f2fs: introduce gc_merge mount option

In this patch, we will add two new mount options: "gc_merge" and
"nogc_merge", when background_gc is on, "gc_merge" option can be
set to let background GC thread to handle foreground GC requests,
it can eliminate the sluggish issue caused by slow foreground GC
operation when GC is triggered from a process with limited I/O
and CPU resources.

Original idea is from Xiang.

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

1 files changed, 22 insertions, 4 deletions

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index a2ca483f9855..5c48825fd12d 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -31,19 +31,24 @@ static int gc_thread_func(void *data)
 	struct f2fs_sb_info *sbi = data;
 	struct f2fs_gc_kthread *gc_th = sbi->gc_thread;
 	wait_queue_head_t *wq = &sbi->gc_thread->gc_wait_queue_head;
+	wait_queue_head_t *fggc_wq = &sbi->gc_thread->fggc_wq;
 	unsigned int wait_ms;
 
 	wait_ms = gc_th->min_sleep_time;
 
 	set_freezable();
 	do {
-		bool sync_mode;
+		bool sync_mode, foreground = false;
 
 		wait_event_interruptible_timeout(*wq,
 				kthread_should_stop() || freezing(current) ||
+				waitqueue_active(fggc_wq) ||
 				gc_th->gc_wake,
 				msecs_to_jiffies(wait_ms));
 
+		if (test_opt(sbi, GC_MERGE) && waitqueue_active(fggc_wq))
+			foreground = true;
+
 		/* give it a try one time */
 		if (gc_th->gc_wake)
 			gc_th->gc_wake = 0;
@@ -90,7 +95,10 @@ static int gc_thread_func(void *data)
 			goto do_gc;
 		}
 
-		if (!down_write_trylock(&sbi->gc_lock)) {
+		if (foreground) {
+			down_write(&sbi->gc_lock);
+			goto do_gc;
+		} else if (!down_write_trylock(&sbi->gc_lock)) {
 			stat_other_skip_bggc_count(sbi);
 			goto next;
 		}
@@ -107,14 +115,22 @@ static int gc_thread_func(void *data)
 		else
 			increase_sleep_time(gc_th, &wait_ms);
 do_gc:
-		stat_inc_bggc_count(sbi->stat_info);
+		if (!foreground)
+			stat_inc_bggc_count(sbi->stat_info);
 
 		sync_mode = F2FS_OPTION(sbi).bggc_mode == BGGC_MODE_SYNC;
 
+		/* foreground GC was been triggered via f2fs_balance_fs() */
+		if (foreground)
+			sync_mode = false;
+
 		/* if return value is not zero, no victim was selected */
-		if (f2fs_gc(sbi, sync_mode, true, false, NULL_SEGNO))
+		if (f2fs_gc(sbi, sync_mode, !foreground, false, NULL_SEGNO))
 			wait_ms = gc_th->no_gc_sleep_time;
 
+		if (foreground)
+			wake_up_all(&gc_th->fggc_wq);
+
 		trace_f2fs_background_gc(sbi->sb, wait_ms,
 				prefree_segments(sbi), free_segments(sbi));
 
@@ -148,6 +164,7 @@ int f2fs_start_gc_thread(struct f2fs_sb_info *sbi)
 
 	sbi->gc_thread = gc_th;
 	init_waitqueue_head(&sbi->gc_thread->gc_wait_queue_head);
+	init_waitqueue_head(&sbi->gc_thread->fggc_wq);
 	sbi->gc_thread->f2fs_gc_task = kthread_run(gc_thread_func, sbi,
 			"f2fs_gc-%u:%u", MAJOR(dev), MINOR(dev));
 	if (IS_ERR(gc_th->f2fs_gc_task)) {
@@ -165,6 +182,7 @@ void f2fs_stop_gc_thread(struct f2fs_sb_info *sbi)
 	if (!gc_th)
 		return;
 	kthread_stop(gc_th->f2fs_gc_task);
+	wake_up_all(&gc_th->fggc_wq);
 	kfree(gc_th);
 	sbi->gc_thread = NULL;
 }