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From:   Daeho Jeong <daeho43@gmail.com>
To:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net, kernel-team@android.com
Cc:     Daeho Jeong <daehojeong@google.com>
Subject: [PATCH 1/2] f2fs: introduce memory mode
Date:   Mon, 20 Jun 2022 10:38:42 -0700
Message-Id: <20220620173843.1462198-1-daeho43@gmail.com>
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From: Daeho Jeong <daehojeong@google.com>

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>
---
 Documentation/filesystems/f2fs.rst |  5 +++++
 fs/f2fs/f2fs.h                     | 13 +++++++++++++
 fs/f2fs/super.c                    | 24 ++++++++++++++++++++++++
 3 files changed, 42 insertions(+)

diff --git a/Documentation/filesystems/f2fs.rst b/Documentation/filesystems/f2fs.rst
index ad8dc8c040a2..2965601e21bb 100644
--- a/Documentation/filesystems/f2fs.rst
+++ b/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
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index d9bbecd008d2..fea97093d927 100644
--- a/fs/f2fs/f2fs.h
+++ b/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) ||
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 3112fe92f934..cf9cf24f9b56 100644
--- a/fs/f2fs/super.c
+++ b/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;
 
-- 
2.37.0.rc0.104.g0611611a94-goog