[PATCH 3/3] f2fs: export migration_granularity sysfs entry

[Chao Yu]

Add one sysfs entry to control migration granularity of GC in large
section f2fs, it can be tuned to mitigate heavy overhead of migrating
huge number of blocks in large section.

Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
---
 Documentation/ABI/testing/sysfs-fs-f2fs | 9 +++++++++
 fs/f2fs/sysfs.c                         | 7 +++++++
 2 files changed, 16 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs b/Documentation/ABI/testing/sysfs-fs-f2fs
index 3ac41774ad3c..a7ce33199457 100644
--- a/Documentation/ABI/testing/sysfs-fs-f2fs
+++ b/Documentation/ABI/testing/sysfs-fs-f2fs
@@ -92,6 +92,15 @@ Contact:	"Jaegeuk Kim" <jaegeuk.kim@xxxxxxxxxxx>
 Description:
 		 Controls the number of trials to find a victim segment.
 
+What:		/sys/fs/f2fs/<disk>/migration_granularity
+Date:		October 2018
+Contact:	"Chao Yu" <yuchao0@xxxxxxxxxx>
+Description:
+		 Controls migration granularity of garbage collection on large
+		 section, it can let GC move partial segment{s} of one section
+		 in one GC cycle, so that dispersing heavy overhead GC to
+		 multiple lightweight one.
+
 What:		/sys/fs/f2fs/<disk>/dir_level
 Date:		March 2014
 Contact:	"Jaegeuk Kim" <jaegeuk.kim@xxxxxxxxxxx>
diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
index 240e4881279e..b393fda6d6dc 100644
--- a/fs/f2fs/sysfs.c
+++ b/fs/f2fs/sysfs.c
@@ -246,6 +246,11 @@ static ssize_t __sbi_store(struct f2fs_attr *a,
 		return count;
 	}
 
+	if (!strcmp(a->attr.name, "discard_granularity")) {
+		if (t == 0 || t > sbi->segs_per_sec)
+			return -EINVAL;
+	}
+
 	if (!strcmp(a->attr.name, "trim_sections"))
 		return -EINVAL;
 
@@ -406,6 +411,7 @@ F2FS_RW_ATTR(NM_INFO, f2fs_nm_info, ram_thresh, ram_thresh);
 F2FS_RW_ATTR(NM_INFO, f2fs_nm_info, ra_nid_pages, ra_nid_pages);
 F2FS_RW_ATTR(NM_INFO, f2fs_nm_info, dirty_nats_ratio, dirty_nats_ratio);
 F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, max_victim_search, max_victim_search);
+F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, migration_granularity, migration_granularity);
 F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, dir_level, dir_level);
 F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, cp_interval, interval_time[CP_TIME]);
 F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, idle_interval, interval_time[REQ_TIME]);
@@ -460,6 +466,7 @@ static struct attribute *f2fs_attrs[] = {
 	ATTR_LIST(min_hot_blocks),
 	ATTR_LIST(min_ssr_sections),
 	ATTR_LIST(max_victim_search),
+	ATTR_LIST(migration_granularity),
 	ATTR_LIST(dir_level),
 	ATTR_LIST(ram_thresh),
 	ATTR_LIST(ra_nid_pages),
-- 
2.18.0.rc1