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dm snapshot: use dm-bufio prefetch

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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>
This commit is contained in:
Mikulas Patocka
2014-01-13 19:13:05 -05:00
committed by Mike Snitzer
parent 55494bf294
commit 55b082e614
3 changed files with 41 additions and 3 deletions
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5
drivers/md/dm-bufio.h
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@@ -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);