Get small sample from input data
and calculate byte type count for that sample
Signed-off-by: Timofey Titovets <nefelim4ag@xxxxxxxxx>
---
fs/btrfs/compression.c | 24 ++++++++++++++++++++++--
fs/btrfs/compression.h | 11 +++++++++++
2 files changed, 33 insertions(+), 2 deletions(-)
diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 63f54bd2d5bb..1501d4fe90cc 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_ITERATOR_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 d1f4eee2d0af..984943e5e1ae 100644
--- a/fs/btrfs/compression.h
+++ b/fs/btrfs/compression.h
@@ -129,6 +129,17 @@ 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 {
+ u8 padding;
+ u8 symbol;
+ u16 count;
+};
+
+#define BTRFS_HEURISTIC_READ_SIZE 16
+#define BTRFS_HEURISTIC_READS_PER_PAGE 8*PAGE_SIZE/4096
+#define BTRFS_HEURISTIC_ITERATOR_OFFSET PAGE_SIZE/BTRFS_HEURISTIC_READS_PER_PAGE
+#define BTRFS_HEURISTIC_BUCKET_SIZE 256
+
int btrfs_compress_heuristic(struct inode *inode, u64 start, u64 end);
#endif
--
2.13.3
--
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