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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: Timofey Titovets <nefelim4ag@gmail.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ minor coding style fixes, comments updated ]
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Timofey Titovets 2017-09-28 17:33:37 +03:00 committed by David Sterba
parent 4e439a0b18
commit 17b5a6c17e
1 changed files with 52 additions and 1 deletions
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53
fs/btrfs/compression.c
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@ -707,8 +707,47 @@ out:
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 {