[PATCH 2/5] f2fs: add cur_victim_sec for BG_GC to avoid skipping BG_GC victim

[Yunlong Song]

If f2fs aborts BG_GC, then the section bit of victim_secmap will be set,
which will cause the section skipped in the future get_victim of BG_GC.
In a worst case that each section in the victim_secmap is set and there
are enough free sections (so FG_GC can not be triggered), then BG_GC
will skip all the sections and cannot find any victims, causing BG_GC
failed each time. Besides, SSR also uses BG_GC to get ssr segment, if
many sections in the victim_secmap are set, then SSR cannot get a proper
ssr segment to allocate blocks, which makes SSR inefficiently. To fix
this problem, we can add cur_victim_sec for BG_GC similar like that in
FG_GC to avoid selecting the same section repeatedly.

Signed-off-by: Yunlong Song <yunlong.song@xxxxxxxxxx>
---
 fs/f2fs/f2fs.h              |  3 ++-
 fs/f2fs/gc.c                | 15 +++++++++------
 fs/f2fs/segment.h           |  3 ++-
 fs/f2fs/super.c             |  3 ++-
 include/trace/events/f2fs.h | 18 ++++++++++++------
 5 files changed, 27 insertions(+), 15 deletions(-)

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 57a8851..f8a7b42 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1217,7 +1217,8 @@ struct f2fs_sb_info {
 	/* for cleaning operations */
 	struct mutex gc_mutex;			/* mutex for GC */
 	struct f2fs_gc_kthread	*gc_thread;	/* GC thread */
-	unsigned int cur_victim_sec;		/* current victim section num */
+	unsigned int cur_fg_victim_sec;		/* current FG_GC victim section num */
+	unsigned int cur_bg_victim_sec;		/* current BG_GC victim section num */
 	unsigned int gc_mode;			/* current GC state */
 	/* for skip statistic */
 	unsigned long long skipped_atomic_files[2];	/* FG_GC and BG_GC */
diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 2ba470d..705d419 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -367,8 +367,6 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
 
 		if (sec_usage_check(sbi, secno))
 			goto next;
-		if (gc_type == BG_GC && test_bit(secno, dirty_i->victim_secmap))
-			goto next;
 
 		cost = get_gc_cost(sbi, segno, &p);
 
@@ -391,14 +389,17 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
 		if (p.alloc_mode == LFS) {
 			secno = GET_SEC_FROM_SEG(sbi, p.min_segno);
 			if (gc_type == FG_GC)
-				sbi->cur_victim_sec = secno;
-			else
+				sbi->cur_fg_victim_sec = secno;
+			else {
 				set_bit(secno, dirty_i->victim_secmap);
+				sbi->cur_bg_victim_sec = secno;
+			}
 		}
 		*result = (p.min_segno / p.ofs_unit) * p.ofs_unit;
 
 		trace_f2fs_get_victim(sbi->sb, type, gc_type, &p,
-				sbi->cur_victim_sec,
+				sbi->cur_fg_victim_sec,
+				sbi->cur_bg_victim_sec,
 				prefree_segments(sbi), free_segments(sbi));
 	}
 out:
@@ -1098,7 +1099,9 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
 	}
 
 	if (gc_type == FG_GC)
-		sbi->cur_victim_sec = NULL_SEGNO;
+		sbi->cur_fg_victim_sec = NULL_SEGNO;
+	else
+		sbi->cur_bg_victim_sec = NULL_SEGNO;
 
 	if (!sync) {
 		if (has_not_enough_free_secs(sbi, sec_freed, 0)) {
diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
index 5049551..b21bb96 100644
--- a/fs/f2fs/segment.h
+++ b/fs/f2fs/segment.h
@@ -787,7 +787,8 @@ static inline block_t sum_blk_addr(struct f2fs_sb_info *sbi, int base, int type)
 
 static inline bool sec_usage_check(struct f2fs_sb_info *sbi, unsigned int secno)
 {
-	if (IS_CURSEC(sbi, secno) || (sbi->cur_victim_sec == secno))
+	if (IS_CURSEC(sbi, secno) || (sbi->cur_fg_victim_sec == secno) ||
+		(sbi->cur_bg_victim_sec == secno))
 		return true;
 	return false;
 }
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 7187885..ef69ebf 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -2386,7 +2386,8 @@ static void init_sb_info(struct f2fs_sb_info *sbi)
 	sbi->root_ino_num = le32_to_cpu(raw_super->root_ino);
 	sbi->node_ino_num = le32_to_cpu(raw_super->node_ino);
 	sbi->meta_ino_num = le32_to_cpu(raw_super->meta_ino);
-	sbi->cur_victim_sec = NULL_SECNO;
+	sbi->cur_fg_victim_sec = NULL_SECNO;
+	sbi->cur_bg_victim_sec = NULL_SECNO;
 	sbi->max_victim_search = DEF_MAX_VICTIM_SEARCH;
 
 	sbi->dir_level = DEF_DIR_LEVEL;
diff --git a/include/trace/events/f2fs.h b/include/trace/events/f2fs.h
index 7956989..0f01f82 100644
--- a/include/trace/events/f2fs.h
+++ b/include/trace/events/f2fs.h
@@ -693,10 +693,12 @@
 TRACE_EVENT(f2fs_get_victim,
 
 	TP_PROTO(struct super_block *sb, int type, int gc_type,
-			struct victim_sel_policy *p, unsigned int pre_victim,
+			struct victim_sel_policy *p, unsigned int pre_fg_victim,
+			unsigned int pre_bg_victim,
 			unsigned int prefree, unsigned int free),
 
-	TP_ARGS(sb, type, gc_type, p, pre_victim, prefree, free),
+	TP_ARGS(sb, type, gc_type, p, pre_fg_victim, pre_bg_victim,
+		prefree, free),
 
 	TP_STRUCT__entry(
 		__field(dev_t,	dev)
@@ -707,7 +709,8 @@
 		__field(unsigned int,	victim)
 		__field(unsigned int,	cost)
 		__field(unsigned int,	ofs_unit)
-		__field(unsigned int,	pre_victim)
+		__field(unsigned int,	pre_fg_victim)
+		__field(unsigned int,	pre_bg_victim)
 		__field(unsigned int,	prefree)
 		__field(unsigned int,	free)
 	),
@@ -721,14 +724,16 @@
 		__entry->victim		= p->min_segno;
 		__entry->cost		= p->min_cost;
 		__entry->ofs_unit	= p->ofs_unit;
-		__entry->pre_victim	= pre_victim;
+		__entry->pre_fg_victim	= pre_fg_victim;
+		__entry->pre_bg_victim	= pre_bg_victim;
 		__entry->prefree	= prefree;
 		__entry->free		= free;
 	),
 
 	TP_printk("dev = (%d,%d), type = %s, policy = (%s, %s, %s), "
 		"victim = %u, cost = %u, ofs_unit = %u, "
-		"pre_victim_secno = %d, prefree = %u, free = %u",
+		"pre_fg_victim_secno = %d, pre_bg_victim_secno = %d, "
+		"prefree = %u, free = %u",
 		show_dev(__entry->dev),
 		show_data_type(__entry->type),
 		show_gc_type(__entry->gc_type),
@@ -737,7 +742,8 @@
 		__entry->victim,
 		__entry->cost,
 		__entry->ofs_unit,
-		(int)__entry->pre_victim,
+		(int)__entry->pre_fg_victim,
+		(int)__entry->pre_bg_victim,
 		__entry->prefree,
 		__entry->free)
 );
-- 
1.8.5.2