f2fs: change reclaim rate in percentage

It is more reasonable to determine the reclaiming rate of prefree segments
according to the volume size, which is set to 5% by default.
For example, if the volume is 128GB, the prefree segments are reclaimed
when the number reaches to 6.4GB.
Signed-off-by: NJaegeuk Kim <jaegeuk.kim@samsung.com>

Documentation/filesystems/f2fs.txt

@@ -169,9 +169,11 @@ Files in /sys/fs/f2fs/<devname>
 
  reclaim_segments             This parameter controls the number of prefree
                               segments to be reclaimed. If the number of prefree
-			      segments is larger than this number, f2fs tries to
-			      conduct checkpoint to reclaim the prefree segments
-			      to free segments. By default, 100 segments, 200MB.
+			      segments is larger than the number of segments
+			      in the proportion to the percentage over total
+			      volume size, f2fs tries to conduct checkpoint to
+			      reclaim the prefree segments to free segments.
+			      By default, 5% over total # of segments.
 
  max_small_discards	      This parameter controls the number of discard
 			      commands that consist small blocks less than 2MB.

fs/f2fs/segment.c

@@ -1758,7 +1758,8 @@ int build_segment_manager(struct f2fs_sb_info *sbi)
 	sm_info->ovp_segments = le32_to_cpu(ckpt->overprov_segment_count);
 	sm_info->main_segments = le32_to_cpu(raw_super->segment_count_main);
 	sm_info->ssa_blkaddr = le32_to_cpu(raw_super->ssa_blkaddr);
-	sm_info->rec_prefree_segments = DEF_RECLAIM_PREFREE_SEGMENTS;
+	sm_info->rec_prefree_segments = sm_info->main_segments *
+					DEF_RECLAIM_PREFREE_SEGMENTS / 100;
 	sm_info->ipu_policy = F2FS_IPU_DISABLE;
 	sm_info->min_ipu_util = DEF_MIN_IPU_UTIL;
 

fs/f2fs/segment.h

@@ -14,7 +14,7 @@
 #define NULL_SEGNO			((unsigned int)(~0))
 #define NULL_SECNO			((unsigned int)(~0))
 
-#define DEF_RECLAIM_PREFREE_SEGMENTS	100	/* 200MB of prefree segments */
+#define DEF_RECLAIM_PREFREE_SEGMENTS	5	/* 5% over total segments */
 
 /* L: Logical segment # in volume, R: Relative segment # in main area */
 #define GET_L2R_SEGNO(free_i, segno)	(segno - free_i->start_segno)