From 55b082e614e219fb5199a6f93e648ed35d3c96d5 Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Mon, 13 Jan 2014 19:13:05 -0500 Subject: 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 Signed-off-by: Mike Snitzer --- drivers/md/dm-snap-persistent.c | 25 ++++++++++++++++++++++++- 1 file changed, 24 insertions(+), 1 deletion(-) (limited to 'drivers/md/dm-snap-persistent.c') 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, @@ -505,6 +508,11 @@ static int read_exceptions(struct pstore *ps, if (IS_ERR(client)) 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. @@ -512,7 +520,22 @@ static int read_exceptions(struct pstore *ps, 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))) { -- cgit v1.2.3