[PATCH v2 5/5] f2fs: support age threshold based garbage collection

[Chao Yu]

There are several issues in current background GC algorithm:
- valid blocks is one of key factors during cost overhead calculation,
so if segment has less valid block, however even its age is young or
it locates hot segment, CB algorithm will still choose the segment as
victim, it's not appropriate.
- GCed data/node will go to existing logs, no matter in-there datas'
update frequency is the same or not, it may mix hot and cold data
again.
- GC alloctor mainly use LFS type segment, it will cost free segment
more quickly.

This patch introduces a new algorithm named age threshold based
garbage collection to solve above issues, there are three steps
mainly:

1. select a source victim:
- set an age threshold, and select candidates beased threshold:
e.g.
 0 means youngest, 100 means oldest, if we set age threshold to 80
 then select dirty segments which has age in range of [80, 100] as
 candiddates;
- set candidate_ratio threshold, and select candidates based the
ratio, so that we can shrink candidates to those oldest segments;
- select target segment with fewest valid blocks in order to
migrate blocks with minimum cost;

2. select a target victim:
- select candidates beased age threshold;
- set candidate_radius threshold, search candidates whose age is
around source victims, searching radius should less than the
radius threshold.
- select target segment with most valid blocks in order to avoid
migrating current target segment.

3. merge valid blocks from source victim into target victim with
SSR alloctor.

Test steps:
- create 160 dirty segments:
 * half of them have 128 valid blocks per segment
 * left of them have 384 valid blocks per segment
- run background GC

Benefit: GC count and block movement count both decrease obviously:

- Before:
  - Valid: 86
  - Dirty: 1
  - Prefree: 11
  - Free: 6001 (6001)

GC calls: 162 (BG: 220)
  - data segments : 160 (160)
  - node segments : 2 (2)
Try to move 41454 blocks (BG: 41454)
  - data blocks : 40960 (40960)
  - node blocks : 494 (494)

IPU: 0 blocks
SSR: 0 blocks in 0 segments
LFS: 41364 blocks in 81 segments

- After:

  - Valid: 87
  - Dirty: 0
  - Prefree: 4
  - Free: 6008 (6008)

GC calls: 75 (BG: 76)
  - data segments : 74 (74)
  - node segments : 1 (1)
Try to move 12813 blocks (BG: 12813)
  - data blocks : 12544 (12544)
  - node blocks : 269 (269)

IPU: 0 blocks
SSR: 12032 blocks in 77 segments
LFS: 855 blocks in 2 segments

Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
---
 Documentation/filesystems/f2fs.rst |   2 +
 fs/f2fs/checkpoint.c               |   4 +-
 fs/f2fs/data.c                     |   2 +-
 fs/f2fs/debug.c                    |   4 +
 fs/f2fs/f2fs.h                     |  29 ++-
 fs/f2fs/gc.c                       | 368 ++++++++++++++++++++++++++++-
 fs/f2fs/gc.h                       |  25 ++
 fs/f2fs/segment.c                  | 182 +++++++++++---
 fs/f2fs/segment.h                  |  25 +-
 fs/f2fs/super.c                    |  26 +-
 include/trace/events/f2fs.h        |   8 +-
 11 files changed, 617 insertions(+), 58 deletions(-)

diff --git a/Documentation/filesystems/f2fs.rst b/Documentation/filesystems/f2fs.rst
index de43239a3c31..58c2549ee602 100644
--- a/Documentation/filesystems/f2fs.rst
+++ b/Documentation/filesystems/f2fs.rst
@@ -260,6 +260,8 @@ compress_extension=%s  Support adding specified extension, so that f2fs can enab
                        For other files, we can still enable compression via ioctl.
                        Note that, there is one reserved special extension '*', it
                        can be set to enable compression for all files.
+atgc                   Enable age-threshold garbage collection, it provides high
+                       effectiveness and efficiency on background GC.
 ====================== ============================================================
 
 Debugfs Entries
diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index 9e30ff6414b8..6059ce3758d8 100644
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -1620,7 +1620,7 @@ int f2fs_write_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
 	f2fs_flush_sit_entries(sbi, cpc);
 
 	/* save inmem log status */
-	f2fs_save_inmem_curseg(sbi, CURSEG_COLD_DATA_PINNED);
+	f2fs_save_inmem_curseg(sbi);
 
 	err = do_checkpoint(sbi, cpc);
 	if (err)
@@ -1628,7 +1628,7 @@ int f2fs_write_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
 	else
 		f2fs_clear_prefree_segments(sbi, cpc);
 
-	f2fs_restore_inmem_curseg(sbi, CURSEG_COLD_DATA_PINNED);
+	f2fs_restore_inmem_curseg(sbi);
 stop:
 	unblock_operations(sbi);
 	stat_inc_cp_count(sbi->stat_info);
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 2b2bfda756a8..1c3154914522 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -1368,7 +1368,7 @@ static int __allocate_data_block(struct dnode_of_data *dn, int seg_type)
 	set_summary(&sum, dn->nid, dn->ofs_in_node, ni.version);
 	old_blkaddr = dn->data_blkaddr;
 	f2fs_allocate_data_block(sbi, NULL, old_blkaddr, &dn->data_blkaddr,
-				&sum, seg_type, NULL, false);
+				&sum, seg_type, NULL);
 	if (GET_SEGNO(sbi, old_blkaddr) != NULL_SEGNO)
 		invalidate_mapping_pages(META_MAPPING(sbi),
 					old_blkaddr, old_blkaddr);
diff --git a/fs/f2fs/debug.c b/fs/f2fs/debug.c
index 41a91aa8c262..cb679561f44d 100644
--- a/fs/f2fs/debug.c
+++ b/fs/f2fs/debug.c
@@ -397,6 +397,10 @@ static int stat_show(struct seq_file *s, void *v)
 			   si->curseg[CURSEG_COLD_DATA_PINNED],
 			   si->cursec[CURSEG_COLD_DATA_PINNED],
 			   si->curzone[CURSEG_COLD_DATA_PINNED]);
+		seq_printf(s, "  - ATGC   data: %8d %8d %8d\n",
+			   si->curseg[CURSEG_ALL_DATA_ATGC],
+			   si->cursec[CURSEG_ALL_DATA_ATGC],
+			   si->curzone[CURSEG_ALL_DATA_ATGC]);
 		seq_printf(s, "\n  - Valid: %d\n  - Dirty: %d\n",
 			   si->main_area_segs - si->dirty_count -
 			   si->prefree_count - si->free_segs,
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 44445b9ccc1b..3b9c38d5bf58 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -98,6 +98,7 @@ extern const char *f2fs_fault_name[FAULT_MAX];
 #define F2FS_MOUNT_RESERVE_ROOT		0x01000000
 #define F2FS_MOUNT_DISABLE_CHECKPOINT	0x02000000
 #define F2FS_MOUNT_NORECOVERY		0x04000000
+#define F2FS_MOUNT_ATGC			0x08000000
 
 #define F2FS_OPTION(sbi)	((sbi)->mount_opt)
 #define clear_opt(sbi, option)	(F2FS_OPTION(sbi).opt &= ~F2FS_MOUNT_##option)
@@ -978,7 +979,7 @@ static inline void set_new_dnode(struct dnode_of_data *dn, struct inode *inode,
  */
 #define	NR_CURSEG_DATA_TYPE	(3)
 #define NR_CURSEG_NODE_TYPE	(3)
-#define NR_CURSEG_INMEM_TYPE	(1)
+#define NR_CURSEG_INMEM_TYPE	(2)
 #define NR_CURSEG_PERSIST_TYPE	(NR_CURSEG_DATA_TYPE + NR_CURSEG_NODE_TYPE)
 #define NR_CURSEG_TYPE		(NR_CURSEG_INMEM_TYPE + NR_CURSEG_PERSIST_TYPE)
 
@@ -992,6 +993,7 @@ enum {
 	NR_PERSISTENT_LOG,	/* number of persistent log */
 	CURSEG_COLD_DATA_PINNED = NR_PERSISTENT_LOG,
 				/* pinned file that needs consecutive block address */
+	CURSEG_ALL_DATA_ATGC,	/* SSR alloctor in hot/warm/cold data area */
 	NO_CHECK_TYPE,		/* number of persistent & inmem log */
 };
 
@@ -1237,6 +1239,18 @@ struct inode_management {
 	unsigned long ino_num;			/* number of entries */
 };
 
+/* for GC_AT */
+struct atgc_management {
+	bool atgc_enabled;			/* ATGC is enabled or not */
+	struct rb_root_cached root;		/* root of victim rb-tree */
+	struct list_head victim_list;		/* linked with all victim entries */
+	unsigned int victim_count;		/* victim count in rb-tree */
+	unsigned int candidate_ratio;		/* candidate ratio */
+	unsigned int max_candidate_count;	/* max candidate count */
+	unsigned int age_weight;		/* age weight, vblock_weight = 100 - age_weight */
+	unsigned long long age_threshold;	/* age threshold */
+};
+
 /* For s_flag in struct f2fs_sb_info */
 enum {
 	SBI_IS_DIRTY,				/* dirty flag for checkpoint */
@@ -1269,6 +1283,7 @@ enum {
 	GC_NORMAL,
 	GC_IDLE_CB,
 	GC_IDLE_GREEDY,
+	GC_IDLE_AT,
 	GC_URGENT_HIGH,
 	GC_URGENT_LOW,
 };
@@ -1524,6 +1539,7 @@ struct f2fs_sb_info {
 						 * race between GC and GC or CP
 						 */
 	struct f2fs_gc_kthread	*gc_thread;	/* GC thread */
+	struct atgc_management am;		/* atgc management */
 	unsigned int cur_victim_sec;		/* current victim section num */
 	unsigned int gc_mode;			/* current GC state */
 	unsigned int next_victim_seg[2];	/* next segment in victim section */
@@ -3341,8 +3357,11 @@ block_t f2fs_get_unusable_blocks(struct f2fs_sb_info *sbi);
 int f2fs_disable_cp_again(struct f2fs_sb_info *sbi, block_t unusable);
 void f2fs_release_discard_addrs(struct f2fs_sb_info *sbi);
 int f2fs_npages_for_summary_flush(struct f2fs_sb_info *sbi, bool for_ra);
-void f2fs_save_inmem_curseg(struct f2fs_sb_info *sbi, int type);
-void f2fs_restore_inmem_curseg(struct f2fs_sb_info *sbi, int type);
+void f2fs_init_inmem_curseg(struct f2fs_sb_info *sbi);
+void f2fs_save_inmem_curseg(struct f2fs_sb_info *sbi);
+void f2fs_restore_inmem_curseg(struct f2fs_sb_info *sbi);
+void f2fs_get_new_segment(struct f2fs_sb_info *sbi,
+			unsigned int *newseg, bool new_sec, int dir);
 void f2fs_allocate_segment_for_resize(struct f2fs_sb_info *sbi, int type,
 					unsigned int start, unsigned int end);
 void f2fs_allocate_new_segment(struct f2fs_sb_info *sbi, int type);
@@ -3370,7 +3389,7 @@ void f2fs_replace_block(struct f2fs_sb_info *sbi, struct dnode_of_data *dn,
 void f2fs_allocate_data_block(struct f2fs_sb_info *sbi, struct page *page,
 			block_t old_blkaddr, block_t *new_blkaddr,
 			struct f2fs_summary *sum, int type,
-			struct f2fs_io_info *fio, bool from_gc);
+			struct f2fs_io_info *fio);
 void f2fs_wait_on_page_writeback(struct page *page,
 			enum page_type type, bool ordered, bool locked);
 void f2fs_wait_on_block_writeback(struct inode *inode, block_t blkaddr);
@@ -3505,6 +3524,8 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync, bool background,
 			unsigned int segno);
 void f2fs_build_gc_manager(struct f2fs_sb_info *sbi);
 int f2fs_resize_fs(struct f2fs_sb_info *sbi, __u64 block_count);
+int __init f2fs_create_garbage_collection_cache(void);
+void f2fs_destroy_garbage_collection_cache(void);
 
 /*
  * recovery.c
diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index da187aec988f..a38d41b21019 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -21,6 +21,8 @@
 #include "gc.h"
 #include <trace/events/f2fs.h>
 
+static struct kmem_cache *victim_entry_slab;
+
 static unsigned int count_bits(const unsigned long *addr,
 				unsigned int offset, unsigned int len);
 
@@ -169,7 +171,16 @@ void f2fs_stop_gc_thread(struct f2fs_sb_info *sbi)
 
 static int select_gc_type(struct f2fs_sb_info *sbi, int gc_type)
 {
-	int gc_mode = (gc_type == BG_GC) ? GC_CB : GC_GREEDY;
+	int gc_mode;
+
+	if (gc_type == BG_GC) {
+		if (sbi->am.atgc_enabled)
+			gc_mode = GC_AT;
+		else
+			gc_mode = GC_CB;
+	} else {
+		gc_mode = GC_GREEDY;
+	}
 
 	switch (sbi->gc_mode) {
 	case GC_IDLE_CB:
@@ -179,7 +190,11 @@ static int select_gc_type(struct f2fs_sb_info *sbi, int gc_type)
 	case GC_URGENT_HIGH:
 		gc_mode = GC_GREEDY;
 		break;
+	case GC_IDLE_AT:
+		gc_mode = GC_AT;
+		break;
 	}
+
 	return gc_mode;
 }
 
@@ -193,6 +208,11 @@ static void select_policy(struct f2fs_sb_info *sbi, int gc_type,
 		p->dirty_bitmap = dirty_i->dirty_segmap[type];
 		p->max_search = dirty_i->nr_dirty[type];
 		p->ofs_unit = 1;
+	} else if (p->alloc_mode == AT_SSR) {
+		p->gc_mode = GC_GREEDY;
+		p->dirty_bitmap = dirty_i->dirty_segmap[type];
+		p->max_search = dirty_i->nr_dirty[type];
+		p->ofs_unit = 1;
 	} else {
 		p->gc_mode = select_gc_type(sbi, gc_type);
 		p->ofs_unit = sbi->segs_per_sec;
@@ -212,6 +232,7 @@ static void select_policy(struct f2fs_sb_info *sbi, int gc_type,
 	 */
 	if (gc_type != FG_GC &&
 			(sbi->gc_mode != GC_URGENT_HIGH) &&
+			(p->gc_mode != GC_AT && p->alloc_mode != AT_SSR) &&
 			p->max_search > sbi->max_victim_search)
 		p->max_search = sbi->max_victim_search;
 
@@ -229,10 +250,16 @@ static unsigned int get_max_cost(struct f2fs_sb_info *sbi,
 	/* SSR allocates in a segment unit */
 	if (p->alloc_mode == SSR)
 		return sbi->blocks_per_seg;
+	else if (p->alloc_mode == AT_SSR)
+		return UINT_MAX;
+
+	/* LFS */
 	if (p->gc_mode == GC_GREEDY)
 		return 2 * sbi->blocks_per_seg * p->ofs_unit;
 	else if (p->gc_mode == GC_CB)
 		return UINT_MAX;
+	else if (p->gc_mode == GC_AT)
+		return UINT_MAX;
 	else /* No other gc_mode */
 		return 0;
 }
@@ -297,8 +324,11 @@ static inline unsigned int get_gc_cost(struct f2fs_sb_info *sbi,
 	/* alloc_mode == LFS */
 	if (p->gc_mode == GC_GREEDY)
 		return get_valid_blocks(sbi, segno, true);
-	else
+	else if (p->gc_mode == GC_CB)
 		return get_cb_cost(sbi, segno);
+
+	f2fs_bug_on(sbi, 1);
+	return 0;
 }
 
 static unsigned int count_bits(const unsigned long *addr,
@@ -313,6 +343,263 @@ static unsigned int count_bits(const unsigned long *addr,
 	return sum;
 }
 
+static struct victim_entry *attach_victim_entry(struct f2fs_sb_info *sbi,
+				unsigned long long mtime, unsigned int segno,
+				struct rb_node *parent, struct rb_node **p,
+				bool left_most)
+{
+	struct atgc_management *am = &sbi->am;
+	struct victim_entry *ve;
+
+	ve =  f2fs_kmem_cache_alloc(victim_entry_slab, GFP_NOFS);
+
+	ve->mtime = mtime;
+	ve->segno = segno;
+
+	rb_link_node(&ve->rb_node, parent, p);
+	rb_insert_color_cached(&ve->rb_node, &am->root, left_most);
+
+	list_add_tail(&ve->list, &am->victim_list);
+
+	am->victim_count++;
+
+	return ve;
+}
+
+static void insert_victim_entry(struct f2fs_sb_info *sbi,
+				unsigned long long mtime, unsigned int segno)
+{
+	struct atgc_management *am = &sbi->am;
+	struct rb_node **p;
+	struct rb_node *parent = NULL;
+	bool left_most = true;
+
+	p = f2fs_lookup_rb_tree_ext(sbi, &am->root, &parent, mtime, &left_most);
+	attach_victim_entry(sbi, mtime, segno, parent, p, left_most);
+}
+
+static void add_victim_entry(struct f2fs_sb_info *sbi,
+				struct victim_sel_policy *p, unsigned int segno)
+{
+	struct sit_info *sit_i = SIT_I(sbi);
+	unsigned int secno = GET_SEC_FROM_SEG(sbi, segno);
+	unsigned int start = GET_SEG_FROM_SEC(sbi, secno);
+	unsigned long long mtime = 0;
+	unsigned int i;
+
+	for (i = 0; i < sbi->segs_per_sec; i++)
+		mtime += get_seg_entry(sbi, start + i)->mtime;
+	mtime = div_u64(mtime, sbi->segs_per_sec);
+
+	/* Handle if the system time has changed by the user */
+	if (mtime < sit_i->min_mtime)
+		sit_i->min_mtime = mtime;
+	if (mtime > sit_i->max_mtime)
+		sit_i->max_mtime = mtime;
+	if (mtime < sit_i->dirty_min_mtime)
+		sit_i->dirty_min_mtime = mtime;
+	if (mtime > sit_i->dirty_max_mtime)
+		sit_i->dirty_max_mtime = mtime;
+
+	/* don't choose young section as candidate */
+	if (sit_i->dirty_max_mtime - mtime < p->age_threshold)
+		return;
+
+	insert_victim_entry(sbi, mtime, segno);
+}
+
+static struct rb_node *lookup_central_victim(struct f2fs_sb_info *sbi,
+						struct victim_sel_policy *p)
+{
+	struct atgc_management *am = &sbi->am;
+	struct rb_node *parent = NULL;
+	bool left_most;
+
+	f2fs_lookup_rb_tree_ext(sbi, &am->root, &parent, p->age, &left_most);
+
+	return parent;
+}
+
+static void atgc_lookup_victim(struct f2fs_sb_info *sbi,
+						struct victim_sel_policy *p)
+{
+	struct sit_info *sit_i = SIT_I(sbi);
+	struct atgc_management *am = &sbi->am;
+	struct rb_root_cached *root = &am->root;
+	struct rb_node *node;
+	struct rb_entry *re;
+	struct victim_entry *ve;
+	unsigned long long total_time;
+	unsigned long long age, u, accu;
+	unsigned long long max_mtime = sit_i->dirty_max_mtime;
+	unsigned long long min_mtime = sit_i->dirty_min_mtime;
+	unsigned int sec_blocks = BLKS_PER_SEC(sbi);
+	unsigned int vblocks;
+	unsigned int dirty_threshold = max(am->max_candidate_count,
+					am->candidate_ratio *
+					am->victim_count / 100);
+	unsigned int age_weight = am->age_weight;
+	unsigned int cost;
+	unsigned int iter = 0;
+
+	if (max_mtime < min_mtime)
+		return;
+
+	max_mtime += 1;
+	total_time = max_mtime - min_mtime;
+
+	accu = div64_u64(ULLONG_MAX, total_time);
+	accu = min_t(unsigned long long, div_u64(accu, 100),
+					DEFAULT_ACCURACY_CLASS);
+
+	node = rb_first_cached(root);
+next:
+	re = rb_entry_safe(node, struct rb_entry, rb_node);
+	if (!re)
+		return;
+
+	ve = (struct victim_entry *)re;
+
+	if (ve->mtime >= max_mtime || ve->mtime < min_mtime)
+		goto skip;
+
+	/* age = 10000 * x% * 60 */
+	age = div64_u64(accu * (max_mtime - ve->mtime), total_time) *
+								age_weight;
+
+	vblocks = get_valid_blocks(sbi, ve->segno, true);
+	f2fs_bug_on(sbi, !vblocks || vblocks == sec_blocks);
+
+	/* u = 10000 * x% * 40 */
+	u = div64_u64(accu * (sec_blocks - vblocks), sec_blocks) *
+							(100 - age_weight);
+
+	f2fs_bug_on(sbi, age + u >= UINT_MAX);
+
+	cost = UINT_MAX - (age + u);
+	iter++;
+
+	if (cost < p->min_cost ||
+			(cost == p->min_cost && age > p->oldest_age)) {
+		p->min_cost = cost;
+		p->oldest_age = age;
+		p->min_segno = ve->segno;
+	}
+skip:
+	if (iter < dirty_threshold) {
+		node = rb_next(node);
+		goto next;
+	}
+}
+
+/*
+ * select candidates around source section in range of
+ * [target - dirty_threshold, target + dirty_threshold]
+ */
+static void atssr_lookup_victim(struct f2fs_sb_info *sbi,
+						struct victim_sel_policy *p)
+{
+	struct sit_info *sit_i = SIT_I(sbi);
+	struct atgc_management *am = &sbi->am;
+	struct rb_node *node;
+	struct rb_entry *re;
+	struct victim_entry *ve;
+	unsigned long long age;
+	unsigned long long max_mtime = sit_i->dirty_max_mtime;
+	unsigned long long min_mtime = sit_i->dirty_min_mtime;
+	unsigned int seg_blocks = sbi->blocks_per_seg;
+	unsigned int vblocks;
+	unsigned int dirty_threshold = max(am->max_candidate_count,
+					am->candidate_ratio *
+					am->victim_count / 100);
+	unsigned int cost;
+	unsigned int iter = 0;
+	int stage = 0;
+
+	if (max_mtime < min_mtime)
+		return;
+	max_mtime += 1;
+next_stage:
+	node = lookup_central_victim(sbi, p);
+next_node:
+	re = rb_entry_safe(node, struct rb_entry, rb_node);
+	if (!re) {
+		if (stage == 0)
+			goto skip_stage;
+		return;
+	}
+
+	ve = (struct victim_entry *)re;
+
+	if (ve->mtime >= max_mtime || ve->mtime < min_mtime)
+		goto skip_node;
+
+	age = max_mtime - ve->mtime;
+
+	vblocks = get_seg_entry(sbi, ve->segno)->ckpt_valid_blocks;
+	f2fs_bug_on(sbi, !vblocks);
+
+	/* rare case */
+	if (vblocks == seg_blocks)
+		goto skip_node;
+
+	iter++;
+
+	age = max_mtime - abs(p->age - age);
+	cost = UINT_MAX - vblocks;
+
+	if (cost < p->min_cost ||
+			(cost == p->min_cost && age > p->oldest_age)) {
+		p->min_cost = cost;
+		p->oldest_age = age;
+		p->min_segno = ve->segno;
+	}
+skip_node:
+	if (iter < dirty_threshold) {
+		if (stage == 0)
+			node = rb_prev(node);
+		else if (stage == 1)
+			node = rb_next(node);
+		goto next_node;
+	}
+skip_stage:
+	if (stage < 1) {
+		stage++;
+		iter = 0;
+		goto next_stage;
+	}
+}
+static void lookup_victim_by_age(struct f2fs_sb_info *sbi,
+						struct victim_sel_policy *p)
+{
+	f2fs_bug_on(sbi, !f2fs_check_rb_tree_consistence(sbi,
+						&sbi->am.root, true));
+
+	if (p->gc_mode == GC_AT)
+		atgc_lookup_victim(sbi, p);
+	else if (p->alloc_mode == AT_SSR)
+		atssr_lookup_victim(sbi, p);
+	else
+		f2fs_bug_on(sbi, 1);
+}
+
+static void release_victim_entry(struct f2fs_sb_info *sbi)
+{
+	struct atgc_management *am = &sbi->am;
+	struct victim_entry *ve, *tmp;
+
+	list_for_each_entry_safe(ve, tmp, &am->victim_list, list) {
+		list_del(&ve->list);
+		kmem_cache_free(victim_entry_slab, ve);
+		am->victim_count--;
+	}
+
+	am->root = RB_ROOT_CACHED;
+
+	f2fs_bug_on(sbi, am->victim_count);
+	f2fs_bug_on(sbi, !list_empty(&am->victim_list));
+}
+
 /*
  * This function is called from two paths.
  * One is garbage collection and the other is SSR segment selection.
@@ -322,25 +609,37 @@ static unsigned int count_bits(const unsigned long *addr,
  * 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)
+			unsigned int *result, int gc_type, int type,
+			char alloc_mode, unsigned long long age)
 {
 	struct dirty_seglist_info *dirty_i = DIRTY_I(sbi);
 	struct sit_info *sm = SIT_I(sbi);
 	struct victim_sel_policy p;
 	unsigned int secno, last_victim;
 	unsigned int last_segment;
-	unsigned int nsearched = 0;
+	unsigned int nsearched;
+	bool is_atgc;
 	int ret = 0;
 
 	mutex_lock(&dirty_i->seglist_lock);
 	last_segment = MAIN_SECS(sbi) * sbi->segs_per_sec;
 
 	p.alloc_mode = alloc_mode;
-	select_policy(sbi, gc_type, type, &p);
+	p.age = age;
+	p.age_threshold = sbi->am.age_threshold;
 
+retry:
+	select_policy(sbi, gc_type, type, &p);
 	p.min_segno = NULL_SEGNO;
+	p.oldest_age = 0;
 	p.min_cost = get_max_cost(sbi, &p);
 
+	is_atgc = (p.gc_mode == GC_AT || p.alloc_mode == AT_SSR);
+	nsearched = 0;
+
+	if (is_atgc)
+		SIT_I(sbi)->dirty_min_mtime = ULLONG_MAX;
+
 	if (*result != NULL_SEGNO) {
 		if (!get_valid_blocks(sbi, *result, false)) {
 			ret = -ENODATA;
@@ -426,6 +725,11 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
 		if (gc_type == BG_GC && test_bit(secno, dirty_i->victim_secmap))
 			goto next;
 
+		if (is_atgc) {
+			add_victim_entry(sbi, &p, segno);
+			goto next;
+		}
+
 		cost = get_gc_cost(sbi, segno, &p);
 
 		if (p.min_cost > cost) {
@@ -444,6 +748,19 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
 			break;
 		}
 	}
+
+	/* get victim for GC_AT/AT_SSR */
+	if (is_atgc) {
+		lookup_victim_by_age(sbi, &p);
+		release_victim_entry(sbi);
+	}
+
+	if (is_atgc && p.min_segno == NULL_SEGNO &&
+			sm->elapsed_time < p.age_threshold) {
+		p.age_threshold = 0;
+		goto retry;
+	}
+
 	if (p.min_segno != NULL_SEGNO) {
 got_it:
 		*result = (p.min_segno / p.ofs_unit) * p.ofs_unit;
@@ -791,6 +1108,8 @@ static int move_data_block(struct inode *inode, block_t bidx,
 	block_t newaddr;
 	int err = 0;
 	bool lfs_mode = f2fs_lfs_mode(fio.sbi);
+	int type = fio.sbi->am.atgc_enabled ?
+				CURSEG_ALL_DATA_ATGC : CURSEG_COLD_DATA;
 
 	/* do not read out */
 	page = f2fs_grab_cache_page(inode->i_mapping, bidx, false);
@@ -877,7 +1196,7 @@ static int move_data_block(struct inode *inode, block_t bidx,
 	}
 
 	f2fs_allocate_data_block(fio.sbi, NULL, fio.old_blkaddr, &newaddr,
-				&sum, CURSEG_COLD_DATA, NULL, true);
+				&sum, type, NULL);
 
 	fio.encrypted_page = f2fs_pagecache_get_page(META_MAPPING(fio.sbi),
 				newaddr, FGP_LOCK | FGP_CREAT, GFP_NOFS);
@@ -1182,7 +1501,7 @@ static int __get_victim(struct f2fs_sb_info *sbi, unsigned int *victim,
 
 	down_write(&sit_i->sentry_lock);
 	ret = DIRTY_I(sbi)->v_ops->get_victim(sbi, victim, gc_type,
-					      NO_CHECK_TYPE, LFS);
+					      NO_CHECK_TYPE, LFS, 0);
 	up_write(&sit_i->sentry_lock);
 	return ret;
 }
@@ -1204,6 +1523,8 @@ static int do_garbage_collect(struct f2fs_sb_info *sbi,
 	if (__is_large_section(sbi))
 		end_segno = rounddown(end_segno, sbi->segs_per_sec);
 
+	sanity_check_seg_type(sbi, get_seg_entry(sbi, segno)->type);
+
 	/* readahead multi ssa blocks those have contiguous address */
 	if (__is_large_section(sbi))
 		f2fs_ra_meta_pages(sbi, GET_SUM_BLOCK(sbi, segno),
@@ -1413,6 +1734,37 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
 	return ret;
 }
 
+int __init f2fs_create_garbage_collection_cache(void)
+{
+	victim_entry_slab = f2fs_kmem_cache_create("f2fs_victim_entry",
+					sizeof(struct victim_entry));
+	if (!victim_entry_slab)
+		return -ENOMEM;
+	return 0;
+}
+
+void f2fs_destroy_garbage_collection_cache(void)
+{
+	kmem_cache_destroy(victim_entry_slab);
+}
+
+static void init_atgc_management(struct f2fs_sb_info *sbi)
+{
+	struct atgc_management *am = &sbi->am;
+
+	if (test_opt(sbi, ATGC) &&
+		SIT_I(sbi)->elapsed_time >= DEF_GC_THREAD_AGE_THRESHOLD)
+		am->atgc_enabled = true;
+
+	am->root = RB_ROOT_CACHED;
+	INIT_LIST_HEAD(&am->victim_list);
+	am->victim_count = 0;
+
+	am->candidate_ratio = DEF_GC_THREAD_CANDIDATE_RATIO;
+	am->max_candidate_count = DEF_GC_THREAD_MAX_CANDIDATE_COUNT;
+	am->age_weight = DEF_GC_THREAD_AGE_WEIGHT;
+}
+
 void f2fs_build_gc_manager(struct f2fs_sb_info *sbi)
 {
 	DIRTY_I(sbi)->v_ops = &default_v_ops;
@@ -1423,6 +1775,8 @@ void f2fs_build_gc_manager(struct f2fs_sb_info *sbi)
 	if (f2fs_is_multi_device(sbi) && !__is_large_section(sbi))
 		SIT_I(sbi)->last_victim[ALLOC_NEXT] =
 				GET_SEGNO(sbi, FDEV(0).end_blk) + 1;
+
+	init_atgc_management(sbi);
 }
 
 static int free_segment_range(struct f2fs_sb_info *sbi,
diff --git a/fs/f2fs/gc.h b/fs/f2fs/gc.h
index db3c61046aa4..853287b2b45c 100644
--- a/fs/f2fs/gc.h
+++ b/fs/f2fs/gc.h
@@ -14,6 +14,14 @@
 #define DEF_GC_THREAD_MIN_SLEEP_TIME	30000	/* milliseconds */
 #define DEF_GC_THREAD_MAX_SLEEP_TIME	60000
 #define DEF_GC_THREAD_NOGC_SLEEP_TIME	300000	/* wait 5 min */
+
+/* choose candidates from sections which has age of more than 7 days */
+#define DEF_GC_THREAD_AGE_THRESHOLD		(60 * 60 * 24 * 7)
+#define DEF_GC_THREAD_CANDIDATE_RATIO		20	/* select 20% oldest sections as candidates */
+#define DEF_GC_THREAD_MAX_CANDIDATE_COUNT	10	/* select at most 10 sections as candidates */
+#define DEF_GC_THREAD_AGE_WEIGHT		60	/* age weight */
+#define DEFAULT_ACCURACY_CLASS			10000	/* accuracy class */
+
 #define LIMIT_INVALID_BLOCK	40 /* percentage over total user space */
 #define LIMIT_FREE_BLOCK	40 /* percentage over invalid + free space */
 
@@ -41,6 +49,23 @@ struct gc_inode_list {
 	struct radix_tree_root iroot;
 };
 
+struct victim_info {
+	unsigned long long mtime;	/* mtime of section */
+	unsigned int segno;		/* section No. */
+};
+
+struct victim_entry {
+	struct rb_node rb_node;		/* rb node located in rb-tree */
+	union {
+		struct {
+			unsigned long long mtime;	/* mtime of section */
+			unsigned int segno;		/* segment No. */
+		};
+		struct victim_info vi;	/* victim info */
+	};
+	struct list_head list;
+};
+
 /*
  * inline functions
  */
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index f89219db72a2..5a5f5ad2e865 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -2420,9 +2420,9 @@ static void write_current_sum_page(struct f2fs_sb_info *sbi,
 	f2fs_put_page(page, 1);
 }
 
-static int is_next_segment_free(struct f2fs_sb_info *sbi, int type)
+static int is_next_segment_free(struct f2fs_sb_info *sbi,
+				struct curseg_info *curseg, int type)
 {
-	struct curseg_info *curseg = CURSEG_I(sbi, type);
 	unsigned int segno = curseg->segno + 1;
 	struct free_segmap_info *free_i = FREE_I(sbi);
 
@@ -2526,6 +2526,7 @@ static void reset_curseg(struct f2fs_sb_info *sbi, int type, int modified)
 {
 	struct curseg_info *curseg = CURSEG_I(sbi, type);
 	struct summary_footer *sum_footer;
+	unsigned short seg_type = curseg->seg_type;
 
 	curseg->inited = true;
 	curseg->segno = curseg->next_segno;
@@ -2535,16 +2536,22 @@ static void reset_curseg(struct f2fs_sb_info *sbi, int type, int modified)
 
 	sum_footer = &(curseg->sum_blk->footer);
 	memset(sum_footer, 0, sizeof(struct summary_footer));
-	if (IS_DATASEG(curseg->seg_type))
+
+	sanity_check_seg_type(sbi, seg_type);
+
+	if (IS_DATASEG(seg_type))
 		SET_SUM_TYPE(sum_footer, SUM_TYPE_DATA);
-	if (IS_NODESEG(curseg->seg_type))
+	if (IS_NODESEG(seg_type))
 		SET_SUM_TYPE(sum_footer, SUM_TYPE_NODE);
-	__set_sit_entry_type(sbi, curseg->seg_type, curseg->segno, modified);
+	__set_sit_entry_type(sbi, seg_type, curseg->segno, modified);
 }
 
 static unsigned int __get_next_segno(struct f2fs_sb_info *sbi, int type)
 {
 	struct curseg_info *curseg = CURSEG_I(sbi, type);
+	unsigned short seg_type = curseg->seg_type;
+
+	sanity_check_seg_type(sbi, seg_type);
 
 	/* if segs_per_sec is large than 1, we need to keep original policy. */
 	if (__is_large_section(sbi))
@@ -2558,8 +2565,7 @@ static unsigned int __get_next_segno(struct f2fs_sb_info *sbi, int type)
 		return 0;
 
 	if (test_opt(sbi, NOHEAP) &&
-		(curseg->seg_type == CURSEG_HOT_DATA ||
-		IS_NODESEG(curseg->seg_type)))
+		(seg_type == CURSEG_HOT_DATA || IS_NODESEG(seg_type)))
 		return 0;
 
 	if (SIT_I(sbi)->last_victim[ALLOC_NEXT])
@@ -2635,7 +2641,7 @@ static void __refresh_next_blkoff(struct f2fs_sb_info *sbi,
  * This function always allocates a used segment(from dirty seglist) by SSR
  * manner, so it should recover the existing segment information of valid blocks
  */
-static void change_curseg(struct f2fs_sb_info *sbi, int type)
+static void change_curseg(struct f2fs_sb_info *sbi, int type, bool flush)
 {
 	struct dirty_seglist_info *dirty_i = DIRTY_I(sbi);
 	struct curseg_info *curseg = CURSEG_I(sbi, type);
@@ -2643,8 +2649,10 @@ static void change_curseg(struct f2fs_sb_info *sbi, int type)
 	struct f2fs_summary_block *sum_node;
 	struct page *sum_page;
 
-	write_sum_page(sbi, curseg->sum_blk,
-				GET_SUM_BLOCK(sbi, curseg->segno));
+	if (flush)
+		write_sum_page(sbi, curseg->sum_blk,
+					GET_SUM_BLOCK(sbi, curseg->segno));
+
 	__set_test_and_inuse(sbi, new_segno);
 
 	mutex_lock(&dirty_i->seglist_lock);
@@ -2663,10 +2671,62 @@ static void change_curseg(struct f2fs_sb_info *sbi, int type)
 	f2fs_put_page(sum_page, 1);
 }
 
-void f2fs_save_inmem_curseg(struct f2fs_sb_info *sbi, int type)
+static int get_ssr_segment(struct f2fs_sb_info *sbi, int type,
+				int alloc_mode, unsigned long long age);
+
+static void get_atssr_segment(struct f2fs_sb_info *sbi, int type,
+					int target_type, int alloc_mode,
+					unsigned long long age)
 {
 	struct curseg_info *curseg = CURSEG_I(sbi, type);
 
+	curseg->seg_type = target_type;
+
+	if (get_ssr_segment(sbi, type, alloc_mode, age)) {
+		struct seg_entry *se = get_seg_entry(sbi, curseg->next_segno);
+
+		curseg->seg_type = se->type;
+		change_curseg(sbi, type, true);
+	} else {
+		/* allocate cold segment by default */
+		curseg->seg_type = CURSEG_COLD_DATA;
+		new_curseg(sbi, type, true);
+	}
+	stat_inc_seg_type(sbi, curseg);
+}
+
+static void __f2fs_init_atgc_curseg(struct f2fs_sb_info *sbi)
+{
+	struct curseg_info *curseg = CURSEG_I(sbi, CURSEG_ALL_DATA_ATGC);
+
+	if (!sbi->am.atgc_enabled)
+		return;
+
+	down_read(&SM_I(sbi)->curseg_lock);
+
+	mutex_lock(&curseg->curseg_mutex);
+	down_write(&SIT_I(sbi)->sentry_lock);
+
+	get_atssr_segment(sbi, CURSEG_ALL_DATA_ATGC, CURSEG_COLD_DATA, SSR, 0);
+
+	up_write(&SIT_I(sbi)->sentry_lock);
+	mutex_unlock(&curseg->curseg_mutex);
+
+	up_read(&SM_I(sbi)->curseg_lock);
+
+}
+void f2fs_init_inmem_curseg(struct f2fs_sb_info *sbi)
+{
+	__f2fs_init_atgc_curseg(sbi);
+}
+
+static void __f2fs_save_inmem_curseg(struct f2fs_sb_info *sbi, int type)
+{
+	struct curseg_info *curseg = CURSEG_I(sbi, type);
+
+	if (!sbi->am.atgc_enabled)
+		return;
+
 	mutex_lock(&curseg->curseg_mutex);
 	if (!curseg->inited)
 		goto out;
@@ -2683,10 +2743,21 @@ void f2fs_save_inmem_curseg(struct f2fs_sb_info *sbi, int type)
 	mutex_unlock(&curseg->curseg_mutex);
 }
 
-void f2fs_restore_inmem_curseg(struct f2fs_sb_info *sbi, int type)
+void f2fs_save_inmem_curseg(struct f2fs_sb_info *sbi)
+{
+	__f2fs_save_inmem_curseg(sbi, CURSEG_COLD_DATA_PINNED);
+
+	if (sbi->am.atgc_enabled)
+		__f2fs_save_inmem_curseg(sbi, CURSEG_ALL_DATA_ATGC);
+}
+
+static void __f2fs_restore_inmem_curseg(struct f2fs_sb_info *sbi, int type)
 {
 	struct curseg_info *curseg = CURSEG_I(sbi, type);
 
+	if (!sbi->am.atgc_enabled)
+		return;
+
 	mutex_lock(&curseg->curseg_mutex);
 	if (!curseg->inited)
 		goto out;
@@ -2700,23 +2771,35 @@ void f2fs_restore_inmem_curseg(struct f2fs_sb_info *sbi, int type)
 	mutex_unlock(&curseg->curseg_mutex);
 }
 
-static int get_ssr_segment(struct f2fs_sb_info *sbi, int type)
+void f2fs_restore_inmem_curseg(struct f2fs_sb_info *sbi)
+{
+	__f2fs_restore_inmem_curseg(sbi, CURSEG_COLD_DATA_PINNED);
+
+	if (sbi->am.atgc_enabled)
+		__f2fs_restore_inmem_curseg(sbi, CURSEG_ALL_DATA_ATGC);
+}
+
+static int get_ssr_segment(struct f2fs_sb_info *sbi, int type,
+				int alloc_mode, unsigned long long age)
 {
 	struct curseg_info *curseg = CURSEG_I(sbi, type);
 	const struct victim_selection *v_ops = DIRTY_I(sbi)->v_ops;
 	unsigned segno = NULL_SEGNO;
+	unsigned short seg_type = curseg->seg_type;
 	int i, cnt;
 	bool reversed = false;
 
+	sanity_check_seg_type(sbi, seg_type);
+
 	/* f2fs_need_SSR() already forces to do this */
-	if (!v_ops->get_victim(sbi, &segno, BG_GC, type, SSR)) {
+	if (!v_ops->get_victim(sbi, &segno, BG_GC, seg_type, alloc_mode, age)) {
 		curseg->next_segno = segno;
 		return 1;
 	}
 
 	/* For node segments, let's do SSR more intensively */
-	if (IS_NODESEG(type)) {
-		if (type >= CURSEG_WARM_NODE) {
+	if (IS_NODESEG(seg_type)) {
+		if (seg_type >= CURSEG_WARM_NODE) {
 			reversed = true;
 			i = CURSEG_COLD_NODE;
 		} else {
@@ -2724,7 +2807,7 @@ static int get_ssr_segment(struct f2fs_sb_info *sbi, int type)
 		}
 		cnt = NR_CURSEG_NODE_TYPE;
 	} else {
-		if (type >= CURSEG_WARM_DATA) {
+		if (seg_type >= CURSEG_WARM_DATA) {
 			reversed = true;
 			i = CURSEG_COLD_DATA;
 		} else {
@@ -2734,9 +2817,9 @@ static int get_ssr_segment(struct f2fs_sb_info *sbi, int type)
 	}
 
 	for (; cnt-- > 0; reversed ? i-- : i++) {
-		if (i == type)
+		if (i == seg_type)
 			continue;
-		if (!v_ops->get_victim(sbi, &segno, BG_GC, i, SSR)) {
+		if (!v_ops->get_victim(sbi, &segno, BG_GC, i, alloc_mode, age)) {
 			curseg->next_segno = segno;
 			return 1;
 		}
@@ -2765,13 +2848,15 @@ static void allocate_segment_by_default(struct f2fs_sb_info *sbi,
 	if (force)
 		new_curseg(sbi, type, true);
 	else if (!is_set_ckpt_flags(sbi, CP_CRC_RECOVERY_FLAG) &&
-					type == CURSEG_WARM_NODE)
+					curseg->seg_type == CURSEG_WARM_NODE)
 		new_curseg(sbi, type, false);
-	else if (curseg->alloc_type == LFS && is_next_segment_free(sbi, type) &&
+	else if (curseg->alloc_type == LFS &&
+			is_next_segment_free(sbi, curseg, type) &&
 			likely(!is_sbi_flag_set(sbi, SBI_CP_DISABLED)))
 		new_curseg(sbi, type, false);
-	else if (f2fs_need_SSR(sbi) && get_ssr_segment(sbi, type))
-		change_curseg(sbi, type);
+	else if (f2fs_need_SSR(sbi) &&
+			get_ssr_segment(sbi, type, SSR, 0))
+		change_curseg(sbi, type, true);
 	else
 		new_curseg(sbi, type, false);
 
@@ -2792,8 +2877,8 @@ void f2fs_allocate_segment_for_resize(struct f2fs_sb_info *sbi, int type,
 	if (segno < start || segno > end)
 		goto unlock;
 
-	if (f2fs_need_SSR(sbi) && get_ssr_segment(sbi, type))
-		change_curseg(sbi, type);
+	if (f2fs_need_SSR(sbi) && get_ssr_segment(sbi, type, SSR, 0))
+		change_curseg(sbi, type, true);
 	else
 		new_curseg(sbi, type, true);
 
@@ -3012,9 +3097,9 @@ int f2fs_trim_fs(struct f2fs_sb_info *sbi, struct fstrim_range *range)
 	return err;
 }
 
-static bool __has_curseg_space(struct f2fs_sb_info *sbi, int type)
+static bool __has_curseg_space(struct f2fs_sb_info *sbi,
+					struct curseg_info *curseg)
 {
-	struct curseg_info *curseg = CURSEG_I(sbi, type);
 	if (curseg->next_blkoff < sbi->blocks_per_seg)
 		return true;
 	return false;
@@ -3157,8 +3242,13 @@ static int __get_segment_type_6(struct f2fs_io_info *fio)
 	if (fio->type == DATA) {
 		struct inode *inode = fio->page->mapping->host;
 
-		if (is_cold_data(fio->page) || file_is_cold(inode) ||
-				f2fs_compressed_file(inode))
+		if (is_cold_data(fio->page)) {
+			if (fio->sbi->am.atgc_enabled)
+				return CURSEG_ALL_DATA_ATGC;
+			else
+				return CURSEG_COLD_DATA;
+		}
+		if (file_is_cold(inode) || f2fs_compressed_file(inode))
 			return CURSEG_COLD_DATA;
 		if (file_is_hot(inode) ||
 				is_inode_flag_set(inode, FI_HOT_DATA) ||
@@ -3204,19 +3294,29 @@ static int __get_segment_type(struct f2fs_io_info *fio)
 void f2fs_allocate_data_block(struct f2fs_sb_info *sbi, struct page *page,
 		block_t old_blkaddr, block_t *new_blkaddr,
 		struct f2fs_summary *sum, int type,
-		struct f2fs_io_info *fio, bool from_gc)
+		struct f2fs_io_info *fio)
 {
 	struct sit_info *sit_i = SIT_I(sbi);
 	struct curseg_info *curseg = CURSEG_I(sbi, type);
 	unsigned long long old_mtime;
+	bool from_gc = (type == CURSEG_ALL_DATA_ATGC);
+	struct seg_entry *se;
 
 	down_read(&SM_I(sbi)->curseg_lock);
 
 	mutex_lock(&curseg->curseg_mutex);
 	down_write(&sit_i->sentry_lock);
 
+	if (from_gc) {
+		f2fs_bug_on(sbi, GET_SEGNO(sbi, old_blkaddr) == NULL_SEGNO);
+		se = get_seg_entry(sbi, GET_SEGNO(sbi, old_blkaddr));
+		sanity_check_seg_type(sbi, se->type);
+		f2fs_bug_on(sbi, IS_NODESEG(se->type));
+	}
 	*new_blkaddr = NEXT_FREE_BLKADDR(sbi, curseg);
 
+	f2fs_bug_on(sbi, curseg->next_blkoff >= sbi->blocks_per_seg);
+
 	f2fs_wait_discard_bio(sbi, *new_blkaddr);
 
 	/*
@@ -3246,9 +3346,13 @@ void f2fs_allocate_data_block(struct f2fs_sb_info *sbi, struct page *page,
 	if (GET_SEGNO(sbi, old_blkaddr) != NULL_SEGNO)
 		update_sit_entry(sbi, old_blkaddr, -1);
 
-	if (!__has_curseg_space(sbi, type))
-		sit_i->s_ops->allocate_segment(sbi, type, false);
-
+	if (!__has_curseg_space(sbi, curseg)) {
+		if (from_gc)
+			get_atssr_segment(sbi, type, se->type,
+						AT_SSR, se->mtime);
+		else
+			sit_i->s_ops->allocate_segment(sbi, type, false);
+	}
 	/*
 	 * segment dirty status should be updated after segment allocation,
 	 * so we just need to update status only one time after previous
@@ -3314,8 +3418,7 @@ static void do_write_page(struct f2fs_summary *sum, struct f2fs_io_info *fio)
 		down_read(&fio->sbi->io_order_lock);
 reallocate:
 	f2fs_allocate_data_block(fio->sbi, fio->page, fio->old_blkaddr,
-			&fio->new_blkaddr, sum, type, fio,
-			is_cold_data(fio->page));
+			&fio->new_blkaddr, sum, type, fio);
 	if (GET_SEGNO(fio->sbi, fio->old_blkaddr) != NULL_SEGNO)
 		invalidate_mapping_pages(META_MAPPING(fio->sbi),
 					fio->old_blkaddr, fio->old_blkaddr);
@@ -3477,7 +3580,7 @@ void f2fs_do_replace_block(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
 	/* change the current segment */
 	if (segno != curseg->segno) {
 		curseg->next_segno = segno;
-		change_curseg(sbi, type);
+		change_curseg(sbi, type, true);
 	}
 
 	curseg->next_blkoff = GET_BLKOFF_FROM_SEG0(sbi, new_blkaddr);
@@ -3504,7 +3607,7 @@ void f2fs_do_replace_block(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
 	if (recover_curseg) {
 		if (old_cursegno != curseg->segno) {
 			curseg->next_segno = old_cursegno;
-			change_curseg(sbi, type);
+			change_curseg(sbi, type, true);
 		}
 		curseg->next_blkoff = old_blkoff;
 	}
@@ -4259,6 +4362,8 @@ static int build_curseg(struct f2fs_sb_info *sbi)
 			array[i].seg_type = CURSEG_HOT_DATA + i;
 		else if (i == CURSEG_COLD_DATA_PINNED)
 			array[i].seg_type = CURSEG_COLD_DATA;
+		else if (i == CURSEG_ALL_DATA_ATGC)
+			array[i].seg_type = CURSEG_COLD_DATA;
 		array[i].segno = NULL_SEGNO;
 		array[i].next_blkoff = 0;
 		array[i].inited = false;
@@ -4501,6 +4606,8 @@ static int sanity_check_curseg(struct f2fs_sb_info *sbi)
 		struct seg_entry *se = get_seg_entry(sbi, curseg->segno);
 		unsigned int blkofs = curseg->next_blkoff;
 
+		sanity_check_seg_type(sbi, curseg->seg_type);
+
 		if (f2fs_test_bit(blkofs, se->cur_valid_map))
 			goto out;
 
@@ -4803,6 +4910,7 @@ static void init_min_max_mtime(struct f2fs_sb_info *sbi)
 			sit_i->min_mtime = mtime;
 	}
 	sit_i->max_mtime = get_mtime(sbi, false);
+	sit_i->dirty_max_mtime = 0;
 	up_write(&sit_i->sentry_lock);
 }
 
diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
index 515d9ed2cd95..47a5c464603f 100644
--- a/fs/f2fs/segment.h
+++ b/fs/f2fs/segment.h
@@ -24,6 +24,12 @@
 #define IS_DATASEG(t)	((t) <= CURSEG_COLD_DATA)
 #define IS_NODESEG(t)	((t) >= CURSEG_HOT_NODE && (t) <= CURSEG_COLD_NODE)
 
+static inline void sanity_check_seg_type(struct f2fs_sb_info *sbi,
+						unsigned short seg_type)
+{
+	f2fs_bug_on(sbi, seg_type >= NR_PERSISTENT_LOG);
+}
+
 #define IS_HOT(t)	((t) == CURSEG_HOT_NODE || (t) == CURSEG_HOT_DATA)
 #define IS_WARM(t)	((t) == CURSEG_WARM_NODE || (t) == CURSEG_WARM_DATA)
 #define IS_COLD(t)	((t) == CURSEG_COLD_NODE || (t) == CURSEG_COLD_DATA)
@@ -35,7 +41,8 @@
 	 ((seg) == CURSEG_I(sbi, CURSEG_HOT_NODE)->segno) ||	\
 	 ((seg) == CURSEG_I(sbi, CURSEG_WARM_NODE)->segno) ||	\
 	 ((seg) == CURSEG_I(sbi, CURSEG_COLD_NODE)->segno) ||	\
-	 ((seg) == CURSEG_I(sbi, CURSEG_COLD_DATA_PINNED)->segno))
+	 ((seg) == CURSEG_I(sbi, CURSEG_COLD_DATA_PINNED)->segno) ||	\
+	 ((seg) == CURSEG_I(sbi, CURSEG_ALL_DATA_ATGC)->segno))
 
 #define IS_CURSEC(sbi, secno)						\
 	(((secno) == CURSEG_I(sbi, CURSEG_HOT_DATA)->segno /		\
@@ -51,6 +58,8 @@
 	 ((secno) == CURSEG_I(sbi, CURSEG_COLD_NODE)->segno /		\
 	  (sbi)->segs_per_sec) ||	\
 	 ((secno) == CURSEG_I(sbi, CURSEG_COLD_DATA_PINNED)->segno /	\
+	  (sbi)->segs_per_sec) ||	\
+	 ((secno) == CURSEG_I(sbi, CURSEG_ALL_DATA_ATGC)->segno /	\
 	  (sbi)->segs_per_sec))
 
 #define MAIN_BLKADDR(sbi)						\
@@ -135,20 +144,25 @@ enum {
  * In the victim_sel_policy->alloc_mode, there are two block allocation modes.
  * LFS writes data sequentially with cleaning operations.
  * SSR (Slack Space Recycle) reuses obsolete space without cleaning operations.
+ * AT_SSR (Age Threshold based Slack Space Recycle) merges fragments into
+ * fragmented segment which has similar aging degree.
  */
 enum {
 	LFS = 0,
-	SSR
+	SSR,
+	AT_SSR,
 };
 
 /*
  * In the victim_sel_policy->gc_mode, there are two gc, aka cleaning, modes.
  * GC_CB is based on cost-benefit algorithm.
  * GC_GREEDY is based on greedy algorithm.
+ * GC_AT is based on age-threshold algorithm.
  */
 enum {
 	GC_CB = 0,
 	GC_GREEDY,
+	GC_AT,
 	ALLOC_NEXT,
 	FLUSH_DEVICE,
 	MAX_GC_POLICY,
@@ -177,7 +191,10 @@ struct victim_sel_policy {
 	unsigned int offset;		/* last scanned bitmap offset */
 	unsigned int ofs_unit;		/* bitmap search unit */
 	unsigned int min_cost;		/* minimum cost */
+	unsigned long long oldest_age;	/* oldest age of segments having the same min cost */
 	unsigned int min_segno;		/* segment # having min. cost */
+	unsigned long long age;		/* mtime of GCed section*/
+	unsigned long long age_threshold;/* age threshold */
 };
 
 struct seg_entry {
@@ -243,6 +260,8 @@ struct sit_info {
 	unsigned long long mounted_time;	/* mount time */
 	unsigned long long min_mtime;		/* min. modification time */
 	unsigned long long max_mtime;		/* max. modification time */
+	unsigned long long dirty_min_mtime;	/* rerange candidates in GC_AT */
+	unsigned long long dirty_max_mtime;	/* rerange candidates in GC_AT */
 
 	unsigned int last_victim[MAX_GC_POLICY]; /* last victim segment # */
 };
@@ -281,7 +300,7 @@ struct dirty_seglist_info {
 /* victim selection function for cleaning and SSR */
 struct victim_selection {
 	int (*get_victim)(struct f2fs_sb_info *, unsigned int *,
-							int, int, char);
+					int, int, char, unsigned long long);
 };
 
 /* for active log information */
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index bf90c8caeb1e..e391079587ac 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -145,6 +145,7 @@ enum {
 	Opt_compress_algorithm,
 	Opt_compress_log_size,
 	Opt_compress_extension,
+	Opt_atgc,
 	Opt_err,
 };
 
@@ -211,6 +212,7 @@ static match_table_t f2fs_tokens = {
 	{Opt_compress_algorithm, "compress_algorithm=%s"},
 	{Opt_compress_log_size, "compress_log_size=%u"},
 	{Opt_compress_extension, "compress_extension=%s"},
+	{Opt_atgc, "atgc"},
 	{Opt_err, NULL},
 };
 
@@ -930,6 +932,9 @@ static int parse_options(struct super_block *sb, char *options, bool is_remount)
 			f2fs_info(sbi, "compression options not supported");
 			break;
 #endif
+		case Opt_atgc:
+			set_opt(sbi, ATGC);
+			break;
 		default:
 			f2fs_err(sbi, "Unrecognized mount option \"%s\" or missing value",
 				 p);
@@ -1623,6 +1628,9 @@ static int f2fs_show_options(struct seq_file *seq, struct dentry *root)
 #ifdef CONFIG_F2FS_FS_COMPRESSION
 	f2fs_show_compress_options(seq, sbi->sb);
 #endif
+
+	if (test_opt(sbi, ATGC))
+		seq_puts(seq, ",atgc");
 	return 0;
 }
 
@@ -1750,6 +1758,7 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
 	bool no_extent_cache = !test_opt(sbi, EXTENT_CACHE);
 	bool disable_checkpoint = test_opt(sbi, DISABLE_CHECKPOINT);
 	bool no_io_align = !F2FS_IO_ALIGNED(sbi);
+	bool no_atgc = !test_opt(sbi, ATGC);
 	bool checkpoint_changed;
 #ifdef CONFIG_QUOTA
 	int i, j;
@@ -1822,6 +1831,13 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
 		}
 	}
 #endif
+	/* disallow enable atgc dynamically */
+	if (no_atgc == !!test_opt(sbi, ATGC)) {
+		err = -EINVAL;
+		f2fs_warn(sbi, "switch atgc option is not allowed");
+		goto restore_opts;
+	}
+
 	/* disallow enable/disable extent_cache dynamically */
 	if (no_extent_cache == !!test_opt(sbi, EXTENT_CACHE)) {
 		err = -EINVAL;
@@ -3728,6 +3744,8 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
 	}
 
 reset_checkpoint:
+	f2fs_init_inmem_curseg(sbi);
+
 	/* f2fs_recover_fsync_data() cleared this already */
 	clear_sbi_flag(sbi, SBI_POR_DOING);
 
@@ -3933,9 +3951,12 @@ static int __init init_f2fs_fs(void)
 	err = f2fs_create_extent_cache();
 	if (err)
 		goto free_checkpoint_caches;
-	err = f2fs_init_sysfs();
+	err = f2fs_create_garbage_collection_cache();
 	if (err)
 		goto free_extent_cache;
+	err = f2fs_init_sysfs();
+	if (err)
+		goto free_garbage_collection_cache;
 	err = register_shrinker(&f2fs_shrinker_info);
 	if (err)
 		goto free_sysfs;
@@ -3969,6 +3990,8 @@ static int __init init_f2fs_fs(void)
 	unregister_shrinker(&f2fs_shrinker_info);
 free_sysfs:
 	f2fs_exit_sysfs();
+free_garbage_collection_cache:
+	f2fs_destroy_garbage_collection_cache();
 free_extent_cache:
 	f2fs_destroy_extent_cache();
 free_checkpoint_caches:
@@ -3993,6 +4016,7 @@ static void __exit exit_f2fs_fs(void)
 	unregister_filesystem(&f2fs_fs_type);
 	unregister_shrinker(&f2fs_shrinker_info);
 	f2fs_exit_sysfs();
+	f2fs_destroy_garbage_collection_cache();
 	f2fs_destroy_extent_cache();
 	f2fs_destroy_checkpoint_caches();
 	f2fs_destroy_segment_manager_caches();
diff --git a/include/trace/events/f2fs.h b/include/trace/events/f2fs.h
index 8a1c1311acac..06c73f3f6dd2 100644
--- a/include/trace/events/f2fs.h
+++ b/include/trace/events/f2fs.h
@@ -111,13 +111,15 @@ TRACE_DEFINE_ENUM(CP_RESIZE);
 
 #define show_alloc_mode(type)						\
 	__print_symbolic(type,						\
-		{ LFS,	"LFS-mode" },					\
-		{ SSR,	"SSR-mode" })
+		{ LFS,		"LFS-mode" },				\
+		{ SSR,		"SSR-mode" },				\
+		{ AT_SSR,	"AT_SSR-mode" })
 
 #define show_victim_policy(type)					\
 	__print_symbolic(type,						\
 		{ GC_GREEDY,	"Greedy" },				\
-		{ GC_CB,	"Cost-Benefit" })
+		{ GC_CB,	"Cost-Benefit" },			\
+		{ GC_AT,	"Age-threshold" })
 
 #define show_cpreason(type)						\
 	__print_flags(type, "|",					\
-- 
2.26.2