@@ -9,7 +9,7 @@ btrfs-y += super.o ctree.o extent-tree.o print-tree.o root-tree.o dir-item.o \
export.o tree-log.o free-space-cache.o zlib.o lzo.o \
compression.o delayed-ref.o relocation.o delayed-inode.o scrub.o \
reada.o backref.o ulist.o qgroup.o send.o dev-replace.o raid56.o \
- uuid-tree.o props.o hash.o free-space-tree.o
+ uuid-tree.o props.o hash.o free-space-tree.o heuristic.o log2_lshift16.o
btrfs-$(CONFIG_BTRFS_FS_POSIX_ACL) += acl.o
btrfs-$(CONFIG_BTRFS_FS_CHECK_INTEGRITY) += check-integrity.o
new file mode 100644
@@ -0,0 +1,258 @@
+#include <linux/kernel.h>
+#include <linux/types.h>
+#include <linux/string.h>
+#include <linux/fs.h>
+#include <linux/pagemap.h>
+#include <linux/highmem.h>
+#include <linux/sort.h>
+#include <linux/slab.h>
+
+#include "heuristic.h"
+/* Precalculated log2 realization */
+#include "log2_lshift16.h"
+
+/* For shannon full integer entropy calculation */
+#define BUCKET_SIZE (1 << 8)
+
+struct _backet_item {
+ u8 padding;
+ u8 symbol;
+ u16 count;
+};
+
+
+/* For sorting */
+static int compare(const void *lhs, const void *rhs) {
+ struct _backet_item *l = (struct _backet_item *)(lhs);
+ struct _backet_item *r = (struct _backet_item *)(rhs);
+ return r->count - l->count;
+}
+
+/*
+ * For good compressible data
+ * u8set size over sample
+ * will be small <= 64
+ */
+static u32 _symbset_calc(const struct _backet_item *bucket)
+{
+ u32 a = 0;
+ u32 symbset_size = 0;
+ for (; a < BUCKET_SIZE && symbset_size <= 64; a++) {
+ if (bucket[a].count)
+ symbset_size++;
+ }
+ return symbset_size;
+}
+
+
+/*
+ * Try calculate coreset size
+ * i.e. how many symbols use 90% of input data
+ * < 50 - good compressible data
+ * > 200 - bad compressible data
+ * For right & fast calculation bucket must be reverse sorted
+ */
+static u32 _coreset_calc(const struct _backet_item *bucket,
+ const u32 sum_threshold)
+{
+ u32 a = 0;
+ u32 coreset_sum = 0;
+
+ for (a = 0; a < 201 && bucket[a].count; a++) {
+ coreset_sum += bucket[a].count;
+ if (coreset_sum > sum_threshold)
+ break;
+ }
+
+ return a;
+}
+
+static u64 _entropy_perc(const struct _backet_item *bucket,
+ const u32 sample_size)
+{
+ u64 a, p;
+ u64 entropy_sum = 0;
+ u64 entropy_max = LOG2_RET_SHIFT*8;
+
+ for (a = 0; a < BUCKET_SIZE && bucket[a].count > 0; a++) {
+ p = bucket[a].count;
+ p = p*LOG2_ARG_SHIFT/sample_size;
+ entropy_sum += -p*log2_lshift16(p);
+ }
+
+ entropy_sum = entropy_sum / LOG2_ARG_SHIFT;
+ return entropy_sum*100/entropy_max;
+}
+
+/* Pair distance from random distribution */
+static int _rnd_dist(const struct _backet_item *bucket,
+ const u32 coreset_size, const u8 *sample, u32 sample_size)
+{
+ u64 a, b;
+ u8 pair_a[2], pair_b[2];
+ u64 pairs_count;
+ u64 sum = 0;
+ u64 buf1, buf2;
+ for (a = 0; a < coreset_size-1; a++) {
+ pairs_count = 0;
+ pair_a[0] = bucket[a].symbol;
+ pair_a[1] = bucket[a+1].symbol;
+ pair_b[1] = bucket[a].symbol;
+ pair_b[0] = bucket[a+1].symbol;
+ for (b = 0; b < sample_size-1; b++) {
+ u16 *pair_c = (u16 *) &sample[b];
+ if ( pair_c == (u16 *) pair_a || pair_c == (u16 *) pair_b)
+ pairs_count++;
+ }
+ buf1 = bucket[a].count*bucket[a+1].count;
+ buf1 = buf1*100000/(sample_size*sample_size);
+ buf2 = pairs_count*2*100000;
+ buf2 = pairs_count/sample_size;
+ sum += (buf1 - buf2)*(buf1 - buf2);
+ }
+
+ return sum/2048;
+}
+
+/*
+ * Algorithm description
+ * 1. Get subset of data for fast computation
+ * 2. Scan bucket for symbol set
+ * - symbol set < 64 - data will be easy compressible, return
+ * 3. Try compute coreset size (symbols count that use 90% of input data)
+ * - reverse sort bucket
+ * - sum cells until we reach 90% threshold,
+ * incriment coreset size each time
+ * - coreset_size < 50 - data will be easy compressible, return
+ * coreset_size > 200 - data will be bad compressible, return
+ * in general this looks like data compression ratio 0.2 - 0.8
+ * 4. Compute shannon entropy
+ * - shannon entropy count of bytes and can't count pairs & entropy_calc
+ * so assume:
+ * - usage of entropy can lead to false negative
+ * so for prevent that (in bad) case it's usefull to "count" pairs
+ * - entropy are not to high < 70% easy compressible, return
+ * - entropy are high < 90%, try count pairs,
+ * if there is any noticeable amount, compression are possible, return
+ * - entropy are high > 90%, try count pairs,
+ * if there is noticeable amount, compression are possible, return
+ */
+
+#define READ_SIZE 16
+
+enum compression_advice btrfs_compress_heuristic(struct inode *inode,
+ u64 start, u64 end)
+{
+ enum compression_advice ret = COMPRESS_NONE;
+ u64 bytes_len = end - start;
+ u64 index = start >> PAGE_SHIFT;
+ u64 end_index = end >> PAGE_SHIFT;
+ struct page *page;
+ u8 *input_data;
+ u64 offset_count, shift, sample_size;
+ u64 a, b, c;
+ struct _backet_item bucket[BUCKET_SIZE];
+ u8 *sample;
+
+ /*
+ * In data: 128K 64K 32K 4K
+ * Sample: 4096b 3072b 2048b 1024b
+ * Avoid allocating array bigger then 4kb
+ */
+
+ offset_count = 64 + bytes_len/512;
+
+ if (bytes_len >= 96*1024)
+ offset_count = 256;
+
+ shift = bytes_len/offset_count;
+ sample_size = offset_count*READ_SIZE;
+
+ /*
+ * speedup by copy data to sample array +30%
+ * I think it's because of memcpy speed and
+ * cpu cache hits
+ */
+ sample = kmalloc(sample_size, GFP_NOFS);
+ if (!sample)
+ goto out;
+
+ memset(&bucket, 0, sizeof(bucket));
+
+ /* Preset symbols */
+ for (a = 0; a < BUCKET_SIZE; a++) {
+ bucket[a].symbol = a;
+ }
+
+ /* Read small subset of data 1024b-4096b */
+ a = 0; b = 0; c = 0;
+ while (index <= end_index) {
+ page = find_get_page(inode->i_mapping, index);
+ BUG_ON(!page); /* Pages should be in the extent_io_tree */
+ input_data = kmap(page);
+ c = 0;
+ while (c < c+PAGE_SIZE && a < bytes_len && b < sample_size) {
+ memcpy(&sample[b], &input_data[c], READ_SIZE);
+ c += shift;
+ a += shift;
+ b += READ_SIZE;
+ }
+ kunmap(page);
+ put_page(page);
+ index++;
+ }
+
+ for (a = 0; a < sample_size; a++) {
+ bucket[sample[a]].count++;
+ }
+
+ a = _symbset_calc(bucket);
+ if (a < 64) {
+ ret = COMPRESS_COST_EASY;
+ goto out;
+ }
+
+ /* Sort in reverse order */
+ sort(bucket, BUCKET_SIZE, sizeof(u32), &compare, NULL);
+
+ a = _coreset_calc(bucket, sample_size*90/100);
+
+ if (a < 50) {
+ ret = COMPRESS_COST_EASY;
+ goto out;
+ }
+
+ if (a > 200) {
+ ret = COMPRESS_NONE;
+ goto out;
+ }
+
+ /*
+ * Okay, code fail to fast detect data type
+ * Let's calculate entropy
+ */
+ b = _entropy_perc(bucket, sample_size);
+ if (b < 70) {
+ ret = COMPRESS_COST_MEDIUM;
+ goto out;
+ }
+
+ a = _rnd_dist(bucket, a, sample, sample_size);
+ if (b < 90) {
+ if (a > 0)
+ ret = COMPRESS_COST_MEDIUM;
+ else
+ ret = COMPRESS_NONE;
+ goto out;
+ } else {
+ if (a > 10)
+ ret = COMPRESS_COST_HARD;
+ else
+ ret = COMPRESS_NONE;
+ goto out;
+ }
+
+out:
+ kfree(sample);
+ return ret;
+}
new file mode 100644
@@ -0,0 +1,13 @@
+#include <linux/kernel.h>
+#include <linux/types.h>
+#include <linux/fs.h>
+
+enum compression_advice {
+ COMPRESS_NONE,
+ COMPRESS_COST_EASY,
+ COMPRESS_COST_MEDIUM,
+ COMPRESS_COST_HARD
+};
+
+enum compression_advice btrfs_compress_heuristic(struct inode *inode,
+ u64 start, u64 end);
@@ -60,6 +60,7 @@
#include "props.h"
#include "qgroup.h"
#include "dedupe.h"
+#include "heuristic.h"
struct btrfs_iget_args {
struct btrfs_key *location;
@@ -458,16 +459,16 @@ static noinline void compress_file_range(struct inode *inode,
unsigned long total_compressed = 0;
unsigned long total_in = 0;
int i;
- int will_compress;
+ bool will_compress;
int compress_type = fs_info->compress_type;
- int redirty = 0;
+ bool redirty = false;
inode_should_defrag(BTRFS_I(inode), start, end, end - start + 1,
SZ_16K);
actual_end = min_t(u64, isize, end + 1);
again:
- will_compress = 0;
+ will_compress = false;
nr_pages = (end >> PAGE_SHIFT) - (start >> PAGE_SHIFT) + 1;
BUILD_BUG_ON((BTRFS_MAX_COMPRESSED % PAGE_SIZE) != 0);
nr_pages = min_t(unsigned long, nr_pages,
@@ -510,15 +511,6 @@ static noinline void compress_file_range(struct inode *inode,
*/
if (inode_need_compress(inode)) {
WARN_ON(pages);
- pages = kcalloc(nr_pages, sizeof(struct page *), GFP_NOFS);
- if (!pages) {
- /* just bail out to the uncompressed code */
- goto cont;
- }
-
- if (BTRFS_I(inode)->force_compress)
- compress_type = BTRFS_I(inode)->force_compress;
-
/*
* we need to call clear_page_dirty_for_io on each
* page in the range. Otherwise applications with the file
@@ -529,13 +521,30 @@ static noinline void compress_file_range(struct inode *inode,
* dirty again later on.
*/
extent_range_clear_dirty_for_io(inode, start, end);
- redirty = 1;
+ redirty = true;
+
+ ret = btrfs_compress_heuristic(inode, start, end);
+
+ /* Heuristic say: dont try compress that */
+ if (!ret)
+ goto cont;
+
+ pages = kcalloc(nr_pages, sizeof(struct page *), GFP_NOFS);
+ if (!pages) {
+ /* just bail out to the uncompressed code */
+ goto cont;
+ }
+
+ if (BTRFS_I(inode)->force_compress)
+ compress_type = BTRFS_I(inode)->force_compress;
+
+
ret = btrfs_compress_pages(compress_type,
- inode->i_mapping, start,
- pages,
- &nr_pages,
- &total_in,
- &total_compressed);
+ inode->i_mapping, start,
+ pages,
+ &nr_pages,
+ &total_in,
+ &total_compressed);
if (!ret) {
unsigned long offset = total_compressed &
@@ -552,7 +561,7 @@ static noinline void compress_file_range(struct inode *inode,
PAGE_SIZE - offset);
kunmap_atomic(kaddr);
}
- will_compress = 1;
+ will_compress = true;
}
}
cont:
Add a heuristic computation before compression, for avoiding load resource heavy compression workspace, if data are probably can't be compressed. Signed-off-by: Timofey Titovets <nefelim4ag@gmail.com> --- fs/btrfs/Makefile | 2 +- fs/btrfs/heuristic.c | 258 +++++++++++++++++++++++++++++++++++++++++++++++++++ fs/btrfs/heuristic.h | 13 +++ fs/btrfs/inode.c | 47 ++++++---- 4 files changed, 300 insertions(+), 20 deletions(-) create mode 100644 fs/btrfs/heuristic.c create mode 100644 fs/btrfs/heuristic.h -- 2.13.1 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html