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author | Mikulas Patocka <mpatocka@redhat.com> | 2014-01-14 01:13:05 +0100 |
---|---|---|
committer | Mike Snitzer <snitzer@redhat.com> | 2014-01-15 05:23:03 +0100 |
commit | 55b082e614e219fb5199a6f93e648ed35d3c96d5 (patch) | |
tree | a2707e62bdd914e9651e78cde6cb55a5f0b88d7f /drivers/md/dm-snap-persistent.c | |
parent | dm snapshot: use dm-bufio (diff) | |
download | linux-55b082e614e219fb5199a6f93e648ed35d3c96d5.tar.xz linux-55b082e614e219fb5199a6f93e648ed35d3c96d5.zip |
dm snapshot: use dm-bufio prefetch
This patch modifies dm-snapshot so that it prefetches the buffers when
loading the exceptions.
The number of buffers read ahead is specified in the DM_PREFETCH_CHUNKS
macro. The current value for DM_PREFETCH_CHUNKS (12) was found to
provide the best performance on a single 15k SCSI spindle. In the
future we may modify this default or make it configurable.
Also, introduce the function dm_bufio_set_minimum_buffers to setup
bufio's number of internal buffers before freeing happens. dm-bufio may
hold more buffers if enough memory is available. There is no guarantee
that the specified number of buffers will be available - if you need a
guarantee, use the argument reserved_buffers for
dm_bufio_client_create.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Diffstat (limited to 'drivers/md/dm-snap-persistent.c')
-rw-r--r-- | drivers/md/dm-snap-persistent.c | 25 |
1 files changed, 24 insertions, 1 deletions
diff --git a/drivers/md/dm-snap-persistent.c b/drivers/md/dm-snap-persistent.c index 169275050c0b..afc3d017de4c 100644 --- a/drivers/md/dm-snap-persistent.c +++ b/drivers/md/dm-snap-persistent.c @@ -18,6 +18,8 @@ #define DM_MSG_PREFIX "persistent snapshot" #define DM_CHUNK_SIZE_DEFAULT_SECTORS 32 /* 16KB */ +#define DM_PREFETCH_CHUNKS 12 + /*----------------------------------------------------------------- * Persistent snapshots, by persistent we mean that the snapshot * will survive a reboot. @@ -497,6 +499,7 @@ static int read_exceptions(struct pstore *ps, { int r, full = 1; struct dm_bufio_client *client; + chunk_t prefetch_area = 0; client = dm_bufio_client_create(dm_snap_cow(ps->store->snap)->bdev, ps->store->chunk_size << SECTOR_SHIFT, @@ -506,13 +509,33 @@ static int read_exceptions(struct pstore *ps, return PTR_ERR(client); /* + * Setup for one current buffer + desired readahead buffers. + */ + dm_bufio_set_minimum_buffers(client, 1 + DM_PREFETCH_CHUNKS); + + /* * Keeping reading chunks and inserting exceptions until * we find a partially full area. */ for (ps->current_area = 0; full; ps->current_area++) { struct dm_buffer *bp; void *area; - chunk_t chunk = area_location(ps, ps->current_area); + chunk_t chunk; + + if (unlikely(prefetch_area < ps->current_area)) + prefetch_area = ps->current_area; + + if (DM_PREFETCH_CHUNKS) do { + chunk_t pf_chunk = area_location(ps, prefetch_area); + if (unlikely(pf_chunk >= dm_bufio_get_device_size(client))) + break; + dm_bufio_prefetch(client, pf_chunk, 1); + prefetch_area++; + if (unlikely(!prefetch_area)) + break; + } while (prefetch_area <= ps->current_area + DM_PREFETCH_CHUNKS); + + chunk = area_location(ps, ps->current_area); area = dm_bufio_read(client, chunk, &bp); if (unlikely(IS_ERR(area))) { |