diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
new file mode 100644
index 000000000000..46774ce3ae03
--- /dev/null
+++ b/fs/f2fs/gc.c
@@ -0,0 +1,742 @@
+/**
+ * fs/f2fs/gc.c
+ *
+ * Copyright (c) 2012 Samsung Electronics Co., Ltd.
+ *             http://www.samsung.com/
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+#include <linux/fs.h>
+#include <linux/module.h>
+#include <linux/backing-dev.h>
+#include <linux/proc_fs.h>
+#include <linux/init.h>
+#include <linux/f2fs_fs.h>
+#include <linux/kthread.h>
+#include <linux/delay.h>
+#include <linux/freezer.h>
+#include <linux/blkdev.h>
+
+#include "f2fs.h"
+#include "node.h"
+#include "segment.h"
+#include "gc.h"
+
+static struct kmem_cache *winode_slab;
+
+static int gc_thread_func(void *data)
+{
+	struct f2fs_sb_info *sbi = data;
+	wait_queue_head_t *wq = &sbi->gc_thread->gc_wait_queue_head;
+	long wait_ms;
+
+	wait_ms = GC_THREAD_MIN_SLEEP_TIME;
+
+	do {
+		if (try_to_freeze())
+			continue;
+		else
+			wait_event_interruptible_timeout(*wq,
+						kthread_should_stop(),
+						msecs_to_jiffies(wait_ms));
+		if (kthread_should_stop())
+			break;
+
+		f2fs_balance_fs(sbi);
+
+		if (!test_opt(sbi, BG_GC))
+			continue;
+
+		/*
+		 * [GC triggering condition]
+		 * 0. GC is not conducted currently.
+		 * 1. There are enough dirty segments.
+		 * 2. IO subsystem is idle by checking the # of writeback pages.
+		 * 3. IO subsystem is idle by checking the # of requests in
+		 *    bdev's request list.
+		 *
+		 * Note) We have to avoid triggering GCs too much frequently.
+		 * Because it is possible that some segments can be
+		 * invalidated soon after by user update or deletion.
+		 * So, I'd like to wait some time to collect dirty segments.
+		 */
+		if (!mutex_trylock(&sbi->gc_mutex))
+			continue;
+
+		if (!is_idle(sbi)) {
+			wait_ms = increase_sleep_time(wait_ms);
+			mutex_unlock(&sbi->gc_mutex);
+			continue;
+		}
+
+		if (has_enough_invalid_blocks(sbi))
+			wait_ms = decrease_sleep_time(wait_ms);
+		else
+			wait_ms = increase_sleep_time(wait_ms);
+
+		sbi->bg_gc++;
+
+		if (f2fs_gc(sbi, 1) == GC_NONE)
+			wait_ms = GC_THREAD_NOGC_SLEEP_TIME;
+		else if (wait_ms == GC_THREAD_NOGC_SLEEP_TIME)
+			wait_ms = GC_THREAD_MAX_SLEEP_TIME;
+
+	} while (!kthread_should_stop());
+	return 0;
+}
+
+int start_gc_thread(struct f2fs_sb_info *sbi)
+{
+	struct f2fs_gc_kthread *gc_th = NULL;
+
+	gc_th = kmalloc(sizeof(struct f2fs_gc_kthread), GFP_KERNEL);
+	if (!gc_th)
+		return -ENOMEM;
+
+	sbi->gc_thread = gc_th;
+	init_waitqueue_head(&sbi->gc_thread->gc_wait_queue_head);
+	sbi->gc_thread->f2fs_gc_task = kthread_run(gc_thread_func, sbi,
+				GC_THREAD_NAME);
+	if (IS_ERR(gc_th->f2fs_gc_task)) {
+		kfree(gc_th);
+		return -ENOMEM;
+	}
+	return 0;
+}
+
+void stop_gc_thread(struct f2fs_sb_info *sbi)
+{
+	struct f2fs_gc_kthread *gc_th = sbi->gc_thread;
+	if (!gc_th)
+		return;
+	kthread_stop(gc_th->f2fs_gc_task);
+	kfree(gc_th);
+	sbi->gc_thread = NULL;
+}
+
+static int select_gc_type(int gc_type)
+{
+	return (gc_type == BG_GC) ? GC_CB : GC_GREEDY;
+}
+
+static void select_policy(struct f2fs_sb_info *sbi, int gc_type,
+			int type, struct victim_sel_policy *p)
+{
+	struct dirty_seglist_info *dirty_i = DIRTY_I(sbi);
+
+	if (p->alloc_mode) {
+		p->gc_mode = GC_GREEDY;
+		p->dirty_segmap = dirty_i->dirty_segmap[type];
+		p->ofs_unit = 1;
+	} else {
+		p->gc_mode = select_gc_type(gc_type);
+		p->dirty_segmap = dirty_i->dirty_segmap[DIRTY];
+		p->ofs_unit = sbi->segs_per_sec;
+	}
+	p->offset = sbi->last_victim[p->gc_mode];
+}
+
+static unsigned int get_max_cost(struct f2fs_sb_info *sbi,
+				struct victim_sel_policy *p)
+{
+	if (p->gc_mode == GC_GREEDY)
+		return (1 << sbi->log_blocks_per_seg) * p->ofs_unit;
+	else if (p->gc_mode == GC_CB)
+		return UINT_MAX;
+	else /* No other gc_mode */
+		return 0;
+}
+
+static unsigned int check_bg_victims(struct f2fs_sb_info *sbi)
+{
+	struct dirty_seglist_info *dirty_i = DIRTY_I(sbi);
+	unsigned int segno;
+
+	/*
+	 * If the gc_type is FG_GC, we can select victim segments
+	 * selected by background GC before.
+	 * Those segments guarantee they have small valid blocks.
+	 */
+	segno = find_next_bit(dirty_i->victim_segmap[BG_GC],
+						TOTAL_SEGS(sbi), 0);
+	if (segno < TOTAL_SEGS(sbi)) {
+		clear_bit(segno, dirty_i->victim_segmap[BG_GC]);
+		return segno;
+	}
+	return NULL_SEGNO;
+}
+
+static unsigned int get_cb_cost(struct f2fs_sb_info *sbi, unsigned int segno)
+{
+	struct sit_info *sit_i = SIT_I(sbi);
+	unsigned int secno = GET_SECNO(sbi, segno);
+	unsigned int start = secno * sbi->segs_per_sec;
+	unsigned long long mtime = 0;
+	unsigned int vblocks;
+	unsigned char age = 0;
+	unsigned char u;
+	unsigned int i;
+
+	for (i = 0; i < sbi->segs_per_sec; i++)
+		mtime += get_seg_entry(sbi, start + i)->mtime;
+	vblocks = get_valid_blocks(sbi, segno, sbi->segs_per_sec);
+
+	mtime = div_u64(mtime, sbi->segs_per_sec);
+	vblocks = div_u64(vblocks, sbi->segs_per_sec);
+
+	u = (vblocks * 100) >> sbi->log_blocks_per_seg;
+
+	/* Handle if the system time is changed by user */
+	if (mtime < sit_i->min_mtime)
+		sit_i->min_mtime = mtime;
+	if (mtime > sit_i->max_mtime)
+		sit_i->max_mtime = mtime;
+	if (sit_i->max_mtime != sit_i->min_mtime)
+		age = 100 - div64_u64(100 * (mtime - sit_i->min_mtime),
+				sit_i->max_mtime - sit_i->min_mtime);
+
+	return UINT_MAX - ((100 * (100 - u) * age) / (100 + u));
+}
+
+static unsigned int get_gc_cost(struct f2fs_sb_info *sbi, unsigned int segno,
+					struct victim_sel_policy *p)
+{
+	if (p->alloc_mode == SSR)
+		return get_seg_entry(sbi, segno)->ckpt_valid_blocks;
+
+	/* alloc_mode == LFS */
+	if (p->gc_mode == GC_GREEDY)
+		return get_valid_blocks(sbi, segno, sbi->segs_per_sec);
+	else
+		return get_cb_cost(sbi, segno);
+}
+
+/**
+ * This function is called from two pathes.
+ * One is garbage collection and the other is SSR segment selection.
+ * When it is called during GC, it just gets a victim segment
+ * and it does not remove it from dirty seglist.
+ * When it is called from SSR segment selection, it finds a segment
+ * which has minimum valid blocks and removes it from dirty seglist.
+ */
+static int get_victim_by_default(struct f2fs_sb_info *sbi,
+		unsigned int *result, int gc_type, int type, char alloc_mode)
+{
+	struct dirty_seglist_info *dirty_i = DIRTY_I(sbi);
+	struct victim_sel_policy p;
+	unsigned int segno;
+	int nsearched = 0;
+
+	p.alloc_mode = alloc_mode;
+	select_policy(sbi, gc_type, type, &p);
+
+	p.min_segno = NULL_SEGNO;
+	p.min_cost = get_max_cost(sbi, &p);
+
+	mutex_lock(&dirty_i->seglist_lock);
+
+	if (p.alloc_mode == LFS && gc_type == FG_GC) {
+		p.min_segno = check_bg_victims(sbi);
+		if (p.min_segno != NULL_SEGNO)
+			goto got_it;
+	}
+
+	while (1) {
+		unsigned long cost;
+
+		segno = find_next_bit(p.dirty_segmap,
+						TOTAL_SEGS(sbi), p.offset);
+		if (segno >= TOTAL_SEGS(sbi)) {
+			if (sbi->last_victim[p.gc_mode]) {
+				sbi->last_victim[p.gc_mode] = 0;
+				p.offset = 0;
+				continue;
+			}
+			break;
+		}
+		p.offset = ((segno / p.ofs_unit) * p.ofs_unit) + p.ofs_unit;
+
+		if (test_bit(segno, dirty_i->victim_segmap[FG_GC]))
+			continue;
+		if (gc_type == BG_GC &&
+				test_bit(segno, dirty_i->victim_segmap[BG_GC]))
+			continue;
+		if (IS_CURSEC(sbi, GET_SECNO(sbi, segno)))
+			continue;
+
+		cost = get_gc_cost(sbi, segno, &p);
+
+		if (p.min_cost > cost) {
+			p.min_segno = segno;
+			p.min_cost = cost;
+		}
+
+		if (cost == get_max_cost(sbi, &p))
+			continue;
+
+		if (nsearched++ >= MAX_VICTIM_SEARCH) {
+			sbi->last_victim[p.gc_mode] = segno;
+			break;
+		}
+	}
+got_it:
+	if (p.min_segno != NULL_SEGNO) {
+		*result = (p.min_segno / p.ofs_unit) * p.ofs_unit;
+		if (p.alloc_mode == LFS) {
+			int i;
+			for (i = 0; i < p.ofs_unit; i++)
+				set_bit(*result + i,
+					dirty_i->victim_segmap[gc_type]);
+		}
+	}
+	mutex_unlock(&dirty_i->seglist_lock);
+
+	return (p.min_segno == NULL_SEGNO) ? 0 : 1;
+}
+
+static const struct victim_selection default_v_ops = {
+	.get_victim = get_victim_by_default,
+};
+
+static struct inode *find_gc_inode(nid_t ino, struct list_head *ilist)
+{
+	struct list_head *this;
+	struct inode_entry *ie;
+
+	list_for_each(this, ilist) {
+		ie = list_entry(this, struct inode_entry, list);
+		if (ie->inode->i_ino == ino)
+			return ie->inode;
+	}
+	return NULL;
+}
+
+static void add_gc_inode(struct inode *inode, struct list_head *ilist)
+{
+	struct list_head *this;
+	struct inode_entry *new_ie, *ie;
+
+	list_for_each(this, ilist) {
+		ie = list_entry(this, struct inode_entry, list);
+		if (ie->inode == inode) {
+			iput(inode);
+			return;
+		}
+	}
+repeat:
+	new_ie = kmem_cache_alloc(winode_slab, GFP_NOFS);
+	if (!new_ie) {
+		cond_resched();
+		goto repeat;
+	}
+	new_ie->inode = inode;
+	list_add_tail(&new_ie->list, ilist);
+}
+
+static void put_gc_inode(struct list_head *ilist)
+{
+	struct inode_entry *ie, *next_ie;
+	list_for_each_entry_safe(ie, next_ie, ilist, list) {
+		iput(ie->inode);
+		list_del(&ie->list);
+		kmem_cache_free(winode_slab, ie);
+	}
+}
+
+static int check_valid_map(struct f2fs_sb_info *sbi,
+				unsigned int segno, int offset)
+{
+	struct sit_info *sit_i = SIT_I(sbi);
+	struct seg_entry *sentry;
+	int ret;
+
+	mutex_lock(&sit_i->sentry_lock);
+	sentry = get_seg_entry(sbi, segno);
+	ret = f2fs_test_bit(offset, sentry->cur_valid_map);
+	mutex_unlock(&sit_i->sentry_lock);
+	return ret ? GC_OK : GC_NEXT;
+}
+
+/**
+ * This function compares node address got in summary with that in NAT.
+ * On validity, copy that node with cold status, otherwise (invalid node)
+ * ignore that.
+ */
+static int gc_node_segment(struct f2fs_sb_info *sbi,
+		struct f2fs_summary *sum, unsigned int segno, int gc_type)
+{
+	bool initial = true;
+	struct f2fs_summary *entry;
+	int off;
+
+next_step:
+	entry = sum;
+	for (off = 0; off < sbi->blocks_per_seg; off++, entry++) {
+		nid_t nid = le32_to_cpu(entry->nid);
+		struct page *node_page;
+		int err;
+
+		/*
+		 * It makes sure that free segments are able to write
+		 * all the dirty node pages before CP after this CP.
+		 * So let's check the space of dirty node pages.
+		 */
+		if (should_do_checkpoint(sbi)) {
+			mutex_lock(&sbi->cp_mutex);
+			block_operations(sbi);
+			return GC_BLOCKED;
+		}
+
+		err = check_valid_map(sbi, segno, off);
+		if (err == GC_ERROR)
+			return err;
+		else if (err == GC_NEXT)
+			continue;
+
+		if (initial) {
+			ra_node_page(sbi, nid);
+			continue;
+		}
+		node_page = get_node_page(sbi, nid);
+		if (IS_ERR(node_page))
+			continue;
+
+		/* set page dirty and write it */
+		if (!PageWriteback(node_page))
+			set_page_dirty(node_page);
+		f2fs_put_page(node_page, 1);
+		stat_inc_node_blk_count(sbi, 1);
+	}
+	if (initial) {
+		initial = false;
+		goto next_step;
+	}
+
+	if (gc_type == FG_GC) {
+		struct writeback_control wbc = {
+			.sync_mode = WB_SYNC_ALL,
+			.nr_to_write = LONG_MAX,
+			.for_reclaim = 0,
+		};
+		sync_node_pages(sbi, 0, &wbc);
+	}
+	return GC_DONE;
+}
+
+/**
+ * Calculate start block index that this node page contains
+ */
+block_t start_bidx_of_node(unsigned int node_ofs)
+{
+	block_t start_bidx;
+	unsigned int bidx, indirect_blks;
+	int dec;
+
+	indirect_blks = 2 * NIDS_PER_BLOCK + 4;
+
+	start_bidx = 1;
+	if (node_ofs == 0) {
+		start_bidx = 0;
+	} else if (node_ofs <= 2) {
+		bidx = node_ofs - 1;
+	} else if (node_ofs <= indirect_blks) {
+		dec = (node_ofs - 4) / (NIDS_PER_BLOCK + 1);
+		bidx = node_ofs - 2 - dec;
+	} else {
+		dec = (node_ofs - indirect_blks - 3) / (NIDS_PER_BLOCK + 1);
+		bidx = node_ofs - 5 - dec;
+	}
+
+	if (start_bidx)
+		start_bidx = bidx * ADDRS_PER_BLOCK + ADDRS_PER_INODE;
+	return start_bidx;
+}
+
+static int check_dnode(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
+		struct node_info *dni, block_t blkaddr, unsigned int *nofs)
+{
+	struct page *node_page;
+	nid_t nid;
+	unsigned int ofs_in_node;
+	block_t source_blkaddr;
+
+	nid = le32_to_cpu(sum->nid);
+	ofs_in_node = le16_to_cpu(sum->ofs_in_node);
+
+	node_page = get_node_page(sbi, nid);
+	if (IS_ERR(node_page))
+		return GC_NEXT;
+
+	get_node_info(sbi, nid, dni);
+
+	if (sum->version != dni->version) {
+		f2fs_put_page(node_page, 1);
+		return GC_NEXT;
+	}
+
+	*nofs = ofs_of_node(node_page);
+	source_blkaddr = datablock_addr(node_page, ofs_in_node);
+	f2fs_put_page(node_page, 1);
+
+	if (source_blkaddr != blkaddr)
+		return GC_NEXT;
+	return GC_OK;
+}
+
+static void move_data_page(struct inode *inode, struct page *page, int gc_type)
+{
+	if (page->mapping != inode->i_mapping)
+		goto out;
+
+	if (inode != page->mapping->host)
+		goto out;
+
+	if (PageWriteback(page))
+		goto out;
+
+	if (gc_type == BG_GC) {
+		set_page_dirty(page);
+		set_cold_data(page);
+	} else {
+		struct f2fs_sb_info *sbi = F2FS_SB(inode->i_sb);
+		mutex_lock_op(sbi, DATA_WRITE);
+		if (clear_page_dirty_for_io(page) &&
+			S_ISDIR(inode->i_mode)) {
+			dec_page_count(sbi, F2FS_DIRTY_DENTS);
+			inode_dec_dirty_dents(inode);
+		}
+		set_cold_data(page);
+		do_write_data_page(page);
+		mutex_unlock_op(sbi, DATA_WRITE);
+		clear_cold_data(page);
+	}
+out:
+	f2fs_put_page(page, 1);
+}
+
+/**
+ * This function tries to get parent node of victim data block, and identifies
+ * data block validity. If the block is valid, copy that with cold status and
+ * modify parent node.
+ * If the parent node is not valid or the data block address is different,
+ * the victim data block is ignored.
+ */
+static int gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
+		struct list_head *ilist, unsigned int segno, int gc_type)
+{
+	struct super_block *sb = sbi->sb;
+	struct f2fs_summary *entry;
+	block_t start_addr;
+	int err, off;
+	int phase = 0;
+
+	start_addr = START_BLOCK(sbi, segno);
+
+next_step:
+	entry = sum;
+	for (off = 0; off < sbi->blocks_per_seg; off++, entry++) {
+		struct page *data_page;
+		struct inode *inode;
+		struct node_info dni; /* dnode info for the data */
+		unsigned int ofs_in_node, nofs;
+		block_t start_bidx;
+
+		/*
+		 * It makes sure that free segments are able to write
+		 * all the dirty node pages before CP after this CP.
+		 * So let's check the space of dirty node pages.
+		 */
+		if (should_do_checkpoint(sbi)) {
+			mutex_lock(&sbi->cp_mutex);
+			block_operations(sbi);
+			err = GC_BLOCKED;
+			goto stop;
+		}
+
+		err = check_valid_map(sbi, segno, off);
+		if (err == GC_ERROR)
+			goto stop;
+		else if (err == GC_NEXT)
+			continue;
+
+		if (phase == 0) {
+			ra_node_page(sbi, le32_to_cpu(entry->nid));
+			continue;
+		}
+
+		/* Get an inode by ino with checking validity */
+		err = check_dnode(sbi, entry, &dni, start_addr + off, &nofs);
+		if (err == GC_ERROR)
+			goto stop;
+		else if (err == GC_NEXT)
+			continue;
+
+		if (phase == 1) {
+			ra_node_page(sbi, dni.ino);
+			continue;
+		}
+
+		start_bidx = start_bidx_of_node(nofs);
+		ofs_in_node = le16_to_cpu(entry->ofs_in_node);
+
+		if (phase == 2) {
+			inode = f2fs_iget_nowait(sb, dni.ino);
+			if (IS_ERR(inode))
+				continue;
+
+			data_page = find_data_page(inode,
+					start_bidx + ofs_in_node);
+			if (IS_ERR(data_page))
+				goto next_iput;
+
+			f2fs_put_page(data_page, 0);
+			add_gc_inode(inode, ilist);
+		} else {
+			inode = find_gc_inode(dni.ino, ilist);
+			if (inode) {
+				data_page = get_lock_data_page(inode,
+						start_bidx + ofs_in_node);
+				if (IS_ERR(data_page))
+					continue;
+				move_data_page(inode, data_page, gc_type);
+				stat_inc_data_blk_count(sbi, 1);
+			}
+		}
+		continue;
+next_iput:
+		iput(inode);
+	}
+	if (++phase < 4)
+		goto next_step;
+	err = GC_DONE;
+stop:
+	if (gc_type == FG_GC)
+		f2fs_submit_bio(sbi, DATA, true);
+	return err;
+}
+
+static int __get_victim(struct f2fs_sb_info *sbi, unsigned int *victim,
+						int gc_type, int type)
+{
+	struct sit_info *sit_i = SIT_I(sbi);
+	int ret;
+	mutex_lock(&sit_i->sentry_lock);
+	ret = DIRTY_I(sbi)->v_ops->get_victim(sbi, victim, gc_type, type, LFS);
+	mutex_unlock(&sit_i->sentry_lock);
+	return ret;
+}
+
+static int do_garbage_collect(struct f2fs_sb_info *sbi, unsigned int segno,
+				struct list_head *ilist, int gc_type)
+{
+	struct page *sum_page;
+	struct f2fs_summary_block *sum;
+	int ret = GC_DONE;
+
+	/* read segment summary of victim */
+	sum_page = get_sum_page(sbi, segno);
+	if (IS_ERR(sum_page))
+		return GC_ERROR;
+
+	/*
+	 * CP needs to lock sum_page. In this time, we don't need
+	 * to lock this page, because this summary page is not gone anywhere.
+	 * Also, this page is not gonna be updated before GC is done.
+	 */
+	unlock_page(sum_page);
+	sum = page_address(sum_page);
+
+	switch (GET_SUM_TYPE((&sum->footer))) {
+	case SUM_TYPE_NODE:
+		ret = gc_node_segment(sbi, sum->entries, segno, gc_type);
+		break;
+	case SUM_TYPE_DATA:
+		ret = gc_data_segment(sbi, sum->entries, ilist, segno, gc_type);
+		break;
+	}
+	stat_inc_seg_count(sbi, GET_SUM_TYPE((&sum->footer)));
+	stat_inc_call_count(sbi->stat_info);
+
+	f2fs_put_page(sum_page, 0);
+	return ret;
+}
+
+int f2fs_gc(struct f2fs_sb_info *sbi, int nGC)
+{
+	unsigned int segno;
+	int old_free_secs, cur_free_secs;
+	int gc_status, nfree;
+	struct list_head ilist;
+	int gc_type = BG_GC;
+
+	INIT_LIST_HEAD(&ilist);
+gc_more:
+	nfree = 0;
+	gc_status = GC_NONE;
+
+	if (has_not_enough_free_secs(sbi))
+		old_free_secs = reserved_sections(sbi);
+	else
+		old_free_secs = free_sections(sbi);
+
+	while (sbi->sb->s_flags & MS_ACTIVE) {
+		int i;
+		if (has_not_enough_free_secs(sbi))
+			gc_type = FG_GC;
+
+		cur_free_secs = free_sections(sbi) + nfree;
+
+		/* We got free space successfully. */
+		if (nGC < cur_free_secs - old_free_secs)
+			break;
+
+		if (!__get_victim(sbi, &segno, gc_type, NO_CHECK_TYPE))
+			break;
+
+		for (i = 0; i < sbi->segs_per_sec; i++) {
+			/*
+			 * do_garbage_collect will give us three gc_status:
+			 * GC_ERROR, GC_DONE, and GC_BLOCKED.
+			 * If GC is finished uncleanly, we have to return
+			 * the victim to dirty segment list.
+			 */
+			gc_status = do_garbage_collect(sbi, segno + i,
+					&ilist, gc_type);
+			if (gc_status != GC_DONE)
+				goto stop;
+			nfree++;
+		}
+	}
+stop:
+	if (has_not_enough_free_secs(sbi) || gc_status == GC_BLOCKED) {
+		write_checkpoint(sbi, (gc_status == GC_BLOCKED), false);
+		if (nfree)
+			goto gc_more;
+	}
+	mutex_unlock(&sbi->gc_mutex);
+
+	put_gc_inode(&ilist);
+	BUG_ON(!list_empty(&ilist));
+	return gc_status;
+}
+
+void build_gc_manager(struct f2fs_sb_info *sbi)
+{
+	DIRTY_I(sbi)->v_ops = &default_v_ops;
+}
+
+int create_gc_caches(void)
+{
+	winode_slab = f2fs_kmem_cache_create("f2fs_gc_inodes",
+			sizeof(struct inode_entry), NULL);
+	if (!winode_slab)
+		return -ENOMEM;
+	return 0;
+}
+
+void destroy_gc_caches(void)
+{
+	kmem_cache_destroy(winode_slab);
+}
diff --git a/fs/f2fs/gc.h b/fs/f2fs/gc.h
new file mode 100644
index 000000000000..cf42a554ca0a
--- /dev/null
+++ b/fs/f2fs/gc.h
@@ -0,0 +1,117 @@
+/**
+ * fs/f2fs/gc.h
+ *
+ * Copyright (c) 2012 Samsung Electronics Co., Ltd.
+ *             http://www.samsung.com/
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+#define GC_THREAD_NAME	"f2fs_gc_task"
+#define GC_THREAD_MIN_WB_PAGES		1	/*
+						 * a threshold to determine
+						 * whether IO subsystem is idle
+						 * or not
+						 */
+#define GC_THREAD_MIN_SLEEP_TIME	10000 /* milliseconds */
+#define GC_THREAD_MAX_SLEEP_TIME	30000
+#define GC_THREAD_NOGC_SLEEP_TIME	10000
+#define LIMIT_INVALID_BLOCK	40 /* percentage over total user space */
+#define LIMIT_FREE_BLOCK	40 /* percentage over invalid + free space */
+
+/* Search max. number of dirty segments to select a victim segment */
+#define MAX_VICTIM_SEARCH	20
+
+enum {
+	GC_NONE = 0,
+	GC_ERROR,
+	GC_OK,
+	GC_NEXT,
+	GC_BLOCKED,
+	GC_DONE,
+};
+
+struct f2fs_gc_kthread {
+	struct task_struct *f2fs_gc_task;
+	wait_queue_head_t gc_wait_queue_head;
+};
+
+struct inode_entry {
+	struct list_head list;
+	struct inode *inode;
+};
+
+/**
+ * inline functions
+ */
+static inline block_t free_user_blocks(struct f2fs_sb_info *sbi)
+{
+	if (free_segments(sbi) < overprovision_segments(sbi))
+		return 0;
+	else
+		return (free_segments(sbi) - overprovision_segments(sbi))
+			<< sbi->log_blocks_per_seg;
+}
+
+static inline block_t limit_invalid_user_blocks(struct f2fs_sb_info *sbi)
+{
+	return (long)(sbi->user_block_count * LIMIT_INVALID_BLOCK) / 100;
+}
+
+static inline block_t limit_free_user_blocks(struct f2fs_sb_info *sbi)
+{
+	block_t reclaimable_user_blocks = sbi->user_block_count -
+		written_block_count(sbi);
+	return (long)(reclaimable_user_blocks * LIMIT_FREE_BLOCK) / 100;
+}
+
+static inline long increase_sleep_time(long wait)
+{
+	wait += GC_THREAD_MIN_SLEEP_TIME;
+	if (wait > GC_THREAD_MAX_SLEEP_TIME)
+		wait = GC_THREAD_MAX_SLEEP_TIME;
+	return wait;
+}
+
+static inline long decrease_sleep_time(long wait)
+{
+	wait -= GC_THREAD_MIN_SLEEP_TIME;
+	if (wait <= GC_THREAD_MIN_SLEEP_TIME)
+		wait = GC_THREAD_MIN_SLEEP_TIME;
+	return wait;
+}
+
+static inline bool has_enough_invalid_blocks(struct f2fs_sb_info *sbi)
+{
+	block_t invalid_user_blocks = sbi->user_block_count -
+					written_block_count(sbi);
+	/*
+	 * Background GC is triggered with the following condition.
+	 * 1. There are a number of invalid blocks.
+	 * 2. There is not enough free space.
+	 */
+	if (invalid_user_blocks > limit_invalid_user_blocks(sbi) &&
+			free_user_blocks(sbi) < limit_free_user_blocks(sbi))
+		return true;
+	return false;
+}
+
+static inline int is_idle(struct f2fs_sb_info *sbi)
+{
+	struct block_device *bdev = sbi->sb->s_bdev;
+	struct request_queue *q = bdev_get_queue(bdev);
+	struct request_list *rl = &q->root_rl;
+	return !(rl->count[BLK_RW_SYNC]) && !(rl->count[BLK_RW_ASYNC]);
+}
+
+static inline bool should_do_checkpoint(struct f2fs_sb_info *sbi)
+{
+	unsigned int pages_per_sec = sbi->segs_per_sec *
+					(1 << sbi->log_blocks_per_seg);
+	int node_secs = ((get_pages(sbi, F2FS_DIRTY_NODES) + pages_per_sec - 1)
+			>> sbi->log_blocks_per_seg) / sbi->segs_per_sec;
+	int dent_secs = ((get_pages(sbi, F2FS_DIRTY_DENTS) + pages_per_sec - 1)
+			>> sbi->log_blocks_per_seg) / sbi->segs_per_sec;
+	return free_sections(sbi) <= (node_secs + 2 * dent_secs + 2);
+}