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authorMikulas Patocka <mpatocka@redhat.com>2011-08-02 12:32:04 +0100
committerAlasdair G Kergon <agk@redhat.com>2011-08-02 12:32:04 +0100
commita6e50b409d3f9e0833e69c3c9cca822e8fa4adbb (patch)
tree82ca807c21156437270e6a1ed255b18ccf8b3672 /drivers/md/dm-snap.c
parentd5b9dd04bd74b774b8e8d93ced7a0d15ad403fa9 (diff)
dm snapshot: skip reading origin when overwriting complete chunk
If we write a full chunk in the snapshot, skip reading the origin device because the whole chunk will be overwritten anyway. This patch changes the snapshot write logic when a full chunk is written. In this case: 1. allocate the exception 2. dispatch the bio (but don't report the bio completion to device mapper) 3. write the exception record 4. report bio completed Callbacks must be done through the kcopyd thread, because callbacks must not race with each other. So we create two new functions: dm_kcopyd_prepare_callback: allocate a job structure and prepare the callback. (This function must not be called from interrupt context.) dm_kcopyd_do_callback: submit callback. (This function may be called from interrupt context.) Performance test (on snapshots with 4k chunk size): without the patch: non-direct-io sequential write (dd): 17.7MB/s direct-io sequential write (dd): 20.9MB/s non-direct-io random write (mkfs.ext2): 0.44s with the patch: non-direct-io sequential write (dd): 26.5MB/s direct-io sequential write (dd): 33.2MB/s non-direct-io random write (mkfs.ext2): 0.27s Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Diffstat (limited to 'drivers/md/dm-snap.c')
-rw-r--r--drivers/md/dm-snap.c60
1 files changed, 57 insertions, 3 deletions
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 94dee05dd28e..6f758870fc19 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -170,6 +170,13 @@ struct dm_snap_pending_exception {
* kcopyd.
*/
int started;
+
+ /*
+ * For writing a complete chunk, bypassing the copy.
+ */
+ struct bio *full_bio;
+ bio_end_io_t *full_bio_end_io;
+ void *full_bio_private;
};
/*
@@ -1369,6 +1376,7 @@ static void pending_complete(struct dm_snap_pending_exception *pe, int success)
struct dm_snapshot *s = pe->snap;
struct bio *origin_bios = NULL;
struct bio *snapshot_bios = NULL;
+ struct bio *full_bio = NULL;
int error = 0;
if (!success) {
@@ -1408,6 +1416,11 @@ out:
dm_remove_exception(&pe->e);
snapshot_bios = bio_list_get(&pe->snapshot_bios);
origin_bios = bio_list_get(&pe->origin_bios);
+ full_bio = pe->full_bio;
+ if (full_bio) {
+ full_bio->bi_end_io = pe->full_bio_end_io;
+ full_bio->bi_private = pe->full_bio_private;
+ }
free_pending_exception(pe);
increment_pending_exceptions_done_count();
@@ -1415,10 +1428,15 @@ out:
up_write(&s->lock);
/* Submit any pending write bios */
- if (error)
+ if (error) {
+ if (full_bio)
+ bio_io_error(full_bio);
error_bios(snapshot_bios);
- else
+ } else {
+ if (full_bio)
+ bio_endio(full_bio, 0);
flush_bios(snapshot_bios);
+ }
retry_origin_bios(s, origin_bios);
}
@@ -1472,6 +1490,32 @@ static void start_copy(struct dm_snap_pending_exception *pe)
dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, copy_callback, pe);
}
+static void full_bio_end_io(struct bio *bio, int error)
+{
+ void *callback_data = bio->bi_private;
+
+ dm_kcopyd_do_callback(callback_data, 0, error ? 1 : 0);
+}
+
+static void start_full_bio(struct dm_snap_pending_exception *pe,
+ struct bio *bio)
+{
+ struct dm_snapshot *s = pe->snap;
+ void *callback_data;
+
+ pe->full_bio = bio;
+ pe->full_bio_end_io = bio->bi_end_io;
+ pe->full_bio_private = bio->bi_private;
+
+ callback_data = dm_kcopyd_prepare_callback(s->kcopyd_client,
+ copy_callback, pe);
+
+ bio->bi_end_io = full_bio_end_io;
+ bio->bi_private = callback_data;
+
+ generic_make_request(bio);
+}
+
static struct dm_snap_pending_exception *
__lookup_pending_exception(struct dm_snapshot *s, chunk_t chunk)
{
@@ -1507,6 +1551,7 @@ __find_pending_exception(struct dm_snapshot *s,
bio_list_init(&pe->origin_bios);
bio_list_init(&pe->snapshot_bios);
pe->started = 0;
+ pe->full_bio = NULL;
if (s->store->type->prepare_exception(s->store, &pe->e)) {
free_pending_exception(pe);
@@ -1600,10 +1645,19 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio,
}
remap_exception(s, &pe->e, bio, chunk);
- bio_list_add(&pe->snapshot_bios, bio);
r = DM_MAPIO_SUBMITTED;
+ if (!pe->started &&
+ bio->bi_size == (s->store->chunk_size << SECTOR_SHIFT)) {
+ pe->started = 1;
+ up_write(&s->lock);
+ start_full_bio(pe, bio);
+ goto out;
+ }
+
+ bio_list_add(&pe->snapshot_bios, bio);
+
if (!pe->started) {
/* this is protected by snap->lock */
pe->started = 1;