f2fs: compress: don't {,de}compress non-full cluster

f2fs won't compress non-full cluster in tail of file, let's skip
dirtying and rewrite such cluster during f2fs_ioc_{,de}compress_file.

Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Author: chaseyu

fs/f2fs/file.c

@@ -4092,10 +4092,8 @@ static int f2fs_ioc_decompress_file(struct file *filp)
 	last_idx = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
 
 	count = last_idx - page_idx;
-	while (count) {
-		int len = min(cluster_size, count);
-
-		ret = redirty_blocks(inode, page_idx, len);
+	while (count && count >= cluster_size) {
+		ret = redirty_blocks(inode, page_idx, cluster_size);
 		if (ret < 0)
 			break;
 
@@ -4105,8 +4103,8 @@ static int f2fs_ioc_decompress_file(struct file *filp)
 				break;
 		}
 
-		count -= len;
-		page_idx += len;
+		count -= cluster_size;
+		page_idx += cluster_size;
 
 		cond_resched();
 		if (fatal_signal_pending(current)) {
@@ -4172,10 +4170,8 @@ static int f2fs_ioc_compress_file(struct file *filp)
 	last_idx = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
 
 	count = last_idx - page_idx;
-	while (count) {
-		int len = min(cluster_size, count);
-
-		ret = redirty_blocks(inode, page_idx, len);
+	while (count && count >= cluster_size) {
+		ret = redirty_blocks(inode, page_idx, cluster_size);
 		if (ret < 0)
 			break;
 
@@ -4185,8 +4181,8 @@ static int f2fs_ioc_compress_file(struct file *filp)
 				break;
 		}
 
-		count -= len;
-		page_idx += len;
+		count -= cluster_size;
+		page_idx += cluster_size;
 
 		cond_resched();
 		if (fatal_signal_pending(current)) {