diff options
| author | Mikulas Patocka | 2009-12-10 23:52:31 +0000 |
|---|---|---|
| committer | Alasdair G Kergon | 2009-12-10 23:52:31 +0000 |
| commit | 3452c2a1eb5b93c1b9fb0d22bd5b07c0cee4dc29 (patch) | |
| tree | 65d4af8d6cf36ac4bcc8c226f8be891740d343ee | |
| parent | 515ad66cc4c82f210d726340349c8f7c1ec6b125 (diff) | |
dm snapshot: avoid allocating exceptions in merge
The snapshot-merge target should not allocate new exceptions because the
intent is to merge all of its exceptions as quickly and safely as
possible.
This patch introduces the snapshot-merge mapping function and updates
__origin_write() so that it doesn't allocate exceptions on any snapshots
that are being merged.
If a write request to a merging snapshot device is to be dispatched
directly to the origin (because the chunk is not remapped or was already
merged), snapshot_merge_map() must make exceptions in other snapshots so
calls do_origin().
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
| -rw-r--r-- | drivers/md/dm-snap.c | 57 |
1 files changed, 56 insertions, 1 deletions
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c index c01e0dafec3c..59d9ef6f5051 100644 --- a/drivers/md/dm-snap.c +++ b/drivers/md/dm-snap.c @@ -1308,6 +1308,54 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio, return r; } +/* + * A snapshot-merge target behaves like a combination of a snapshot + * target and a snapshot-origin target. It only generates new + * exceptions in other snapshots and not in the one that is being + * merged. + * + * For each chunk, if there is an existing exception, it is used to + * redirect I/O to the cow device. Otherwise I/O is sent to the origin, + * which in turn might generate exceptions in other snapshots. + */ +static int snapshot_merge_map(struct dm_target *ti, struct bio *bio, + union map_info *map_context) +{ + struct dm_exception *e; + struct dm_snapshot *s = ti->private; + int r = DM_MAPIO_REMAPPED; + chunk_t chunk; + + chunk = sector_to_chunk(s->store, bio->bi_sector); + + down_read(&s->lock); + + /* Full snapshots are not usable */ + if (!s->valid) { + r = -EIO; + goto out_unlock; + } + + /* If the block is already remapped - use that */ + e = dm_lookup_exception(&s->complete, chunk); + if (e) { + remap_exception(s, e, bio, chunk); + goto out_unlock; + } + + bio->bi_bdev = s->origin->bdev; + + if (bio_rw(bio) == WRITE) { + up_read(&s->lock); + return do_origin(s->origin, bio); + } + +out_unlock: + up_read(&s->lock); + + return r; +} + static int snapshot_end_io(struct dm_target *ti, struct bio *bio, int error, union map_info *map_context) { @@ -1465,6 +1513,13 @@ static int __origin_write(struct list_head *snapshots, sector_t sector, /* Do all the snapshots on this origin */ list_for_each_entry (snap, snapshots, list) { + /* + * Don't make new exceptions in a merging snapshot + * because it has effectively been deleted + */ + if (dm_target_is_snapshot_merge(snap->ti)) + continue; + down_write(&snap->lock); /* Only deal with valid and active snapshots */ @@ -1697,7 +1752,7 @@ static struct target_type merge_target = { .module = THIS_MODULE, .ctr = snapshot_ctr, .dtr = snapshot_dtr, - .map = snapshot_map, + .map = snapshot_merge_map, .end_io = snapshot_end_io, .postsuspend = snapshot_postsuspend, .preresume = snapshot_preresume, |