diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
index 7fd3511..3bbeca1 100644
--- a/fs/f2fs/segment.h
+++ b/fs/f2fs/segment.h
@@ -136,10 +136,12 @@
 /*
  * BG_GC means the background cleaning job.
  * FG_GC means the on-demand cleaning job.
+ * FORCE_FG_GC means on-demand cleaning job in background.
  */
 enum {
 	BG_GC = 0,
-	FG_GC
+	FG_GC,
+	FORCE_FG_GC,
 };
 
 /* for a function parameter to select a victim segment */
@@ -163,6 +165,7 @@
 	 */
 	unsigned short ckpt_valid_blocks;
 	unsigned char *ckpt_valid_map;
+	unsigned char *discard_map;
 	unsigned char type;		/* segment type like CURSEG_XXX_TYPE */
 	unsigned long long mtime;	/* modification time of the segment */
 };
@@ -175,6 +178,15 @@
 	void (*allocate_segment)(struct f2fs_sb_info *, int, bool);
 };
 
+/*
+ * this value is set in page as a private data which indicate that
+ * the page is atomically written, and it is in inmem_pages list.
+ */
+#define ATOMIC_WRITTEN_PAGE		0x0000ffff
+
+#define IS_ATOMIC_WRITTEN_PAGE(page)			\
+		(page_private(page) == (unsigned long)ATOMIC_WRITTEN_PAGE)
+
 struct inmem_pages {
 	struct list_head list;
 	struct page *page;
@@ -336,7 +348,8 @@
 	clear_bit(segno, free_i->free_segmap);
 	free_i->free_segments++;
 
-	next = find_next_bit(free_i->free_segmap, MAIN_SEGS(sbi), start_segno);
+	next = find_next_bit(free_i->free_segmap,
+			start_segno + sbi->segs_per_sec, start_segno);
 	if (next >= start_segno + sbi->segs_per_sec) {
 		clear_bit(secno, free_i->free_secmap);
 		free_i->free_sections++;
@@ -552,16 +565,15 @@
 	return curseg->next_blkoff;
 }
 
-#ifdef CONFIG_F2FS_CHECK_FS
 static inline void check_seg_range(struct f2fs_sb_info *sbi, unsigned int segno)
 {
-	BUG_ON(segno > TOTAL_SEGS(sbi) - 1);
+	f2fs_bug_on(sbi, segno > TOTAL_SEGS(sbi) - 1);
 }
 
 static inline void verify_block_addr(struct f2fs_sb_info *sbi, block_t blk_addr)
 {
-	BUG_ON(blk_addr < SEG0_BLKADDR(sbi));
-	BUG_ON(blk_addr >= MAX_BLKADDR(sbi));
+	f2fs_bug_on(sbi, blk_addr < SEG0_BLKADDR(sbi)
+					|| blk_addr >= MAX_BLKADDR(sbi));
 }
 
 /*
@@ -570,16 +582,11 @@
 static inline void check_block_count(struct f2fs_sb_info *sbi,
 		int segno, struct f2fs_sit_entry *raw_sit)
 {
+#ifdef CONFIG_F2FS_CHECK_FS
 	bool is_valid  = test_bit_le(0, raw_sit->valid_map) ? true : false;
 	int valid_blocks = 0;
 	int cur_pos = 0, next_pos;
 
-	/* check segment usage */
-	BUG_ON(GET_SIT_VBLOCKS(raw_sit) > sbi->blocks_per_seg);
-
-	/* check boundary of a given segment number */
-	BUG_ON(segno > TOTAL_SEGS(sbi) - 1);
-
 	/* check bitmap with valid block count */
 	do {
 		if (is_valid) {
@@ -595,35 +602,11 @@
 		is_valid = !is_valid;
 	} while (cur_pos < sbi->blocks_per_seg);
 	BUG_ON(GET_SIT_VBLOCKS(raw_sit) != valid_blocks);
-}
-#else
-static inline void check_seg_range(struct f2fs_sb_info *sbi, unsigned int segno)
-{
-	if (segno > TOTAL_SEGS(sbi) - 1)
-		set_sbi_flag(sbi, SBI_NEED_FSCK);
-}
-
-static inline void verify_block_addr(struct f2fs_sb_info *sbi, block_t blk_addr)
-{
-	if (blk_addr < SEG0_BLKADDR(sbi) || blk_addr >= MAX_BLKADDR(sbi))
-		set_sbi_flag(sbi, SBI_NEED_FSCK);
-}
-
-/*
- * Summary block is always treated as an invalid block
- */
-static inline void check_block_count(struct f2fs_sb_info *sbi,
-		int segno, struct f2fs_sit_entry *raw_sit)
-{
-	/* check segment usage */
-	if (GET_SIT_VBLOCKS(raw_sit) > sbi->blocks_per_seg)
-		set_sbi_flag(sbi, SBI_NEED_FSCK);
-
-	/* check boundary of a given segment number */
-	if (segno > TOTAL_SEGS(sbi) - 1)
-		set_sbi_flag(sbi, SBI_NEED_FSCK);
-}
 #endif
+	/* check segment usage, and check boundary of a given segment number */
+	f2fs_bug_on(sbi, GET_SIT_VBLOCKS(raw_sit) > sbi->blocks_per_seg
+					|| segno > TOTAL_SEGS(sbi) - 1);
+}
 
 static inline pgoff_t current_sit_addr(struct f2fs_sb_info *sbi,
 						unsigned int start)