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Commit 17b5a6c1 authored by Timofey Titovets's avatar Timofey Titovets Committed by David Sterba
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Btrfs: heuristic: add bucket and sample counters and other defines 



Add basic defines and structures for data sampling.

Added macros:
 - For future sampling algo
 - For bucket size

Heuristic workspace:
 - Add bucket for storing byte type counters
 - Add sample array for storing partial copy of input data range
 - Add counter for store current sample size to workspace

Signed-off-by: default avatarTimofey Titovets <nefelim4ag@gmail.com>
Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
[ minor coding style fixes, comments updated ]
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 4e439a0b

fs/btrfs/compression.c

+52 −1
Original line number Diff line number Diff line
@@ -707,8 +707,47 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio, 
	return ret;

}



/*

 * Heuristic uses systematic sampling to collect data from the input data

 * range, the logic can be tuned by the following constants:

 *

 * @SAMPLING_READ_SIZE - how many bytes will be copied from for each sample

 * @SAMPLING_INTERVAL  - range from which the sampled data can be collected

 */

#define SAMPLING_READ_SIZE	(16)

#define SAMPLING_INTERVAL	(256)



/*

 * For statistical analysis of the input data we consider bytes that form a

 * Galois Field of 256 objects. Each object has an attribute count, ie. how

 * many times the object appeared in the sample.

 */

#define BUCKET_SIZE		(256)



/*

 * The size of the sample is based on a statistical sampling rule of thumb.

 * The common way is to perform sampling tests as long as the number of

 * elements in each cell is at least 5.

 *

 * Instead of 5, we choose 32 to obtain more accurate results.

 * If the data contain the maximum number of symbols, which is 256, we obtain a

 * sample size bound by 8192.

 *

 * For a sample of at most 8KB of data per data range: 16 consecutive bytes

 * from up to 512 locations.

 */

#define MAX_SAMPLE_SIZE		(BTRFS_MAX_UNCOMPRESSED *		\

				 SAMPLING_READ_SIZE / SAMPLING_INTERVAL)



struct bucket_item {

	u32 count;

};



struct heuristic_ws {

	/* Partial copy of input data */

	u8 *sample;

	/* Buckets store counters for each byte value */

	struct bucket_item *bucket;

	struct list_head list;

};
@@ -718,6 +757,8 @@ static void free_heuristic_ws(struct list_head *ws) 


	workspace = list_entry(ws, struct heuristic_ws, list);



	kvfree(workspace->sample);

	kfree(workspace->bucket);

	kfree(workspace);

}
@@ -729,9 +770,19 @@ static struct list_head *alloc_heuristic_ws(void) 
	if (!ws)

		return ERR_PTR(-ENOMEM);



	INIT_LIST_HEAD(&ws->list);

	ws->sample = kvmalloc(MAX_SAMPLE_SIZE, GFP_KERNEL);

	if (!ws->sample)

		goto fail;



	ws->bucket = kcalloc(BUCKET_SIZE, sizeof(*ws->bucket), GFP_KERNEL);

	if (!ws->bucket)

		goto fail;



	INIT_LIST_HEAD(&ws->list);

	return &ws->list;

fail:

	free_heuristic_ws(&ws->list);

	return ERR_PTR(-ENOMEM);

}



struct workspaces_list {