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Commit 1fe4f6fa authored by Timofey Titovets's avatar Timofey Titovets Committed by David Sterba
Browse files

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: default avatarTimofey Titovets <nefelim4ag@gmail.com>
Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
[ minor coding style fixes ]
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent a440d48c

fs/btrfs/compression.c

+14 −1
Original line number Diff line number Diff line
@@ -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;

}