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dm snapshot: queue writes to chunks being merged

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While a set of chunks is being merged, any overlapping writes need to be
queued.

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>
This commit is contained in:
Mikulas Patocka 2009-12-10 23:52:33 +00:00 committed by Alasdair G Kergon
parent 1e03f97e43
commit 9fe8625488
1 changed files with 78 additions and 13 deletions
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91
drivers/md/dm-snap.c
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@ -109,6 +109,16 @@ struct dm_snapshot {
/* Wait for events based on state_bits */
unsigned long state_bits;
/* Range of chunks currently being merged. */
chunk_t first_merging_chunk;
int num_merging_chunks;
/*
* Incoming bios that overlap with chunks being merged must wait
* for them to be committed.
*/
struct bio_list bios_queued_during_merge;
};
/*
@ -747,6 +757,14 @@ static void merge_shutdown(struct dm_snapshot *s)
wake_up_bit(&s->state_bits, RUNNING_MERGE);
}
static struct bio *__release_queued_bios_after_merge(struct dm_snapshot *s)
{
s->first_merging_chunk = 0;
s->num_merging_chunks = 0;
return bio_list_get(&s->bios_queued_during_merge);
}
/*
* Remove one chunk from the index of completed exceptions.
*/
@ -755,8 +773,6 @@ static int __remove_single_exception_chunk(struct dm_snapshot *s,
{
struct dm_exception *e;
/* FIXME: interlock writes to this chunk */
e = dm_lookup_exception(&s->complete, old_chunk);
if (!e) {
DMERR("Corruption detected: exception for block %llu is "
@ -801,14 +817,32 @@ static int __remove_single_exception_chunk(struct dm_snapshot *s,
return 0;
}
static int remove_single_exception_chunk(struct dm_snapshot *s,
chunk_t old_chunk)
static void flush_bios(struct bio *bio);
static int remove_single_exception_chunk(struct dm_snapshot *s)
{
int r = 0;
struct bio *b = NULL;
int r;
chunk_t old_chunk = s->first_merging_chunk + s->num_merging_chunks - 1;
down_write(&s->lock);
r = __remove_single_exception_chunk(s, old_chunk);
/*
* Process chunks (and associated exceptions) in reverse order
* so that dm_consecutive_chunk_count_dec() accounting works.
*/
do {
r = __remove_single_exception_chunk(s, old_chunk);
if (r)
goto out;
} while (old_chunk-- > s->first_merging_chunk);
b = __release_queued_bios_after_merge(s);
out:
up_write(&s->lock);
if (b)
flush_bios(b);
return r;
}
@ -844,9 +878,6 @@ static void snapshot_merge_next_chunks(struct dm_snapshot *s)
/* TODO: use larger I/O size once we verify that kcopyd handles it */
if (remove_single_exception_chunk(s, old_chunk) < 0)
goto shut;
dest.bdev = s->origin->bdev;
dest.sector = chunk_to_sector(s->store, old_chunk);
dest.count = min((sector_t)s->store->chunk_size,
@ -856,6 +887,13 @@ static void snapshot_merge_next_chunks(struct dm_snapshot *s)
src.sector = chunk_to_sector(s->store, new_chunk);
src.count = dest.count;
down_write(&s->lock);
s->first_merging_chunk = old_chunk;
s->num_merging_chunks = 1;
up_write(&s->lock);
/* !!! FIXME: wait until writes to this chunk drain */
dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, merge_callback, s);
return;
@ -863,9 +901,12 @@ static void snapshot_merge_next_chunks(struct dm_snapshot *s)
merge_shutdown(s);
}
static void error_bios(struct bio *bio);
static void merge_callback(int read_err, unsigned long write_err, void *context)
{
struct dm_snapshot *s = context;
struct bio *b = NULL;
if (read_err || write_err) {
if (read_err)
@ -875,16 +916,25 @@ static void merge_callback(int read_err, unsigned long write_err, void *context)
goto shut;
}
if (s->store->type->commit_merge(s->store, 1) < 0) {
if (s->store->type->commit_merge(s->store,
s->num_merging_chunks) < 0) {
DMERR("Write error in exception store: shutting down merge");
goto shut;
}
if (remove_single_exception_chunk(s) < 0)
goto shut;
snapshot_merge_next_chunks(s);
return;
shut:
down_write(&s->lock);
b = __release_queued_bios_after_merge(s);
up_write(&s->lock);
error_bios(b);
merge_shutdown(s);
}
@ -983,6 +1033,9 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
INIT_LIST_HEAD(&s->list);
spin_lock_init(&s->pe_lock);
s->state_bits = 0;
s->first_merging_chunk = 0;
s->num_merging_chunks = 0;
bio_list_init(&s->bios_queued_during_merge);
/* Allocate hash table for COW data */
if (init_hash_tables(s)) {
@ -1539,6 +1592,8 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio,
* 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.
* If merging is currently taking place on the chunk in question, the
* I/O is deferred by adding it to s->bios_queued_during_merge.
*/
static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,
union map_info *map_context)
@ -1559,7 +1614,7 @@ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,
chunk = sector_to_chunk(s->store, bio->bi_sector);
down_read(&s->lock);
down_write(&s->lock);
/* Full snapshots are not usable */
if (!s->valid) {
@ -1570,6 +1625,16 @@ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,
/* If the block is already remapped - use that */
e = dm_lookup_exception(&s->complete, chunk);
if (e) {
/* Queue writes overlapping with chunks being merged */
if (bio_rw(bio) == WRITE &&
chunk >= s->first_merging_chunk &&
chunk < (s->first_merging_chunk +
s->num_merging_chunks)) {
bio->bi_bdev = s->origin->bdev;
bio_list_add(&s->bios_queued_during_merge, bio);
r = DM_MAPIO_SUBMITTED;
goto out_unlock;
}
remap_exception(s, e, bio, chunk);
goto out_unlock;
}
@ -1577,12 +1642,12 @@ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,
bio->bi_bdev = s->origin->bdev;
if (bio_rw(bio) == WRITE) {
up_read(&s->lock);
up_write(&s->lock);
return do_origin(s->origin, bio);
}
out_unlock:
up_read(&s->lock);
up_write(&s->lock);
return r;
}