f2fs: introduce reserved_pin_section sysfs entry

This patch introduces /sys/fs/f2fs/<dev>/reserved_pin_section for tuning
@Needed parameter of has_not_enough_free_secs(), if we configure it w/
zero, it can avoid f2fs_gc() as much as possible while fallocating on
pinned file.

Signed-off-by: Chao Yu <[email protected]>
Reviewed-by: wangzijie <[email protected]>
Signed-off-by: Jaegeuk Kim <[email protected]>

Author: chaseyu

Documentation/ABI/testing/sysfs-fs-f2fs

@@ -861,3 +861,12 @@ Description:	This is a read-only entry to show the value of sb.s_encoding_flags,
 		SB_ENC_STRICT_MODE_FL            0x00000001
 		SB_ENC_NO_COMPAT_FALLBACK_FL     0x00000002
 		============================     ==========
+
+What:		/sys/fs/f2fs/<disk>/reserved_pin_section
+Date:		June 2025
+Contact:	"Chao Yu" <[email protected]>
+Description:	This threshold is used to control triggering garbage collection while
+		fallocating on pinned file, so, it can guarantee there is enough free
+		reserved section before preallocating on pinned file.
+		By default, the value is ovp_sections, especially, for zoned ufs, the
+		value is 1.

fs/f2fs/f2fs.h

@@ -1724,6 +1724,9 @@ struct f2fs_sb_info {
 	/* for skip statistic */
 	unsigned long long skipped_gc_rwsem;		/* FG_GC only */
 
+	/* free sections reserved for pinned file */
+	unsigned int reserved_pin_section;
+
 	/* threshold for gc trials on pinned files */
 	unsigned short gc_pin_file_threshold;
 	struct f2fs_rwsem pin_sem;

fs/f2fs/file.c

@@ -1887,9 +1887,8 @@ static int f2fs_expand_inode_data(struct inode *inode, loff_t offset,
 			}
 		}
 
-		if (has_not_enough_free_secs(sbi, 0, f2fs_sb_has_blkzoned(sbi) ?
-			ZONED_PIN_SEC_REQUIRED_COUNT :
-			GET_SEC_FROM_SEG(sbi, overprovision_segments(sbi)))) {
+		if (has_not_enough_free_secs(sbi, 0,
+				sbi->reserved_pin_section)) {
 			f2fs_down_write(&sbi->gc_lock);
 			stat_inc_gc_call_count(sbi, FOREGROUND);
 			err = f2fs_gc(sbi, &gc_control);

fs/f2fs/super.c

@@ -4771,6 +4771,10 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
 	/* get segno of first zoned block device */
 	sbi->first_seq_zone_segno = get_first_seq_zone_segno(sbi);
 
+	sbi->reserved_pin_section = f2fs_sb_has_blkzoned(sbi) ?
+			ZONED_PIN_SEC_REQUIRED_COUNT :
+			GET_SEC_FROM_SEG(sbi, overprovision_segments(sbi));
+
 	/* Read accumulated write IO statistics if exists */
 	seg_i = CURSEG_I(sbi, CURSEG_HOT_NODE);
 	if (__exist_node_summaries(sbi))

fs/f2fs/sysfs.c

@@ -824,6 +824,13 @@ static ssize_t __sbi_store(struct f2fs_attr *a,
 		return count;
 	}
 
+	if (!strcmp(a->attr.name, "reserved_pin_section")) {
+		if (t > GET_SEC_FROM_SEG(sbi, overprovision_segments(sbi)))
+			return -EINVAL;
+		*ui = (unsigned int)t;
+		return count;
+	}
+
 	*ui = (unsigned int)t;
 
 	return count;
@@ -1130,6 +1137,7 @@ F2FS_SBI_GENERAL_RO_ATTR(unusable_blocks_per_sec);
 F2FS_SBI_GENERAL_RW_ATTR(blkzone_alloc_policy);
 #endif
 F2FS_SBI_GENERAL_RW_ATTR(carve_out);
+F2FS_SBI_GENERAL_RW_ATTR(reserved_pin_section);
 
 /* STAT_INFO ATTR */
 #ifdef CONFIG_F2FS_STAT_FS
@@ -1323,6 +1331,7 @@ static struct attribute *f2fs_attrs[] = {
 	ATTR_LIST(last_age_weight),
 	ATTR_LIST(max_read_extent_count),
 	ATTR_LIST(carve_out),
+	ATTR_LIST(reserved_pin_section),
 	NULL,
 };
 ATTRIBUTE_GROUPS(f2fs);