_write, req);
break;
default:
@@ -1193,6 +1236,10 @@ __zvol_create_minor(const char *name)
blk_queue_max_segment_size(zv->zv_queue, UINT_MAX);
blk_queue_physical_block_size(zv->zv_queue, zv->zv_volblocksize);
blk_queue_io_opt(zv->zv_queue, zv->zv_volblocksize);
#ifdef HAVE_BLK_QUEUE_DISCARD
blk_queue_max_discard_sectors(zv->zv_queue, UINT_MAX);
queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, zv->zv_queue);
#endif
#ifdef HAVE_BLK_QUEUE_NONROT
queue_flag_set_unlocked(QUEUE_FLAG_NONROT, zv->zv_queue);
#endif