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dm snapshot: merge consecutive chunks together 

s->store->type->prepare_merge returns the number of chunks that can be
copied linearly working backwards from the returned chunk number.

For example, if it returns 3 chunks with old_chunk == 10 and new_chunk
== 20, then chunk 20 can be copied to 10, chunk 19 to 9 and 18 to 8.

Until now kcopyd only copied one chunk at a time.  This patch now copies
the full set at once.

Consequently, snapshot_merge_process() needs to delay the merging of all
chunks if any have writes in progress, not just the first chunk in the
region that is to be merged.

snapshot-merge's performance is now comparable to the original
snapshot-origin target.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This commit is contained in:
Mike Snitzer 2009-12-10 23:52:34 +00:00 committed by Alasdair G Kergon
parent 73dfd078cf
commit 8a2d528620
1 changed files with 21 additions and 10 deletions
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31
drivers/md/dm-snap.c
View File

@ -879,9 +879,10 @@ static void increment_pending_exceptions_done_count(void)
static void snapshot_merge_next_chunks(struct dm_snapshot *s)
{
int r;
int i, linear_chunks;
chunk_t old_chunk, new_chunk;
struct dm_io_region src, dest;
sector_t io_size;
uint64_t previous_count;
BUG_ON(!test_bit(RUNNING_MERGE, &s->state_bits));
@ -896,20 +897,28 @@ static void snapshot_merge_next_chunks(struct dm_snapshot *s)
goto shut;
}
r = s->store->type->prepare_merge(s->store, &old_chunk, &new_chunk);
if (r <= 0) {
if (r < 0)
linear_chunks = s->store->type->prepare_merge(s->store, &old_chunk,
&new_chunk);
if (linear_chunks <= 0) {
if (linear_chunks < 0)
DMERR("Read error in exception store: "
"shutting down merge");
goto shut;
}
/* TODO: use larger I/O size once we verify that kcopyd handles it */
/* Adjust old_chunk and new_chunk to reflect start of linear region */
old_chunk = old_chunk + 1 - linear_chunks;
new_chunk = new_chunk + 1 - linear_chunks;
/*
* Use one (potentially large) I/O to copy all 'linear_chunks'
* from the exception store to the origin
*/
io_size = linear_chunks * s->store->chunk_size;
dest.bdev = s->origin->bdev;
dest.sector = chunk_to_sector(s->store, old_chunk);
dest.count = min((sector_t)s->store->chunk_size,
get_dev_size(dest.bdev) - dest.sector);
dest.count = min(io_size, get_dev_size(dest.bdev) - dest.sector);
src.bdev = s->cow->bdev;
src.sector = chunk_to_sector(s->store, new_chunk);
@ -925,7 +934,7 @@ static void snapshot_merge_next_chunks(struct dm_snapshot *s)
* significant impact on performance.
*/
previous_count = read_pending_exceptions_done_count();
while (origin_write_extent(s, dest.sector, s->store->chunk_size)) {
while (origin_write_extent(s, dest.sector, io_size)) {
wait_event(_pending_exceptions_done,
(read_pending_exceptions_done_count() !=
previous_count));
@ -935,10 +944,12 @@ static void snapshot_merge_next_chunks(struct dm_snapshot *s)
down_write(&s->lock);
s->first_merging_chunk = old_chunk;
s->num_merging_chunks = 1;
s->num_merging_chunks = linear_chunks;
up_write(&s->lock);
__check_for_conflicting_io(s, old_chunk);
/* Wait until writes to all 'linear_chunks' drain */
for (i = 0; i < linear_chunks; i++)
__check_for_conflicting_io(s, old_chunk + i);
dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, merge_callback, s);
return;