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