f2fs: add the flush_merge handle in the remount flow

Add the *remount* handle of flush_merge option, so that the users
can enable flush_merge in the runtime, such as the underlying device
handles the cache_flush command relatively slowly.

Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

fs/f2fs/f2fs.h

@@ -1177,6 +1177,7 @@ void destroy_node_manager_caches(void);
  */
 void f2fs_balance_fs(struct f2fs_sb_info *);
 void f2fs_balance_fs_bg(struct f2fs_sb_info *);
+int issue_flush_thread(void *);
 int f2fs_issue_flush(struct f2fs_sb_info *);
 void invalidate_blocks(struct f2fs_sb_info *, block_t);
 void refresh_sit_entry(struct f2fs_sb_info *, block_t, block_t);

fs/f2fs/segment.c

@@ -197,7 +197,7 @@ void f2fs_balance_fs_bg(struct f2fs_sb_info *sbi)
 		f2fs_sync_fs(sbi->sb, true);
 }
 
-static int issue_flush_thread(void *data)
+int issue_flush_thread(void *data)
 {
 	struct f2fs_sb_info *sbi = data;
 	struct f2fs_sm_info *sm_i = SM_I(sbi);

fs/f2fs/super.c

@@ -594,6 +594,8 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
 	struct f2fs_sb_info *sbi = F2FS_SB(sb);
 	struct f2fs_mount_info org_mount_opt;
 	int err, active_logs;
+	bool need_restart_gc = false;
+	bool need_stop_gc = false;
 
 	sync_filesystem(sb);
 
@@ -611,7 +613,7 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
 
 	/*
 	 * Previous and new state of filesystem is RO,
-	 * so no point in checking GC conditions.
+	 * so skip checking GC and FLUSH_MERGE conditions.
 	 */
 	if ((sb->s_flags & MS_RDONLY) && (*flags & MS_RDONLY))
 		goto skip;
@@ -625,18 +627,57 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
 		if (sbi->gc_thread) {
 			stop_gc_thread(sbi);
 			f2fs_sync_fs(sb, 1);
+			need_restart_gc = true;
 		}
 	} else if (test_opt(sbi, BG_GC) && !sbi->gc_thread) {
 		err = start_gc_thread(sbi);
 		if (err)
 			goto restore_opts;
+		need_stop_gc = true;
+	}
+
+	/*
+	 * We stop issue flush thread if FS is mounted as RO
+	 * or if flush_merge is not passed in mount option.
+	 */
+	if ((*flags & MS_RDONLY) || !test_opt(sbi, FLUSH_MERGE)) {
+		struct f2fs_sm_info *sm_info = sbi->sm_info;
+
+		if (sm_info->f2fs_issue_flush)
+			kthread_stop(sm_info->f2fs_issue_flush);
+		sm_info->issue_list = sm_info->dispatch_list = NULL;
+		sm_info->f2fs_issue_flush = NULL;
+	} else if (test_opt(sbi, FLUSH_MERGE)) {
+		struct f2fs_sm_info *sm_info = sbi->sm_info;
+
+		if (!sm_info->f2fs_issue_flush) {
+			dev_t dev = sbi->sb->s_bdev->bd_dev;
+
+			spin_lock_init(&sm_info->issue_lock);
+			init_waitqueue_head(&sm_info->flush_wait_queue);
+			sm_info->f2fs_issue_flush =
+				kthread_run(issue_flush_thread, sbi,
+				"f2fs_flush-%u:%u", MAJOR(dev), MINOR(dev));
+			if (IS_ERR(sm_info->f2fs_issue_flush)) {
+				err = PTR_ERR(sm_info->f2fs_issue_flush);
+				sm_info->f2fs_issue_flush = NULL;
+				goto restore_gc;
+			}
+		}
 	}
 skip:
 	/* Update the POSIXACL Flag */
 	 sb->s_flags = (sb->s_flags & ~MS_POSIXACL) |
 		(test_opt(sbi, POSIX_ACL) ? MS_POSIXACL : 0);
 	return 0;
-
+restore_gc:
+	if (need_restart_gc) {
+		if (start_gc_thread(sbi))
+			f2fs_msg(sbi->sb, KERN_WARNING,
+				"background gc thread is stop");
+	} else if (need_stop_gc) {
+		stop_gc_thread(sbi);
+	}
 restore_opts:
 	sbi->mount_opt = org_mount_opt;
 	sbi->active_logs = active_logs;