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 <nefelim...@gmail.com>
---
fs/btrfs/heuristic.c | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/fs/btrfs/heuristic.c b/fs/btrfs/heuristic.c
index 8df56ea93064..4815d1becf7e 100644
--- a/fs/btrfs/heuristic.c
+++ b/fs/btrfs/heuristic.c
@@ -24,6 +24,7 @@
#define ITER_SHIFT 256
#define BUCKET_SIZE 256
#define MAX_SAMPLE_SIZE (BTRFS_MAX_UNCOMPRESSED*READ_SIZE/ITER_SHIFT)
+#define BYTE_SET_THRESHOLD 64
struct bucket_item {
u32 count;
@@ -66,6 +67,27 @@ static struct list_head *heuristic_alloc_workspace(void)
return ERR_PTR(-ENOMEM);
}
+static u32 byte_set_size(const struct workspace *ws)
+{
+ u32 a = 0;
+ u32 byte_set_size = 0;
+
+ for (; a < BYTE_SET_THRESHOLD; a++) {
+ if (ws->bucket[a].count > 0)
+ byte_set_size++;
+ }
+
+ for (; a < BUCKET_SIZE; a++) {
+ if (ws->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_repeated_patterns(struct workspace *ws)
{
u32 i = 0;
@@ -141,6 +163,10 @@ 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
--
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