[PATCH v4 0/3] Btrfs: populate heuristic with detection logic

[PATCH v4 0/3] Btrfs: populate heuristic with detection logic

[Timofey Titovets]

Based on kdave for-next
As heuristic skeleton already merged
Populate heuristic with basic code.

First patch: add simple sampling code
It's get 16 byte samples with 256 bytes shifts
over input data. Collect info about how many
different bytes (symbols) has been found in sample data

Second patch: add code for calculate
how many unique bytes has been
found in sample data
That can fast detect easy compressible data

Third patch: add code for calculate byte core set size
i.e. how many unique bytes use 90% of sample data
That code require that numbers in bucket must be sorted
That can detect easy compressible data with many repeated bytes
That can detect not compressible data with evenly distributed bytes

Changes v1 -> v2:
  - Change input data iterator shift 512 -> 256
  - Replace magic macro numbers with direct values
  - Drop useless symbol population in bucket
    as no one care about where and what symbol stored
    in bucket at now

Changes v2 -> v3 (only update #3 patch):
  - Fix u64 division problem by use u32 for input_size
  - Fix input size calculation start - end -> end - start
  - Add missing sort.h header

Changes v3 -> v4 (only update #1 patch):
  - Change counter type in bucket item u16 -> u32
  - Drop other fields from bucket item for now,
    no one use it

Timofey Titovets (3):
  Btrfs: heuristic add simple sampling logic
  Btrfs: heuristic add byte set calculation
  Btrfs: heuristic add byte core set calculation

 fs/btrfs/compression.c | 109 ++++++++++++++++++++++++++++++++++++++++++++++++-
 fs/btrfs/compression.h |  11 +++++
 2 files changed, 118 insertions(+), 2 deletions(-)

--
2.14.1

[PATCH v4 1/3] Btrfs: heuristic add simple sampling logic

[Timofey Titovets]

Get small sample from input data and calculate
byte type count for that sample into bucket.
Bucket will store info about which bytes
and how many has been detected in sample

Signed-off-by: Timofey Titovets <nefelim4ag@gmail.com>
---
 fs/btrfs/compression.c | 24 ++++++++++++++++++++++--
 fs/btrfs/compression.h |  8 ++++++++
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 883ecc58fd0d..c078c8d8c034 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -1068,15 +1068,35 @@ int btrfs_compress_heuristic(struct inode *inode, u64 start, u64 end)
 	u64 index = start >> PAGE_SHIFT;
 	u64 end_index = end >> PAGE_SHIFT;
 	struct page *page;
-	int ret = 1;
+	struct heuristic_bucket_item *bucket;
+	int a, b, ret;
+	u8 symbol, *input_data;
+
+	ret = 1;
+
+	bucket = kcalloc(BTRFS_HEURISTIC_BUCKET_SIZE,
+		sizeof(struct heuristic_bucket_item), GFP_NOFS);
+
+	if (!bucket)
+		goto out;

 	while (index <= end_index) {
 		page = find_get_page(inode->i_mapping, index);
-		kmap(page);
+		input_data = kmap(page);
+		a = 0;
+		while (a < PAGE_SIZE) {
+			for (b = 0; b < BTRFS_HEURISTIC_READ_SIZE; b++) {
+				symbol = input_data[a+b];
+				bucket[symbol].count++;
+			}
+			a += BTRFS_HEURISTIC_ITER_OFFSET;
+		}
 		kunmap(page);
 		put_page(page);
 		index++;
 	}

+out:
+	kfree(bucket);
 	return ret;
 }
diff --git a/fs/btrfs/compression.h b/fs/btrfs/compression.h
index 3b1b0ac15fdc..e0421705b80b 100644
--- a/fs/btrfs/compression.h
+++ b/fs/btrfs/compression.h
@@ -128,6 +128,14 @@ struct btrfs_compress_op {
 extern const struct btrfs_compress_op btrfs_zlib_compress;
 extern const struct btrfs_compress_op btrfs_lzo_compress;

+struct heuristic_bucket_item {
+	u32 count;
+};
+
+#define BTRFS_HEURISTIC_READ_SIZE 16
+#define BTRFS_HEURISTIC_ITER_OFFSET 256
+#define BTRFS_HEURISTIC_BUCKET_SIZE 256
+
 int btrfs_compress_heuristic(struct inode *inode, u64 start, u64 end);

 #endif
--
2.14.1

[PATCH v4 2/3] Btrfs: heuristic add byte set calculation

[Timofey Titovets]

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 <nefelim4ag@gmail.com>
---
 fs/btrfs/compression.c | 27 +++++++++++++++++++++++++++
 fs/btrfs/compression.h |  1 +
 2 files changed, 28 insertions(+)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index c078c8d8c034..fe26a44bcc9b 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -1048,6 +1048,27 @@ int btrfs_decompress_buf2page(const char *buf, unsigned long buf_start,
 	return 1;
 }

+static inline int byte_set_size(const struct heuristic_bucket_item *bucket)
+{
+	int a = 0;
+	int byte_set_size = 0;
+
+	for (; a < BTRFS_HEURISTIC_BYTE_SET_THRESHOLD; a++) {
+		if (bucket[a].count > 0)
+			byte_set_size++;
+	}
+
+	for (; a < BTRFS_HEURISTIC_BUCKET_SIZE; a++) {
+		if (bucket[a].count > 0) {
+			byte_set_size++;
+			if (byte_set_size > BTRFS_HEURISTIC_BYTE_SET_THRESHOLD)
+				return byte_set_size;
+		}
+	}
+
+	return byte_set_size;
+}
+
 /*
  * Compression heuristic.
  *
@@ -1096,6 +1117,12 @@ int btrfs_compress_heuristic(struct inode *inode, u64 start, u64 end)
 		index++;
 	}

+	a = byte_set_size(bucket);
+	if (a > BTRFS_HEURISTIC_BYTE_SET_THRESHOLD) {
+		ret = 1;
+		goto out;
+	}
+
 out:
 	kfree(bucket);
 	return ret;
diff --git a/fs/btrfs/compression.h b/fs/btrfs/compression.h
index e0421705b80b..07e3d0652e62 100644
--- a/fs/btrfs/compression.h
+++ b/fs/btrfs/compression.h
@@ -135,6 +135,7 @@ struct heuristic_bucket_item {
 #define BTRFS_HEURISTIC_READ_SIZE 16
 #define BTRFS_HEURISTIC_ITER_OFFSET 256
 #define BTRFS_HEURISTIC_BUCKET_SIZE 256
+#define BTRFS_HEURISTIC_BYTE_SET_THRESHOLD 64

 int btrfs_compress_heuristic(struct inode *inode, u64 start, u64 end);

--
2.14.1

[PATCH v4 3/3] Btrfs: heuristic add byte core set calculation

[Timofey Titovets]

Calculate byte core set for data sample:
Sort bucket's numbers in decreasing order
Count how many numbers use 90% of sample
If core set are low (<=25%), data are easily compressible
If core set high (>=80%), data are not compressible

Signed-off-by: Timofey Titovets <nefelim4ag@gmail.com>
---
 fs/btrfs/compression.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++
 fs/btrfs/compression.h |  2 ++
 2 files changed, 60 insertions(+)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index fe26a44bcc9b..8dc92f42f7c2 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -33,6 +33,7 @@
 #include <linux/bit_spinlock.h>
 #include <linux/slab.h>
 #include <linux/sched/mm.h>
+#include <linux/sort.h>
 #include "ctree.h"
 #include "disk-io.h"
 #include "transaction.h"
@@ -1069,6 +1070,42 @@ static inline int byte_set_size(const struct heuristic_bucket_item *bucket)
 	return byte_set_size;
 }

+/* For bucket sorting */
+static inline int heuristic_bucket_compare(const void *lv, const void *rv)
+{
+	struct heuristic_bucket_item *l = (struct heuristic_bucket_item *)(lv);
+	struct heuristic_bucket_item *r = (struct heuristic_bucket_item *)(rv);
+
+	return r->count - l->count;
+}
+
+/*
+ * Byte Core set size
+ * How many bytes use 90% of sample
+ */
+static inline int byte_core_set_size(struct heuristic_bucket_item *bucket,
+				     u32 core_set_threshold)
+{
+	int a = 0;
+	u32 coreset_sum = 0;
+
+	for (; a < BTRFS_HEURISTIC_BYTE_CORE_SET_LOW; a++)
+		coreset_sum += bucket[a].count;
+
+	if (coreset_sum > core_set_threshold)
+		return a;
+
+	for (; a < BTRFS_HEURISTIC_BYTE_CORE_SET_HIGH; a++) {
+		if (bucket[a].count == 0)
+			break;
+		coreset_sum += bucket[a].count;
+		if (coreset_sum > core_set_threshold)
+			break;
+	}
+
+	return a;
+}
+
 /*
  * Compression heuristic.
  *
@@ -1092,6 +1129,8 @@ int btrfs_compress_heuristic(struct inode *inode, u64 start, u64 end)
 	struct heuristic_bucket_item *bucket;
 	int a, b, ret;
 	u8 symbol, *input_data;
+	u32 core_set_threshold;
+	u32 input_size = end - start;

 	ret = 1;

@@ -1123,6 +1162,25 @@ int btrfs_compress_heuristic(struct inode *inode, u64 start, u64 end)
 		goto out;
 	}

+	/* Sort in reverse order */
+	sort(bucket, BTRFS_HEURISTIC_BUCKET_SIZE,
+	     sizeof(struct heuristic_bucket_item), &heuristic_bucket_compare,
+	     NULL);
+
+	core_set_threshold = (input_size*90)/(BTRFS_HEURISTIC_ITER_OFFSET*100);
+	core_set_threshold *= BTRFS_HEURISTIC_READ_SIZE;
+
+	a = byte_core_set_size(bucket, core_set_threshold);
+	if (a <= BTRFS_HEURISTIC_BYTE_CORE_SET_LOW) {
+		ret = 2;
+		goto out;
+	}
+
+	if (a >= BTRFS_HEURISTIC_BYTE_CORE_SET_HIGH) {
+		ret = 0;
+		goto out;
+	}
+
 out:
 	kfree(bucket);
 	return ret;
diff --git a/fs/btrfs/compression.h b/fs/btrfs/compression.h
index 07e3d0652e62..b369a95c1241 100644
--- a/fs/btrfs/compression.h
+++ b/fs/btrfs/compression.h
@@ -136,6 +136,8 @@ struct heuristic_bucket_item {
 #define BTRFS_HEURISTIC_ITER_OFFSET 256
 #define BTRFS_HEURISTIC_BUCKET_SIZE 256
 #define BTRFS_HEURISTIC_BYTE_SET_THRESHOLD 64
+#define BTRFS_HEURISTIC_BYTE_CORE_SET_LOW  BTRFS_HEURISTIC_BYTE_SET_THRESHOLD
+#define BTRFS_HEURISTIC_BYTE_CORE_SET_HIGH 200 // 80%

 int btrfs_compress_heuristic(struct inode *inode, u64 start, u64 end);

--
2.14.1