[PATCH v2] f2fs: compress: let lz4 compressor handle output buffer budget properly

[Chao Yu]

Commonly, in order to handle lz4 worst compress case, caller should
allocate buffer with size of LZ4_compressBound(inputsize) for target
compressed data storing, however in this case, if caller didn't
allocate enough space, lz4 compressor still can handle output buffer
budget properly, and end up compressing when left space in output
buffer is not enough.

So we don't have to allocate buffer with size for worst case, 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>
---
v2:
- update commit title/message suggested by Gao Xiang
 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..c0880c3e4b6e 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 compressor can handle
+	 * output budget properly.
+	 */
+	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