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>
diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index d865937..9ed4212 100644
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -104,6 +104,8 @@
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 @@
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 @@
}
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 @@
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;