f2fs: introduce memory mode

Introduce memory mode to supports "normal" and "low" memory modes.
"low" mode is to support low memory devices. Because of the nature of
low memory devices, in this mode, f2fs will try to save memory sometimes
by sacrificing performance. "normal" mode is the default mode and same
as before.
Signed-off-by: Daeho Jeong <daehojeong@google.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Documentation/filesystems/f2fs.rst

@@ -336,6 +336,11 @@ discard_unit=%s		 Control discard unit, the argument can be "block", "segment"
 			 default, it is helpful for large sized SMR or ZNS devices to
 			 reduce memory cost by getting rid of fs metadata supports small
 			 discard.
+memory=%s		 Control memory mode. This supports "normal" and "low" modes.
+			 "low" mode is introduced to support low memory devices.
+			 Because of the nature of low memory devices, in this mode, f2fs
+			 will try to save memory sometimes by sacrificing performance.
+			 "normal" mode is the default mode and same as before.
 ======================== ============================================================
 
 Debugfs Entries

fs/f2fs/f2fs.h

@@ -159,6 +159,7 @@ struct f2fs_mount_info {
 	int fsync_mode;			/* fsync policy */
 	int fs_mode;			/* fs mode: LFS or ADAPTIVE */
 	int bggc_mode;			/* bggc mode: off, on or sync */
+	int memory_mode;		/* memory mode */
 	int discard_unit;		/*
 					 * discard command's offset/size should
 					 * be aligned to this unit: block,
@@ -1360,6 +1361,13 @@ enum {
 	DISCARD_UNIT_SECTION,	/* basic discard unit is section */
 };
 
+enum {
+	MEMORY_MODE_NORMAL,	/* memory mode for normal devices */
+	MEMORY_MODE_LOW,	/* memory mode for low memry devices */
+};
+
+
+
 static inline int f2fs_test_bit(unsigned int nr, char *addr);
 static inline void f2fs_set_bit(unsigned int nr, char *addr);
 static inline void f2fs_clear_bit(unsigned int nr, char *addr);
@@ -4398,6 +4406,11 @@ static inline bool f2fs_lfs_mode(struct f2fs_sb_info *sbi)
 	return F2FS_OPTION(sbi).fs_mode == FS_MODE_LFS;
 }
 
+static inline bool f2fs_low_mem_mode(struct f2fs_sb_info *sbi)
+{
+	return F2FS_OPTION(sbi).memory_mode == MEMORY_MODE_LOW;
+}
+
 static inline bool f2fs_may_compress(struct inode *inode)
 {
 	if (IS_SWAPFILE(inode) || f2fs_is_pinned_file(inode) ||

fs/f2fs/super.c

@@ -160,6 +160,7 @@ enum {
 	Opt_gc_merge,
 	Opt_nogc_merge,
 	Opt_discard_unit,
+	Opt_memory_mode,
 	Opt_err,
 };
 
@@ -236,6 +237,7 @@ static match_table_t f2fs_tokens = {
 	{Opt_gc_merge, "gc_merge"},
 	{Opt_nogc_merge, "nogc_merge"},
 	{Opt_discard_unit, "discard_unit=%s"},
+	{Opt_memory_mode, "memory=%s"},
 	{Opt_err, NULL},
 };
 
@@ -1235,6 +1237,22 @@ static int parse_options(struct super_block *sb, char *options, bool is_remount)
 			}
 			kfree(name);
 			break;
+		case Opt_memory_mode:
+			name = match_strdup(&args[0]);
+			if (!name)
+				return -ENOMEM;
+			if (!strcmp(name, "normal")) {
+				F2FS_OPTION(sbi).memory_mode =
+						MEMORY_MODE_NORMAL;
+			} else if (!strcmp(name, "low")) {
+				F2FS_OPTION(sbi).memory_mode =
+						MEMORY_MODE_LOW;
+			} else {
+				kfree(name);
+				return -EINVAL;
+			}
+			kfree(name);
+			break;
 		default:
 			f2fs_err(sbi, "Unrecognized mount option \"%s\" or missing value",
 				 p);
@@ -2006,6 +2024,11 @@ static int f2fs_show_options(struct seq_file *seq, struct dentry *root)
 	else if (F2FS_OPTION(sbi).discard_unit == DISCARD_UNIT_SECTION)
 		seq_printf(seq, ",discard_unit=%s", "section");
 
+	if (F2FS_OPTION(sbi).memory_mode == MEMORY_MODE_NORMAL)
+		seq_printf(seq, ",memory=%s", "normal");
+	else if (F2FS_OPTION(sbi).memory_mode == MEMORY_MODE_LOW)
+		seq_printf(seq, ",memory=%s", "low");
+
 	return 0;
 }
 
@@ -2027,6 +2050,7 @@ static void default_options(struct f2fs_sb_info *sbi)
 	F2FS_OPTION(sbi).compress_ext_cnt = 0;
 	F2FS_OPTION(sbi).compress_mode = COMPR_MODE_FS;
 	F2FS_OPTION(sbi).bggc_mode = BGGC_MODE_ON;
+	F2FS_OPTION(sbi).memory_mode = MEMORY_MODE_NORMAL;
 
 	sbi->sb->s_flags &= ~SB_INLINECRYPT;