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Btrfs: heuristic: implement sampling logic 

Copy sample data from the input data range to sample buffer then
calculate byte value count for that sample into bucket.

Signed-off-by: Timofey Titovets <nefelim4ag@gmail.com>
[ minor comment updates ]
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Timofey Titovets 2017-09-28 17:33:38 +03:00 committed by David Sterba
parent 17b5a6c17e
commit a440d48c7f
1 changed files with 62 additions and 9 deletions
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71
fs/btrfs/compression.c
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@ -746,6 +746,7 @@ struct bucket_item {
struct heuristic_ws {
/* Partial copy of input data */
u8 *sample;
u32 sample_size;
/* Buckets store counters for each byte value */
struct bucket_item *bucket;
struct list_head list;
@ -1221,6 +1222,58 @@ int btrfs_decompress_buf2page(const char *buf, unsigned long buf_start,
return 1;
}
static void heuristic_collect_sample(struct inode *inode, u64 start, u64 end,
struct heuristic_ws *ws)
{
struct page *page;
u64 index, index_end;
u32 i, curr_sample_pos;
u8 *in_data;
/*
* Compression handles the input data by chunks of 128KiB
* (defined by BTRFS_MAX_UNCOMPRESSED)
*
* We do the same for the heuristic and loop over the whole range.
*
* MAX_SAMPLE_SIZE - calculated under assumption that heuristic will
* process no more than BTRFS_MAX_UNCOMPRESSED at a time.
*/
if (end - start > BTRFS_MAX_UNCOMPRESSED)
end = start + BTRFS_MAX_UNCOMPRESSED;
index = start >> PAGE_SHIFT;
index_end = end >> PAGE_SHIFT;
/* Don't miss unaligned end */
if (!IS_ALIGNED(end, PAGE_SIZE))
index_end++;
curr_sample_pos = 0;
while (index < index_end) {
page = find_get_page(inode->i_mapping, index);
in_data = kmap(page);
/* Handle case where the start is not aligned to PAGE_SIZE */
i = start % PAGE_SIZE;
while (i < PAGE_SIZE - SAMPLING_READ_SIZE) {
/* Don't sample any garbage from the last page */
if (start > end - SAMPLING_READ_SIZE)
break;
memcpy(&ws->sample[curr_sample_pos], &in_data[i],
SAMPLING_READ_SIZE);
i += SAMPLING_INTERVAL;
start += SAMPLING_INTERVAL;
curr_sample_pos += SAMPLING_READ_SIZE;
}
kunmap(page);
put_page(page);
index++;
}
ws->sample_size = curr_sample_pos;
}
/*
* Compression heuristic.
*
@ -1240,19 +1293,19 @@ int btrfs_compress_heuristic(struct inode *inode, u64 start, u64 end)
{
struct list_head *ws_list = __find_workspace(0, true);
struct heuristic_ws *ws;
u64 index = start >> PAGE_SHIFT;
u64 end_index = end >> PAGE_SHIFT;
struct page *page;
u32 i;
u8 byte;
int ret = 1;
ws = list_entry(ws_list, struct heuristic_ws, list);
while (index <= end_index) {
page = find_get_page(inode->i_mapping, index);
kmap(page);
kunmap(page);
put_page(page);
index++;
heuristic_collect_sample(inode, start, end, ws);
memset(ws->bucket, 0, sizeof(*ws->bucket)*BUCKET_SIZE);
for (i = 0; i < ws->sample_size; i++) {
byte = ws->sample[i];
ws->bucket[byte].count++;
}
__free_workspace(0, ws_list, true);