f2fs: introduce f2fs_get_section_mtime

When segs_per_sec is larger than 1, section may contain invalid segments,
mtime should be the average value of each valid blocks,
so introduce f2fs_get_section_mtime to
record the average mtime of all valid blocks in a section.

Signed-off-by: liuderong <liuderong@oppo.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Author: liuderong

fs/f2fs/f2fs.h

@@ -3783,6 +3783,8 @@ enum rw_hint f2fs_io_type_to_rw_hint(struct f2fs_sb_info *sbi,
 unsigned int f2fs_usable_segs_in_sec(struct f2fs_sb_info *sbi);
 unsigned int f2fs_usable_blks_in_seg(struct f2fs_sb_info *sbi,
 			unsigned int segno);
+unsigned long long f2fs_get_section_mtime(struct f2fs_sb_info *sbi,
+			unsigned int segno);
 
 #define DEF_FRAGMENT_SIZE	4
 #define MIN_FRAGMENT_SIZE	1

fs/f2fs/gc.c

@@ -361,20 +361,15 @@ static unsigned int check_bg_victims(struct f2fs_sb_info *sbi)
 static unsigned int get_cb_cost(struct f2fs_sb_info *sbi, unsigned int segno)
 {
 	struct sit_info *sit_i = SIT_I(sbi);
-	unsigned int secno = GET_SEC_FROM_SEG(sbi, segno);
-	unsigned int start = GET_SEG_FROM_SEC(sbi, secno);
 	unsigned long long mtime = 0;
 	unsigned int vblocks;
 	unsigned char age = 0;
 	unsigned char u;
-	unsigned int i;
 	unsigned int usable_segs_per_sec = f2fs_usable_segs_in_sec(sbi);
 
-	for (i = 0; i < usable_segs_per_sec; i++)
-		mtime += get_seg_entry(sbi, start + i)->mtime;
+	mtime = f2fs_get_section_mtime(sbi, segno);
+	f2fs_bug_on(sbi, mtime == INVALID_MTIME);
 	vblocks = get_valid_blocks(sbi, segno, true);
-
-	mtime = div_u64(mtime, usable_segs_per_sec);
 	vblocks = div_u64(vblocks, usable_segs_per_sec);
 
 	u = BLKS_TO_SEGS(sbi, vblocks * 100);
@@ -519,20 +514,16 @@ static void add_victim_entry(struct f2fs_sb_info *sbi,
 				struct victim_sel_policy *p, unsigned int segno)
 {
 	struct sit_info *sit_i = SIT_I(sbi);
-	unsigned int secno = GET_SEC_FROM_SEG(sbi, segno);
-	unsigned int start = GET_SEG_FROM_SEC(sbi, secno);
 	unsigned long long mtime = 0;
-	unsigned int i;
 
 	if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED))) {
 		if (p->gc_mode == GC_AT &&
 			get_valid_blocks(sbi, segno, true) == 0)
 			return;
 	}
 
-	for (i = 0; i < SEGS_PER_SEC(sbi); i++)
-		mtime += get_seg_entry(sbi, start + i)->mtime;
-	mtime = div_u64(mtime, SEGS_PER_SEC(sbi));
+	mtime = f2fs_get_section_mtime(sbi, segno);
+	f2fs_bug_on(sbi, mtime == INVALID_MTIME);
 
 	/* Handle if the system time has changed by the user */
 	if (mtime < sit_i->min_mtime)

fs/f2fs/segment.c

@@ -5430,6 +5430,35 @@ unsigned int f2fs_usable_segs_in_sec(struct f2fs_sb_info *sbi)
 	return SEGS_PER_SEC(sbi);
 }
 
+unsigned long long f2fs_get_section_mtime(struct f2fs_sb_info *sbi,
+	unsigned int segno)
+{
+	unsigned int usable_segs_per_sec = f2fs_usable_segs_in_sec(sbi);
+	unsigned int secno = 0, start = 0;
+	unsigned int total_valid_blocks = 0;
+	unsigned long long mtime = 0;
+	unsigned int i = 0;
+
+	secno = GET_SEC_FROM_SEG(sbi, segno);
+	start = GET_SEG_FROM_SEC(sbi, secno);
+
+	if (!__is_large_section(sbi))
+		return get_seg_entry(sbi, start + i)->mtime;
+
+	for (i = 0; i < usable_segs_per_sec; i++) {
+		/* for large section, only check the mtime of valid segments */
+		struct seg_entry *se = get_seg_entry(sbi, start+i);
+
+		mtime += se->mtime * se->valid_blocks;
+		total_valid_blocks += se->valid_blocks;
+	}
+
+	if (total_valid_blocks == 0)
+		return INVALID_MTIME;
+
+	return div_u64(mtime, total_valid_blocks);
+}
+
 /*
  * Update min, max modified time for cost-benefit GC algorithm
  */
@@ -5443,13 +5472,9 @@ static void init_min_max_mtime(struct f2fs_sb_info *sbi)
 	sit_i->min_mtime = ULLONG_MAX;
 
 	for (segno = 0; segno < MAIN_SEGS(sbi); segno += SEGS_PER_SEC(sbi)) {
-		unsigned int i;
 		unsigned long long mtime = 0;
 
-		for (i = 0; i < SEGS_PER_SEC(sbi); i++)
-			mtime += get_seg_entry(sbi, segno + i)->mtime;
-
-		mtime = div_u64(mtime, SEGS_PER_SEC(sbi));
+		mtime = f2fs_get_section_mtime(sbi, segno);
 
 		if (sit_i->min_mtime > mtime)
 			sit_i->min_mtime = mtime;

fs/f2fs/segment.h

@@ -18,6 +18,8 @@
 #define F2FS_MIN_SEGMENTS	9 /* SB + 2 (CP + SIT + NAT) + SSA + MAIN */
 #define F2FS_MIN_META_SEGMENTS	8 /* SB + 2 (CP + SIT + NAT) + SSA */
 
+#define INVALID_MTIME ULLONG_MAX /* no valid blocks in a segment/section */
+
 /* L: Logical segment # in volume, R: Relative segment # in main area */
 #define GET_L2R_SEGNO(free_i, segno)	((segno) - (free_i)->start_segno)
 #define GET_R2L_SEGNO(free_i, segno)	((segno) + (free_i)->start_segno)