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Btrfs: heuristic: add detection of repeated data patterns 

Walk over data sample and use memcmp to detect repeated patterns, like
zeros, but a bit more general.

Signed-off-by: Timofey Titovets <nefelim4ag@gmail.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ minor coding style fixes ]
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Timofey Titovets 2017-09-28 17:33:39 +03:00 committed by David Sterba
parent a440d48c7f
commit 1fe4f6fa5a
1 changed files with 14 additions and 1 deletions
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15
fs/btrfs/compression.c
View File

@ -1222,6 +1222,14 @@ int btrfs_decompress_buf2page(const char *buf, unsigned long buf_start,
return 1;
}
static bool sample_repeated_patterns(struct heuristic_ws *ws)
{
const u32 half_of_sample = ws->sample_size / 2;
const u8 *data = ws->sample;
return memcmp(&data[0], &data[half_of_sample], half_of_sample) == 0;
}
static void heuristic_collect_sample(struct inode *inode, u64 start, u64 end,
struct heuristic_ws *ws)
{
@ -1301,6 +1309,11 @@ int btrfs_compress_heuristic(struct inode *inode, u64 start, u64 end)
heuristic_collect_sample(inode, start, end, ws);
if (sample_repeated_patterns(ws)) {
ret = 1;
goto out;
}
memset(ws->bucket, 0, sizeof(*ws->bucket)*BUCKET_SIZE);
for (i = 0; i < ws->sample_size; i++) {
@ -1308,8 +1321,8 @@ int btrfs_compress_heuristic(struct inode *inode, u64 start, u64 end)
ws->bucket[byte].count++;
}
out:
__free_workspace(0, ws_list, true);
return ret;
}