f2fs: add gc_boost_gc_multiple sysfs node

Add a sysfs knob to set a multiplier for the background GC migration
window when F2FS Garbage Collection is boosted.

Signed-off-by: Daeho Jeong <daehojeong@google.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Author: Daeho Jeong

Documentation/ABI/testing/sysfs-fs-f2fs

@@ -870,3 +870,10 @@ Description:	This threshold is used to control triggering garbage collection whi
 		reserved section before preallocating on pinned file.
 		By default, the value is ovp_sections, especially, for zoned ufs, the
 		value is 1.
+
+What:		/sys/fs/f2fs/<disk>/gc_boost_gc_multiple
+Date:		June 2025
+Contact:	"Daeho Jeong" <daehojeong@google.com>
+Description:	Set a multiplier for the background GC migration window when F2FS GC is
+		boosted. The range should be from 1 to the segment count in a section.
+		Default: 5

fs/f2fs/gc.c

@@ -197,6 +197,7 @@ int f2fs_start_gc_thread(struct f2fs_sb_info *sbi)
 
 	gc_th->urgent_sleep_time = DEF_GC_THREAD_URGENT_SLEEP_TIME;
 	gc_th->valid_thresh_ratio = DEF_GC_THREAD_VALID_THRESH_RATIO;
+	gc_th->boost_gc_multiple = BOOST_GC_MULTIPLE;
 
 	if (f2fs_sb_has_blkzoned(sbi)) {
 		gc_th->min_sleep_time = DEF_GC_THREAD_MIN_SLEEP_TIME_ZONED;
@@ -1750,7 +1751,7 @@ static int do_garbage_collect(struct f2fs_sb_info *sbi,
 					!has_enough_free_blocks(sbi,
 					sbi->gc_thread->boost_zoned_gc_percent))
 				window_granularity *=
-					BOOST_GC_MULTIPLE;
+					sbi->gc_thread->boost_gc_multiple;
 
 			end_segno = start_segno + window_granularity;
 		}

fs/f2fs/gc.h

@@ -68,6 +68,7 @@ struct f2fs_gc_kthread {
 	unsigned int no_zoned_gc_percent;
 	unsigned int boost_zoned_gc_percent;
 	unsigned int valid_thresh_ratio;
+	unsigned int boost_gc_multiple;
 };
 
 struct gc_inode_list {

fs/f2fs/sysfs.c

@@ -852,6 +852,13 @@ static ssize_t __sbi_store(struct f2fs_attr *a,
 		return count;
 	}
 
+	if (!strcmp(a->attr.name, "gc_boost_gc_multiple")) {
+		if (t < 1 || t > SEGS_PER_SEC(sbi))
+			return -EINVAL;
+		sbi->gc_thread->boost_gc_multiple = (unsigned int)t;
+		return count;
+	}
+
 	*ui = (unsigned int)t;
 
 	return count;
@@ -1078,6 +1085,7 @@ GC_THREAD_RW_ATTR(gc_no_gc_sleep_time, no_gc_sleep_time);
 GC_THREAD_RW_ATTR(gc_no_zoned_gc_percent, no_zoned_gc_percent);
 GC_THREAD_RW_ATTR(gc_boost_zoned_gc_percent, boost_zoned_gc_percent);
 GC_THREAD_RW_ATTR(gc_valid_thresh_ratio, valid_thresh_ratio);
+GC_THREAD_RW_ATTR(gc_boost_gc_multiple, boost_gc_multiple);
 
 /* SM_INFO ATTR */
 SM_INFO_RW_ATTR(reclaim_segments, rec_prefree_segments);
@@ -1249,6 +1257,7 @@ static struct attribute *f2fs_attrs[] = {
 	ATTR_LIST(gc_no_zoned_gc_percent),
 	ATTR_LIST(gc_boost_zoned_gc_percent),
 	ATTR_LIST(gc_valid_thresh_ratio),
+	ATTR_LIST(gc_boost_gc_multiple),
 	ATTR_LIST(gc_idle),
 	ATTR_LIST(gc_urgent),
 	ATTR_LIST(reclaim_segments),