From 55b082e614e219fb5199a6f93e648ed35d3c96d5 Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Mon, 13 Jan 2014 19:13:05 -0500 Subject: [PATCH] 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-bufio.c | 14 ++++++++++++-- drivers/md/dm-bufio.h | 5 +++++ drivers/md/dm-snap-persistent.c | 25 ++++++++++++++++++++++++- 3 files changed, 41 insertions(+), 3 deletions(-) diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c index d86593721915..9ed42125514b 100644 --- a/drivers/md/dm-bufio.c +++ b/drivers/md/dm-bufio.c @@ -104,6 +104,8 @@ struct dm_bufio_client { struct list_head reserved_buffers; unsigned need_reserved_buffers; + unsigned minimum_buffers; + struct hlist_head *cache_hash; wait_queue_head_t free_buffer_wait; @@ -861,8 +863,8 @@ static void __get_memory_limit(struct dm_bufio_client *c, buffers = dm_bufio_cache_size_per_client >> (c->sectors_per_block_bits + SECTOR_SHIFT); - if (buffers < DM_BUFIO_MIN_BUFFERS) - buffers = DM_BUFIO_MIN_BUFFERS; + if (buffers < c->minimum_buffers) + buffers = c->minimum_buffers; *limit_buffers = buffers; *threshold_buffers = buffers * DM_BUFIO_WRITEBACK_PERCENT / 100; @@ -1372,6 +1374,12 @@ void dm_bufio_forget(struct dm_bufio_client *c, sector_t block) } EXPORT_SYMBOL(dm_bufio_forget); +void dm_bufio_set_minimum_buffers(struct dm_bufio_client *c, unsigned n) +{ + c->minimum_buffers = n; +} +EXPORT_SYMBOL(dm_bufio_set_minimum_buffers); + unsigned dm_bufio_get_block_size(struct dm_bufio_client *c) { return c->block_size; @@ -1568,6 +1576,8 @@ struct dm_bufio_client *dm_bufio_client_create(struct block_device *bdev, unsign INIT_LIST_HEAD(&c->reserved_buffers); c->need_reserved_buffers = reserved_buffers; + c->minimum_buffers = DM_BUFIO_MIN_BUFFERS; + init_waitqueue_head(&c->free_buffer_wait); c->async_write_error = 0; diff --git a/drivers/md/dm-bufio.h b/drivers/md/dm-bufio.h index 3dac37627ba4..c096779a7292 100644 --- a/drivers/md/dm-bufio.h +++ b/drivers/md/dm-bufio.h @@ -115,6 +115,11 @@ void dm_bufio_release_move(struct dm_buffer *b, sector_t new_block); */ void dm_bufio_forget(struct dm_bufio_client *c, sector_t block); +/* + * Set the minimum number of buffers before cleanup happens. + */ +void dm_bufio_set_minimum_buffers(struct dm_bufio_client *c, unsigned n); + unsigned dm_bufio_get_block_size(struct dm_bufio_client *c); sector_t dm_bufio_get_device_size(struct dm_bufio_client *c); sector_t dm_bufio_get_block_number(struct dm_buffer *b); 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))) {