diff options
Diffstat (limited to 'fs/btrfs/compression.c')
| -rw-r--r-- | fs/btrfs/compression.c | 45 |
1 files changed, 45 insertions, 0 deletions
diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c index 0d445c815ca2..e949f078a81b 100644 --- a/fs/btrfs/compression.c +++ b/fs/btrfs/compression.c @@ -1222,6 +1222,45 @@ int btrfs_decompress_buf2page(const char *buf, unsigned long buf_start, return 1; } +/* + * Count byte values in buckets. + * This heuristic can detect textual data (configs, xml, json, html, etc). + * Because in most text-like data byte set is restricted to limited number of + * possible characters, and that restriction in most cases makes data easy to + * compress. + * + * @BYTE_SET_THRESHOLD - consider all data within this byte set size: + * less - compressible + * more - need additional analysis + */ +#define BYTE_SET_THRESHOLD (64) + +static u32 byte_set_size(const struct heuristic_ws *ws) +{ + u32 i; + u32 byte_set_size = 0; + + for (i = 0; i < BYTE_SET_THRESHOLD; i++) { + if (ws->bucket[i].count > 0) + byte_set_size++; + } + + /* + * Continue collecting count of byte values in buckets. If the byte + * set size is bigger then the threshold, it's pointless to continue, + * the detection technique would fail for this type of data. + */ + for (; i < BUCKET_SIZE; i++) { + if (ws->bucket[i].count > 0) { + byte_set_size++; + if (byte_set_size > BYTE_SET_THRESHOLD) + return byte_set_size; + } + } + + return byte_set_size; +} + static bool sample_repeated_patterns(struct heuristic_ws *ws) { const u32 half_of_sample = ws->sample_size / 2; @@ -1321,6 +1360,12 @@ int btrfs_compress_heuristic(struct inode *inode, u64 start, u64 end) ws->bucket[byte].count++; } + i = byte_set_size(ws); + if (i < BYTE_SET_THRESHOLD) { + ret = 2; + goto out; + } + out: __free_workspace(0, ws_list, true); return ret; |