f2fs: add mount option for segment allocation policy

This patch adds an mount option, "alloc_mode=%s" having two options, "default"
and "reuse".

In "alloc_mode=reuse" case, f2fs starts to allocate segments from 0'th segment
all the time to reassign segments. It'd be useful for small-sized eMMC parts.

Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Documentation/filesystems/f2fs.txt

@@ -180,6 +180,8 @@ whint_mode=%s          Control which write hints are passed down to block
                        down hints. In "user-based" mode, f2fs tries to pass
                        down hints given by users. And in "fs-based" mode, f2fs
                        passes down hints with its policy.
+alloc_mode=%s          Adjust block allocation policy, which supports "reuse"
+                       and "default".
 
 ================================================================================
 DEBUGFS ENTRIES

fs/f2fs/f2fs.h

@@ -1043,6 +1043,11 @@ enum {
 	WHINT_MODE_FS,		/* pass down hints with F2FS policy */
 };
 
+enum {
+	ALLOC_MODE_DEFAULT,	/* stay default */
+	ALLOC_MODE_REUSE,	/* reuse segments as much as possible */
+};
+
 struct f2fs_sb_info {
 	struct super_block *sb;			/* pointer to VFS super block */
 	struct proc_dir_entry *s_proc;		/* proc entry */
@@ -1229,6 +1234,9 @@ struct f2fs_sb_info {
 #endif
 	/* For which write hints are passed down to block layer */
 	int whint_mode;
+
+	/* segment allocation policy */
+	int alloc_mode;
 };
 
 #ifdef CONFIG_F2FS_FAULT_INJECTION

fs/f2fs/segment.c

@@ -2170,6 +2170,11 @@ static unsigned int __get_next_segno(struct f2fs_sb_info *sbi, int type)
 
 	if (SIT_I(sbi)->last_victim[ALLOC_NEXT])
 		return SIT_I(sbi)->last_victim[ALLOC_NEXT];
+
+	/* find segments from 0 to reuse freed segments */
+	if (sbi->alloc_mode == ALLOC_MODE_REUSE)
+		return 0;
+
 	return CURSEG_I(sbi, type)->segno;
 }
 

fs/f2fs/super.c

@@ -130,6 +130,7 @@ enum {
 	Opt_jqfmt_vfsv0,
 	Opt_jqfmt_vfsv1,
 	Opt_whint,
+	Opt_alloc,
 	Opt_err,
 };
 
@@ -184,6 +185,7 @@ static match_table_t f2fs_tokens = {
 	{Opt_jqfmt_vfsv0, "jqfmt=vfsv0"},
 	{Opt_jqfmt_vfsv1, "jqfmt=vfsv1"},
 	{Opt_whint, "whint_mode=%s"},
+	{Opt_alloc, "alloc_mode=%s"},
 	{Opt_err, NULL},
 };
 
@@ -700,6 +702,23 @@ static int parse_options(struct super_block *sb, char *options)
 			}
 			kfree(name);
 			break;
+		case Opt_alloc:
+			name = match_strdup(&args[0]);
+			if (!name)
+				return -ENOMEM;
+
+			if (strlen(name) == 7 &&
+					!strncmp(name, "default", 7)) {
+				sbi->alloc_mode = ALLOC_MODE_DEFAULT;
+			} else if (strlen(name) == 5 &&
+					!strncmp(name, "reuse", 5)) {
+				sbi->alloc_mode = ALLOC_MODE_REUSE;
+			} else {
+				kfree(name);
+				return -EINVAL;
+			}
+			kfree(name);
+			break;
 		default:
 			f2fs_msg(sb, KERN_ERR,
 				"Unrecognized mount option \"%s\" or missing value",
@@ -1264,6 +1283,10 @@ static int f2fs_show_options(struct seq_file *seq, struct dentry *root)
 	else if (sbi->whint_mode == WHINT_MODE_FS)
 		seq_printf(seq, ",whint_mode=%s", "fs-based");
 
+	if (sbi->alloc_mode == ALLOC_MODE_DEFAULT)
+		seq_printf(seq, ",alloc_mode=%s", "default");
+	else if (sbi->alloc_mode == ALLOC_MODE_REUSE)
+		seq_printf(seq, ",alloc_mode=%s", "reuse");
 	return 0;
 }
 
@@ -1273,6 +1296,7 @@ static void default_options(struct f2fs_sb_info *sbi)
 	sbi->active_logs = NR_CURSEG_TYPE;
 	sbi->inline_xattr_size = DEFAULT_INLINE_XATTR_ADDRS;
 	sbi->whint_mode = WHINT_MODE_OFF;
+	sbi->alloc_mode = ALLOC_MODE_DEFAULT;
 
 	set_opt(sbi, BG_GC);
 	set_opt(sbi, INLINE_XATTR);
@@ -1314,6 +1338,7 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
 	bool need_stop_gc = false;
 	bool no_extent_cache = !test_opt(sbi, EXTENT_CACHE);
 	int old_whint_mode = sbi->whint_mode;
+	int old_alloc_mode = sbi->alloc_mode;
 #ifdef CONFIG_F2FS_FAULT_INJECTION
 	struct f2fs_fault_info ffi = sbi->fault_info;
 #endif
@@ -1463,6 +1488,7 @@ restore_opts:
 		sbi->s_qf_names[i] = s_qf_names[i];
 	}
 #endif
+	sbi->alloc_mode = old_alloc_mode;
 	sbi->whint_mode = old_whint_mode;
 	sbi->mount_opt = org_mount_opt;
 	sbi->active_logs = active_logs;