f2fs: clean up i_compress_flag and i_compress_level usage

.i_compress_level was introduced by commit 3fde13f8 ("f2fs: compress:
support compress level"), but never be used.

This patch updates as below:
- load high 8-bits of on-disk .i_compress_flag to in-memory .i_compress_level
- load low 8-bits of on-disk .i_compress_flag to in-memory .i_compress_flag
- change type of in-memory .i_compress_flag from unsigned short to unsigned
char.

w/ above changes, we can avoid unneeded bit shift whenever during
.init_compress_ctx(), and shrink size of struct f2fs_inode_info.
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/compress.c

@@ -241,7 +241,7 @@ static int lz4_init_compress_ctx(struct compress_ctx *cc)
 	unsigned int size = LZ4_MEM_COMPRESS;
 
 #ifdef CONFIG_F2FS_FS_LZ4HC
-	if (F2FS_I(cc->inode)->i_compress_flag >> COMPRESS_LEVEL_OFFSET)
+	if (F2FS_I(cc->inode)->i_compress_level)
 		size = LZ4HC_MEM_COMPRESS;
 #endif
 
@@ -267,8 +267,7 @@ static void lz4_destroy_compress_ctx(struct compress_ctx *cc)
 #ifdef CONFIG_F2FS_FS_LZ4HC
 static int lz4hc_compress_pages(struct compress_ctx *cc)
 {
-	unsigned char level = F2FS_I(cc->inode)->i_compress_flag >>
-						COMPRESS_LEVEL_OFFSET;
+	unsigned char level = F2FS_I(cc->inode)->i_compress_level;
 	int len;
 
 	if (level)
@@ -340,8 +339,7 @@ static int zstd_init_compress_ctx(struct compress_ctx *cc)
 	zstd_cstream *stream;
 	void *workspace;
 	unsigned int workspace_size;
-	unsigned char level = F2FS_I(cc->inode)->i_compress_flag >>
-						COMPRESS_LEVEL_OFFSET;
+	unsigned char level = F2FS_I(cc->inode)->i_compress_level;
 
 	if (!level)
 		level = F2FS_ZSTD_DEFAULT_CLEVEL;

fs/f2fs/f2fs.h

@@ -869,7 +869,7 @@ struct f2fs_inode_info {
 	unsigned char i_compress_algorithm;	/* algorithm type */
 	unsigned char i_log_cluster_size;	/* log of cluster size */
 	unsigned char i_compress_level;		/* compress level (lz4hc,zstd) */
-	unsigned short i_compress_flag;		/* compress flag */
+	unsigned char i_compress_flag;		/* compress flag */
 	unsigned int i_cluster_size;		/* cluster size */
 
 	unsigned int atomic_write_cnt;
@@ -4358,9 +4358,8 @@ static inline int set_compress_context(struct inode *inode)
 	if ((F2FS_I(inode)->i_compress_algorithm == COMPRESS_LZ4 ||
 		F2FS_I(inode)->i_compress_algorithm == COMPRESS_ZSTD) &&
 			F2FS_OPTION(sbi).compress_level)
-		F2FS_I(inode)->i_compress_flag |=
-				F2FS_OPTION(sbi).compress_level <<
-				COMPRESS_LEVEL_OFFSET;
+		F2FS_I(inode)->i_compress_level =
+				F2FS_OPTION(sbi).compress_level;
 	F2FS_I(inode)->i_flags |= F2FS_COMPR_FL;
 	set_inode_flag(inode, FI_COMPRESSED_FILE);
 	stat_inc_compr_inode(inode);

fs/f2fs/inode.c

@@ -460,11 +460,17 @@ static int do_read_inode(struct inode *inode)
 					(fi->i_flags & F2FS_COMPR_FL)) {
 		if (F2FS_FITS_IN_INODE(ri, fi->i_extra_isize,
 					i_log_cluster_size)) {
+			unsigned short compress_flag;
+
 			atomic_set(&fi->i_compr_blocks,
 					le64_to_cpu(ri->i_compr_blocks));
 			fi->i_compress_algorithm = ri->i_compress_algorithm;
 			fi->i_log_cluster_size = ri->i_log_cluster_size;
-			fi->i_compress_flag = le16_to_cpu(ri->i_compress_flag);
+			compress_flag = le16_to_cpu(ri->i_compress_flag);
+			fi->i_compress_level = compress_flag >>
+						COMPRESS_LEVEL_OFFSET;
+			fi->i_compress_flag = compress_flag &
+					(BIT(COMPRESS_LEVEL_OFFSET) - 1);
 			fi->i_cluster_size = 1 << fi->i_log_cluster_size;
 			set_inode_flag(inode, FI_COMPRESSED_FILE);
 		}
@@ -686,13 +692,17 @@ void f2fs_update_inode(struct inode *inode, struct page *node_page)
 		if (f2fs_sb_has_compression(F2FS_I_SB(inode)) &&
 			F2FS_FITS_IN_INODE(ri, F2FS_I(inode)->i_extra_isize,
 							i_log_cluster_size)) {
+			unsigned short compress_flag;
+
 			ri->i_compr_blocks =
 				cpu_to_le64(atomic_read(
 					&F2FS_I(inode)->i_compr_blocks));
 			ri->i_compress_algorithm =
 				F2FS_I(inode)->i_compress_algorithm;
-			ri->i_compress_flag =
-				cpu_to_le16(F2FS_I(inode)->i_compress_flag);
+			compress_flag = F2FS_I(inode)->i_compress_flag |
+				F2FS_I(inode)->i_compress_level <<
+						COMPRESS_LEVEL_OFFSET;
+			ri->i_compress_flag = cpu_to_le16(compress_flag);
 			ri->i_log_cluster_size =
 				F2FS_I(inode)->i_log_cluster_size;
 		}