f2fs: introduce migration_window_granularity

We can control the scanning window granularity for GC migration. For
more frequent scanning and GC on zoned devices, we need a fine grained
control knob for it.
Signed-off-by: Daeho Jeong <daehojeong@google.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Documentation/ABI/testing/sysfs-fs-f2fs

@@ -783,3 +783,11 @@ Description:	The zone UFS we are currently using consists of two parts:
 		blkzone_alloc_policy = 1  Only allow writing to sequential zones
 		blkzone_alloc_policy = 2  Prioritize writing to conventional zones
 		========================  =========================================
+
+What:		/sys/fs/f2fs/<disk>/migration_window_granularity
+Date:		September 2024
+Contact:	"Daeho Jeong" <daehojeong@google.com>
+Description:	Controls migration window granularity of garbage collection on large
+		section. it can control the scanning window granularity for GC migration
+		in a unit of segment, while migration_granularity controls the number
+		of segments which can be migrated at the same turn.

fs/f2fs/f2fs.h

@@ -1696,6 +1696,8 @@ struct f2fs_sb_info {
 	unsigned int max_victim_search;
 	/* migration granularity of garbage collection, unit: segment */
 	unsigned int migration_granularity;
+	/* migration window granularity of garbage collection, unit: segment */
+	unsigned int migration_window_granularity;
 
 	/*
 	 * for stat information.

fs/f2fs/gc.c

@@ -1708,24 +1708,34 @@ static int do_garbage_collect(struct f2fs_sb_info *sbi,
 	struct blk_plug plug;
 	unsigned int segno = start_segno;
 	unsigned int end_segno = start_segno + SEGS_PER_SEC(sbi);
+	unsigned int sec_end_segno;
 	int seg_freed = 0, migrated = 0;
 	unsigned char type = IS_DATASEG(get_seg_entry(sbi, segno)->type) ?
 						SUM_TYPE_DATA : SUM_TYPE_NODE;
 	unsigned char data_type = (type == SUM_TYPE_DATA) ? DATA : NODE;
 	int submitted = 0;
 
-	if (__is_large_section(sbi))
-		end_segno = rounddown(end_segno, SEGS_PER_SEC(sbi));
+	if (__is_large_section(sbi)) {
+		sec_end_segno = rounddown(end_segno, SEGS_PER_SEC(sbi));
 
-	/*
-	 * zone-capacity can be less than zone-size in zoned devices,
-	 * resulting in less than expected usable segments in the zone,
-	 * calculate the end segno in the zone which can be garbage collected
-	 */
-	if (f2fs_sb_has_blkzoned(sbi))
-		end_segno -= SEGS_PER_SEC(sbi) -
+		/*
+		 * zone-capacity can be less than zone-size in zoned devices,
+		 * resulting in less than expected usable segments in the zone,
+		 * calculate the end segno in the zone which can be garbage
+		 * collected
+		 */
+		if (f2fs_sb_has_blkzoned(sbi))
+			sec_end_segno -= SEGS_PER_SEC(sbi) -
 					f2fs_usable_segs_in_sec(sbi, segno);
 
+		if (gc_type == BG_GC)
+			end_segno = start_segno +
+				sbi->migration_window_granularity;
+
+		if (end_segno > sec_end_segno)
+			end_segno = sec_end_segno;
+	}
+
 	sanity_check_seg_type(sbi, get_seg_entry(sbi, segno)->type);
 
 	/* readahead multi ssa blocks those have contiguous address */
@@ -1803,7 +1813,8 @@ static int do_garbage_collect(struct f2fs_sb_info *sbi,
 
 		if (__is_large_section(sbi))
 			sbi->next_victim_seg[gc_type] =
-				(segno + 1 < end_segno) ? segno + 1 : NULL_SEGNO;
+				(segno + 1 < sec_end_segno) ?
+					segno + 1 : NULL_SEGNO;
 skip:
 		f2fs_put_page(sum_page, 0);
 	}

fs/f2fs/gc.h

@@ -32,6 +32,7 @@
 
 #define LIMIT_NO_ZONED_GC	60 /* percentage over total user space of no gc for zoned devices */
 #define LIMIT_BOOST_ZONED_GC	25 /* percentage over total user space of boosted gc for zoned devices */
+#define DEF_MIGRATION_WINDOW_GRANULARITY_ZONED	3
 
 #define DEF_GC_FAILED_PINNED_FILES	2048
 #define MAX_GC_FAILED_PINNED_FILES	USHRT_MAX

fs/f2fs/super.c

@@ -3807,6 +3807,8 @@ static void init_sb_info(struct f2fs_sb_info *sbi)
 	sbi->next_victim_seg[FG_GC] = NULL_SEGNO;
 	sbi->max_victim_search = DEF_MAX_VICTIM_SEARCH;
 	sbi->migration_granularity = SEGS_PER_SEC(sbi);
+	sbi->migration_window_granularity = f2fs_sb_has_blkzoned(sbi) ?
+		DEF_MIGRATION_WINDOW_GRANULARITY_ZONED : SEGS_PER_SEC(sbi);
 	sbi->seq_file_ra_mul = MIN_RA_MUL;
 	sbi->max_fragment_chunk = DEF_FRAGMENT_SIZE;
 	sbi->max_fragment_hole = DEF_FRAGMENT_SIZE;

fs/f2fs/sysfs.c

@@ -564,6 +564,11 @@ static ssize_t __sbi_store(struct f2fs_attr *a,
 			return -EINVAL;
 	}
 
+	if (!strcmp(a->attr.name, "migration_window_granularity")) {
+		if (t == 0 || t > SEGS_PER_SEC(sbi))
+			return -EINVAL;
+	}
+
 	if (!strcmp(a->attr.name, "gc_urgent")) {
 		if (t == 0) {
 			sbi->gc_mode = GC_NORMAL;
@@ -1013,6 +1018,7 @@ F2FS_SBI_RW_ATTR(gc_pin_file_thresh, gc_pin_file_threshold);
 F2FS_SBI_RW_ATTR(gc_reclaimed_segments, gc_reclaimed_segs);
 F2FS_SBI_GENERAL_RW_ATTR(max_victim_search);
 F2FS_SBI_GENERAL_RW_ATTR(migration_granularity);
+F2FS_SBI_GENERAL_RW_ATTR(migration_window_granularity);
 F2FS_SBI_GENERAL_RW_ATTR(dir_level);
 #ifdef CONFIG_F2FS_IOSTAT
 F2FS_SBI_GENERAL_RW_ATTR(iostat_enable);
@@ -1154,6 +1160,7 @@ static struct attribute *f2fs_attrs[] = {
 	ATTR_LIST(min_ssr_sections),
 	ATTR_LIST(max_victim_search),
 	ATTR_LIST(migration_granularity),
+	ATTR_LIST(migration_window_granularity),
 	ATTR_LIST(dir_level),
 	ATTR_LIST(ram_thresh),
 	ATTR_LIST(ra_nid_pages),