Calculate byte set size for data sample: Calculate how many unique bytes has been in sample By count all bytes in bucket with count > 0 If byte set low (~25%), data are easily compressible
Signed-off-by: Timofey Titovets <[email protected]> --- fs/btrfs/heuristic.c | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) diff --git a/fs/btrfs/heuristic.c b/fs/btrfs/heuristic.c index 4557ea1db373..953428fde305 100644 --- a/fs/btrfs/heuristic.c +++ b/fs/btrfs/heuristic.c @@ -31,6 +31,7 @@ */ #define MAX_INPUT_PAGES ((BTRFS_MAX_UNCOMPRESSED >> PAGE_SHIFT)+1) #define MAX_SAMPLE_SIZE (MAX_INPUT_PAGES*PAGE_SIZE*READ_SIZE/ITER_SHIFT) +#define BYTE_SET_THRESHOLD 64 struct bucket_item { u32 count; @@ -73,6 +74,27 @@ static struct list_head *heuristic_alloc_workspace(void) return ERR_PTR(-ENOMEM); } +static int byte_set_size(const struct workspace *workspace) +{ + int a = 0; + int byte_set_size = 0; + + for (; a < BYTE_SET_THRESHOLD; a++) { + if (workspace->bucket[a].count > 0) + byte_set_size++; + } + + for (; a < BUCKET_SIZE; a++) { + if (workspace->bucket[a].count > 0) { + byte_set_size++; + if (byte_set_size > BYTE_SET_THRESHOLD) + return byte_set_size; + } + } + + return byte_set_size; +} + static bool sample_zeroed(struct workspace *workspace) { u32 i; @@ -135,6 +157,10 @@ static int heuristic(struct list_head *ws, struct inode *inode, workspace->bucket[byte].count++; } + a = byte_set_size(workspace); + if (a > BYTE_SET_THRESHOLD) + return 2; + return 1; } -- 2.14.1 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
