[PATCH] f2fs: compress: allow lz4 to compress data partially

[Chao Yu]

For lz4 worst compress case, caller should allocate buffer with size
of LZ4_compressBound(inputsize) for target compressed data storing.

However lz4 supports partial data compression, so we can get rid of
output buffer size limitation now, then we can avoid 2 * 4KB size
intermediate buffer allocation when log_cluster_size is 2, and avoid
unnecessary compressing work of compressor if we can not save at
least 4KB space.

Suggested-by: Daeho Jeong <daehojeong@xxxxxxxxxx>
Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
---
 fs/f2fs/compress.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
index 5e4947250262..23825f559bcf 100644
--- a/fs/f2fs/compress.c
+++ b/fs/f2fs/compress.c
@@ -228,7 +228,12 @@ static int lz4_init_compress_ctx(struct compress_ctx *cc)
 	if (!cc->private)
 		return -ENOMEM;
 
-	cc->clen = LZ4_compressBound(PAGE_SIZE << cc->log_cluster_size);
+	/*
+	 * we do not change cc->clen to LZ4_compressBound(inputsize) to
+	 * adapt worst compress case, because lz4 algorithm supports partial
+	 * compression.
+	 */
+	cc->clen = cc->rlen - PAGE_SIZE - COMPRESS_HEADER_SIZE;
 	return 0;
 }
 
@@ -244,11 +249,9 @@ static int lz4_compress_pages(struct compress_ctx *cc)
 
 	len = LZ4_compress_default(cc->rbuf, cc->cbuf->cdata, cc->rlen,
 						cc->clen, cc->private);
-	if (!len) {
-		printk_ratelimited("%sF2FS-fs (%s): lz4 compress failed\n",
-				KERN_ERR, F2FS_I_SB(cc->inode)->sb->s_id);
-		return -EIO;
-	}
+	if (!len)
+		return -EAGAIN;
+
 	cc->clen = len;
 	return 0;
 }
-- 
2.18.0.rc1