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dm snapshot: trigger exceptions in remaining snapshots during merge

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When there is one merging snapshot and other non-merging snapshots,
snapshot_merge_process() must make exceptions in the non-merging
snapshots.

Use a sequence count to resolve the race between I/O to chunks that are
about to be merged.  The count increases each time an exception
reallocation finishes.  Use wait_event() to wait until the count
changes.

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 23:52:34 +00:00 committed by Alasdair G Kergon
parent 17aa03326d
commit 73dfd078cf
1 changed files with 83 additions and 0 deletions
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83
drivers/md/dm-snap.c
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@ -270,6 +270,10 @@ struct origin {
static struct list_head *_origins;
static struct rw_semaphore _origins_lock;
static DECLARE_WAIT_QUEUE_HEAD(_pending_exceptions_done);
static DEFINE_SPINLOCK(_pending_exceptions_done_spinlock);
static uint64_t _pending_exceptions_done_count;
static int init_origin_hash(void)
{
int i;
@ -847,14 +851,38 @@ out:
return r;
}
static int origin_write_extent(struct dm_snapshot *merging_snap,
sector_t sector, unsigned chunk_size);
static void merge_callback(int read_err, unsigned long write_err,
void *context);
static uint64_t read_pending_exceptions_done_count(void)
{
uint64_t pending_exceptions_done;
spin_lock(&_pending_exceptions_done_spinlock);
pending_exceptions_done = _pending_exceptions_done_count;
spin_unlock(&_pending_exceptions_done_spinlock);
return pending_exceptions_done;
}
static void increment_pending_exceptions_done_count(void)
{
spin_lock(&_pending_exceptions_done_spinlock);
_pending_exceptions_done_count++;
spin_unlock(&_pending_exceptions_done_spinlock);
wake_up_all(&_pending_exceptions_done);
}
static void snapshot_merge_next_chunks(struct dm_snapshot *s)
{
int r;
chunk_t old_chunk, new_chunk;
struct dm_io_region src, dest;
uint64_t previous_count;
BUG_ON(!test_bit(RUNNING_MERGE, &s->state_bits));
if (unlikely(test_bit(SHUTDOWN_MERGE, &s->state_bits)))
@ -887,6 +915,24 @@ static void snapshot_merge_next_chunks(struct dm_snapshot *s)
src.sector = chunk_to_sector(s->store, new_chunk);
src.count = dest.count;
/*
* Reallocate any exceptions needed in other snapshots then
* wait for the pending exceptions to complete.
* Each time any pending exception (globally on the system)
* completes we are woken and repeat the process to find out
* if we can proceed. While this may not seem a particularly
* efficient algorithm, it is not expected to have any
* significant impact on performance.
*/
previous_count = read_pending_exceptions_done_count();
while (origin_write_extent(s, dest.sector, s->store->chunk_size)) {
wait_event(_pending_exceptions_done,
(read_pending_exceptions_done_count() !=
previous_count));
/* Retry after the wait, until all exceptions are done. */
previous_count = read_pending_exceptions_done_count();
}
down_write(&s->lock);
s->first_merging_chunk = old_chunk;
s->num_merging_chunks = 1;
@ -1372,6 +1418,8 @@ static void pending_complete(struct dm_snap_pending_exception *pe, int success)
origin_bios = bio_list_get(&pe->origin_bios);
free_pending_exception(pe);
increment_pending_exceptions_done_count();
up_write(&s->lock);
/* Submit any pending write bios */
@ -1962,6 +2010,41 @@ static int do_origin(struct dm_dev *origin, struct bio *bio)
return r;
}
/*
* Trigger exceptions in all non-merging snapshots.
*
* The chunk size of the merging snapshot may be larger than the chunk
* size of some other snapshot so we may need to reallocate multiple
* chunks in other snapshots.
*
* We scan all the overlapping exceptions in the other snapshots.
* Returns 1 if anything was reallocated and must be waited for,
* otherwise returns 0.
*
* size must be a multiple of merging_snap's chunk_size.
*/
static int origin_write_extent(struct dm_snapshot *merging_snap,
sector_t sector, unsigned size)
{
int must_wait = 0;
sector_t n;
struct origin *o;
/*
* The origin's __minimum_chunk_size() got stored in split_io
* by snapshot_merge_resume().
*/
down_read(&_origins_lock);
o = __lookup_origin(merging_snap->origin->bdev);
for (n = 0; n < size; n += merging_snap->ti->split_io)
if (__origin_write(&o->snapshots, sector + n, NULL) ==
DM_MAPIO_SUBMITTED)
must_wait = 1;
up_read(&_origins_lock);
return must_wait;
}
/*
* Origin: maps a linear range of a device, with hooks for snapshotting.
*/