f2fs: add sysfs entries to select the gc policy

Add sysfs entry gc_idle to control the gc policy. Where
gc_idle = 1 corresponds to selecting a cost benefit approach,
while gc_idle = 2 corresponds to selecting a greedy approach
to garbage collection. The selection is mutually exclusive one
approach will work at any point. If gc_idle = 0, then this
option is disabled.

Cc: Gu Zheng <[e-mail]>
Signed-off-by: Namjae Jeon <[e-mail]>
Signed-off-by: Pankaj Kumar <[e-mail]>
Reviewed-by: Gu Zheng <[e-mail]>
[Jaegeuk Kim: change the select_gc_type() flow slightly]
Signed-off-by: Jaegeuk Kim <[e-mail]>

Documentation/ABI/testing/sysfs-fs-f2fs

···
 Description:
 		 Controls the default sleep time for gc_thread. Time
 		 is in milliseconds.
+
+What:		/sys/fs/f2fs/<disk>/gc_idle
+Date:		July 2013
+Contact:	"Namjae Jeon" <[e-mail]>
+Description:
+		 Controls the victim selection policy for garbage collection.

Documentation/filesystems/f2fs.txt

···
                               time for the garbage collection thread. Time is
                               in milliseconds.
 
+ gc_idle                      This parameter controls the selection of victim
+                              policy for garbage collection. Setting gc_idle = 0
+                              (default) will disable this option. Setting
+                              gc_idle = 1 will select the Cost Benefit approach
+                              & setting gc_idle = 2 will select the greedy aproach.
+
 ================================================================================
 USAGE
 ================================================================================

fs/f2fs/gc.c

···
 	gc_th->max_sleep_time = DEF_GC_THREAD_MAX_SLEEP_TIME;
 	gc_th->no_gc_sleep_time = DEF_GC_THREAD_NOGC_SLEEP_TIME;
 
+	gc_th->gc_idle = 0;
+
 	sbi->gc_thread = gc_th;
 	init_waitqueue_head(&sbi->gc_thread->gc_wait_queue_head);
 	sbi->gc_thread->f2fs_gc_task = kthread_run(gc_thread_func, sbi,
···
 	sbi->gc_thread = NULL;
 }
 
-static int select_gc_type(int gc_type)
+static int select_gc_type(struct f2fs_gc_kthread *gc_th, int gc_type)
 {
-	return (gc_type == BG_GC) ? GC_CB : GC_GREEDY;
+	int gc_mode = (gc_type == BG_GC) ? GC_CB : GC_GREEDY;
+
+	if (gc_th && gc_th->gc_idle) {
+		if (gc_th->gc_idle == 1)
+			gc_mode = GC_CB;
+		else if (gc_th->gc_idle == 2)
+			gc_mode = GC_GREEDY;
+	}
+	return gc_mode;
 }
 
 static void select_policy(struct f2fs_sb_info *sbi, int gc_type,
···
 		p->dirty_segmap = dirty_i->dirty_segmap[type];
 		p->ofs_unit = 1;
 	} else {
-		p->gc_mode = select_gc_type(gc_type);
+		p->gc_mode = select_gc_type(sbi->gc_thread, gc_type);
 		p->dirty_segmap = dirty_i->dirty_segmap[DIRTY];
 		p->ofs_unit = sbi->segs_per_sec;
 	}

fs/f2fs/gc.h

···
 	unsigned int min_sleep_time;
 	unsigned int max_sleep_time;
 	unsigned int no_gc_sleep_time;
+
+	/* for changing gc mode */
+	unsigned int gc_idle;
 };
 
 struct inode_entry {

fs/f2fs/super.c

···
 F2FS_RW_ATTR(gc_min_sleep_time, min_sleep_time);
 F2FS_RW_ATTR(gc_max_sleep_time, max_sleep_time);
 F2FS_RW_ATTR(gc_no_gc_sleep_time, no_gc_sleep_time);
+F2FS_RW_ATTR(gc_idle, gc_idle);
 
 #define ATTR_LIST(name) (&f2fs_attr_##name.attr)
 static struct attribute *f2fs_attrs[] = {
 	ATTR_LIST(gc_min_sleep_time),
 	ATTR_LIST(gc_max_sleep_time),
 	ATTR_LIST(gc_no_gc_sleep_time),
+	ATTR_LIST(gc_idle),
 	NULL,
 };