5 files changed, 452 insertions, 15 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 67a675d222f2..42df628b35e5 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -162,7 +162,12 @@ enum SHIFT_DIRECTION {
 #define EXT4_MB_USE_RESERVED		0x2000
 /* Do strict check for free blocks while retrying block allocation */
 #define EXT4_MB_STRICT_CHECK		0x4000
-
+/* Large fragment size list lookup succeeded at least once for cr = 0 */
+#define EXT4_MB_CR0_OPTIMIZED		0x8000
+/* Avg fragment size rb tree lookup succeeded at least once for cr = 1 */
+#define EXT4_MB_CR1_OPTIMIZED		0x00010000
+/* Perform linear traversal for one group */
+#define EXT4_MB_SEARCH_NEXT_LINEAR	0x00020000
 struct ext4_allocation_request {
 	/* target inode for block we're allocating */
 	struct inode *inode;
@@ -1247,7 +1252,9 @@ struct ext4_inode_info {
 #define EXT4_MOUNT2_JOURNAL_FAST_COMMIT	0x00000010 /* Journal fast commit */
 #define EXT4_MOUNT2_DAX_NEVER		0x00000020 /* Do not allow Direct Access */
 #define EXT4_MOUNT2_DAX_INODE		0x00000040 /* For printing options only */
-
+#define EXT4_MOUNT2_MB_OPTIMIZE_SCAN	0x00000080 /* Optimize group
+						    * scanning in mballoc
+						    */
 
 #define clear_opt(sb, opt)		EXT4_SB(sb)->s_mount_opt &= \
 						~EXT4_MOUNT_##opt
@@ -1528,9 +1535,14 @@ struct ext4_sb_info {
 	unsigned int s_mb_free_pending;
 	struct list_head s_freed_data_list;	/* List of blocks to be freed
 						   after commit completed */
+	struct rb_root s_mb_avg_fragment_size_root;
+	rwlock_t s_mb_rb_lock;
+	struct list_head *s_mb_largest_free_orders;
+	rwlock_t *s_mb_largest_free_orders_locks;
 
 	/* tunables */
 	unsigned long s_stripe;
+	unsigned int s_mb_max_linear_groups;
 	unsigned int s_mb_stream_request;
 	unsigned int s_mb_max_to_scan;
 	unsigned int s_mb_min_to_scan;
@@ -1554,6 +1566,8 @@ struct ext4_sb_info {
 	atomic_t s_bal_goals;	/* goal hits */
 	atomic_t s_bal_breaks;	/* too long searches */
 	atomic_t s_bal_2orders;	/* 2^order hits */
+	atomic_t s_bal_cr0_bad_suggestions;
+	atomic_t s_bal_cr1_bad_suggestions;
 	atomic64_t s_bal_cX_groups_considered[4];
 	atomic64_t s_bal_cX_hits[4];
 	atomic64_t s_bal_cX_failed[4];		/* cX loop didn't find blocks */
@@ -3360,11 +3374,14 @@ struct ext4_group_info {
 	ext4_grpblk_t	bb_free;	/* total free blocks */
 	ext4_grpblk_t	bb_fragments;	/* nr of freespace fragments */
 	ext4_grpblk_t	bb_largest_free_order;/* order of largest frag in BG */
+	ext4_group_t	bb_group;	/* Group number */
 	struct          list_head bb_prealloc_list;
 #ifdef DOUBLE_CHECK
 	void            *bb_bitmap;
 #endif
 	struct rw_semaphore alloc_sem;
+	struct rb_node	bb_avg_fragment_size_rb;
+	struct list_head bb_largest_free_order_node;
 	ext4_grpblk_t	bb_counters[];	/* Nr of free power-of-two-block
 					 * regions, index is order.
 					 * bb_counters[3] = 5 means
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index e899a7d21982..c62555598a8e 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -127,11 +127,50 @@
  * smallest multiple of the stripe value (sbi->s_stripe) which is
  * greater than the default mb_group_prealloc.
  *
+ * If "mb_optimize_scan" mount option is set, we maintain in memory group info
+ * structures in two data structures:
+ *
+ * 1) Array of largest free order lists (sbi->s_mb_largest_free_orders)
+ *
+ *    Locking: sbi->s_mb_largest_free_orders_locks(array of rw locks)
+ *
+ *    This is an array of lists where the index in the array represents the
+ *    largest free order in the buddy bitmap of the participating group infos of
+ *    that list. So, there are exactly MB_NUM_ORDERS(sb) (which means total
+ *    number of buddy bitmap orders possible) number of lists. Group-infos are
+ *    placed in appropriate lists.
+ *
+ * 2) Average fragment size rb tree (sbi->s_mb_avg_fragment_size_root)
+ *
+ *    Locking: sbi->s_mb_rb_lock (rwlock)
+ *
+ *    This is a red black tree consisting of group infos and the tree is sorted
+ *    by average fragment sizes (which is calculated as ext4_group_info->bb_free
+ *    / ext4_group_info->bb_fragments).
+ *
+ * When "mb_optimize_scan" mount option is set, mballoc consults the above data
+ * structures to decide the order in which groups are to be traversed for
+ * fulfilling an allocation request.
+ *
+ * At CR = 0, we look for groups which have the largest_free_order >= the order
+ * of the request. We directly look at the largest free order list in the data
+ * structure (1) above where largest_free_order = order of the request. If that
+ * list is empty, we look at remaining list in the increasing order of
+ * largest_free_order. This allows us to perform CR = 0 lookup in O(1) time.
+ *
+ * At CR = 1, we only consider groups where average fragment size > request
+ * size. So, we lookup a group which has average fragment size just above or
+ * equal to request size using our rb tree (data structure 2) in O(log N) time.
+ *
+ * If "mb_optimize_scan" mount option is not set, mballoc traverses groups in
+ * linear order which requires O(N) search time for each CR 0 and CR 1 phase.
+ *
  * The regular allocator (using the buddy cache) supports a few tunables.
  *
  * /sys/fs/ext4/<partition>/mb_min_to_scan
  * /sys/fs/ext4/<partition>/mb_max_to_scan
  * /sys/fs/ext4/<partition>/mb_order2_req
+ * /sys/fs/ext4/<partition>/mb_linear_limit
  *
  * The regular allocator uses buddy scan only if the request len is power of
  * 2 blocks and the order of allocation is >= sbi->s_mb_order2_reqs. The
@@ -149,6 +188,16 @@
  * can be used for allocation. ext4_mb_good_group explains how the groups are
  * checked.
  *
+ * When "mb_optimize_scan" is turned on, as mentioned above, the groups may not
+ * get traversed linearly. That may result in subsequent allocations being not
+ * close to each other. And so, the underlying device may get filled up in a
+ * non-linear fashion. While that may not matter on non-rotational devices, for
+ * rotational devices that may result in higher seek times. "mb_linear_limit"
+ * tells mballoc how many groups mballoc should search linearly before
+ * performing consulting above data structures for more efficient lookups. For
+ * non rotational devices, this value defaults to 0 and for rotational devices
+ * this is set to MB_DEFAULT_LINEAR_LIMIT.
+ *
  * Both the prealloc space are getting populated as above. So for the first
  * request we will hit the buddy cache which will result in this prealloc
  * space getting filled. The prealloc space is then later used for the
@@ -299,6 +348,8 @@
  *  - bitlock on a group	(group)
  *  - object (inode/locality)	(object)
  *  - per-pa lock		(pa)
+ *  - cr0 lists lock		(cr0)
+ *  - cr1 tree lock		(cr1)
  *
  * Paths:
  *  - new pa
@@ -328,6 +379,9 @@
  *    group
  *        object
  *
+ *  - allocation path (ext4_mb_regular_allocator)
+ *    group
+ *    cr0/cr1
  */
 static struct kmem_cache *ext4_pspace_cachep;
 static struct kmem_cache *ext4_ac_cachep;
@@ -351,6 +405,9 @@ static void ext4_mb_generate_from_freelist(struct super_block *sb, void *bitmap,
 						ext4_group_t group);
 static void ext4_mb_new_preallocation(struct ext4_allocation_context *ac);
 
+static bool ext4_mb_good_group(struct ext4_allocation_context *ac,
+			       ext4_group_t group, int cr);
+
 /*
  * The algorithm using this percpu seq counter goes below:
  * 1. We sample the percpu discard_pa_seq counter before trying for block
@@ -744,6 +801,269 @@ static void ext4_mb_mark_free_simple(struct super_block *sb,
 	}
 }
 
+static void ext4_mb_rb_insert(struct rb_root *root, struct rb_node *new,
+			int (*cmp)(struct rb_node *, struct rb_node *))
+{
+	struct rb_node **iter = &root->rb_node, *parent = NULL;
+
+	while (*iter) {
+		parent = *iter;
+		if (cmp(new, *iter) > 0)
+			iter = &((*iter)->rb_left);
+		else
+			iter = &((*iter)->rb_right);
+	}
+
+	rb_link_node(new, parent, iter);
+	rb_insert_color(new, root);
+}
+
+static int
+ext4_mb_avg_fragment_size_cmp(struct rb_node *rb1, struct rb_node *rb2)
+{
+	struct ext4_group_info *grp1 = rb_entry(rb1,
+						struct ext4_group_info,
+						bb_avg_fragment_size_rb);
+	struct ext4_group_info *grp2 = rb_entry(rb2,
+						struct ext4_group_info,
+						bb_avg_fragment_size_rb);
+	int num_frags_1, num_frags_2;
+
+	num_frags_1 = grp1->bb_fragments ?
+		grp1->bb_free / grp1->bb_fragments : 0;
+	num_frags_2 = grp2->bb_fragments ?
+		grp2->bb_free / grp2->bb_fragments : 0;
+
+	return (num_frags_2 - num_frags_1);
+}
+
+/*
+ * Reinsert grpinfo into the avg_fragment_size tree with new average
+ * fragment size.
+ */
+static void
+mb_update_avg_fragment_size(struct super_block *sb, struct ext4_group_info *grp)
+{
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+
+	if (!test_opt2(sb, MB_OPTIMIZE_SCAN) || grp->bb_free == 0)
+		return;
+
+	write_lock(&sbi->s_mb_rb_lock);
+	if (!RB_EMPTY_NODE(&grp->bb_avg_fragment_size_rb)) {
+		rb_erase(&grp->bb_avg_fragment_size_rb,
+				&sbi->s_mb_avg_fragment_size_root);
+		RB_CLEAR_NODE(&grp->bb_avg_fragment_size_rb);
+	}
+
+	ext4_mb_rb_insert(&sbi->s_mb_avg_fragment_size_root,
+		&grp->bb_avg_fragment_size_rb,
+		ext4_mb_avg_fragment_size_cmp);
+	write_unlock(&sbi->s_mb_rb_lock);
+}
+
+/*
+ * Choose next group by traversing largest_free_order lists. Updates *new_cr if
+ * cr level needs an update.
+ */
+static void ext4_mb_choose_next_group_cr0(struct ext4_allocation_context *ac,
+			int *new_cr, ext4_group_t *group, ext4_group_t ngroups)
+{
+	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
+	struct ext4_group_info *iter, *grp;
+	int i;
+
+	if (ac->ac_status == AC_STATUS_FOUND)
+		return;
+
+	if (unlikely(sbi->s_mb_stats && ac->ac_flags & EXT4_MB_CR0_OPTIMIZED))
+		atomic_inc(&sbi->s_bal_cr0_bad_suggestions);
+
+	grp = NULL;
+	for (i = ac->ac_2order; i < MB_NUM_ORDERS(ac->ac_sb); i++) {
+		if (list_empty(&sbi->s_mb_largest_free_orders[i]))
+			continue;
+		read_lock(&sbi->s_mb_largest_free_orders_locks[i]);
+		if (list_empty(&sbi->s_mb_largest_free_orders[i])) {
+			read_unlock(&sbi->s_mb_largest_free_orders_locks[i]);
+			continue;
+		}
+		grp = NULL;
+		list_for_each_entry(iter, &sbi->s_mb_largest_free_orders[i],
+				    bb_largest_free_order_node) {
+			if (sbi->s_mb_stats)
+				atomic64_inc(&sbi->s_bal_cX_groups_considered[0]);
+			if (likely(ext4_mb_good_group(ac, iter->bb_group, 0))) {
+				grp = iter;
+				break;
+			}
+		}
+		read_unlock(&sbi->s_mb_largest_free_orders_locks[i]);
+		if (grp)
+			break;
+	}
+
+	if (!grp) {
+		/* Increment cr and search again */
+		*new_cr = 1;
+	} else {
+		*group = grp->bb_group;
+		ac->ac_last_optimal_group = *group;
+		ac->ac_flags |= EXT4_MB_CR0_OPTIMIZED;
+	}
+}
+
+/*
+ * Choose next group by traversing average fragment size tree. Updates *new_cr
+ * if cr lvel needs an update. Sets EXT4_MB_SEARCH_NEXT_LINEAR to indicate that
+ * the linear search should continue for one iteration since there's lock
+ * contention on the rb tree lock.
+ */
+static void ext4_mb_choose_next_group_cr1(struct ext4_allocation_context *ac,
+		int *new_cr, ext4_group_t *group, ext4_group_t ngroups)
+{
+	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
+	int avg_fragment_size, best_so_far;
+	struct rb_node *node, *found;
+	struct ext4_group_info *grp;
+
+	/*
+	 * If there is contention on the lock, instead of waiting for the lock
+	 * to become available, just continue searching lineraly. We'll resume
+	 * our rb tree search later starting at ac->ac_last_optimal_group.
+	 */
+	if (!read_trylock(&sbi->s_mb_rb_lock)) {
+		ac->ac_flags |= EXT4_MB_SEARCH_NEXT_LINEAR;
+		return;
+	}
+
+	if (unlikely(ac->ac_flags & EXT4_MB_CR1_OPTIMIZED)) {
+		if (sbi->s_mb_stats)
+			atomic_inc(&sbi->s_bal_cr1_bad_suggestions);
+		/* We have found something at CR 1 in the past */
+		grp = ext4_get_group_info(ac->ac_sb, ac->ac_last_optimal_group);
+		for (found = rb_next(&grp->bb_avg_fragment_size_rb); found != NULL;
+		     found = rb_next(found)) {
+			grp = rb_entry(found, struct ext4_group_info,
+				       bb_avg_fragment_size_rb);
+			if (sbi->s_mb_stats)
+				atomic64_inc(&sbi->s_bal_cX_groups_considered[1]);
+			if (likely(ext4_mb_good_group(ac, grp->bb_group, 1)))
+				break;
+		}
+		goto done;
+	}
+
+	node = sbi->s_mb_avg_fragment_size_root.rb_node;
+	best_so_far = 0;
+	found = NULL;
+
+	while (node) {
+		grp = rb_entry(node, struct ext4_group_info,
+			       bb_avg_fragment_size_rb);
+		avg_fragment_size = 0;
+		if (ext4_mb_good_group(ac, grp->bb_group, 1)) {
+			avg_fragment_size = grp->bb_fragments ?
+				grp->bb_free / grp->bb_fragments : 0;
+			if (!best_so_far || avg_fragment_size < best_so_far) {
+				best_so_far = avg_fragment_size;
+				found = node;
+			}
+		}
+		if (avg_fragment_size > ac->ac_g_ex.fe_len)
+			node = node->rb_right;
+		else
+			node = node->rb_left;
+	}
+
+done:
+	if (found) {
+		grp = rb_entry(found, struct ext4_group_info,
+			       bb_avg_fragment_size_rb);
+		*group = grp->bb_group;
+		ac->ac_flags |= EXT4_MB_CR1_OPTIMIZED;
+	} else {
+		*new_cr = 2;
+	}
+
+	read_unlock(&sbi->s_mb_rb_lock);
+	ac->ac_last_optimal_group = *group;
+}
+
+static inline int should_optimize_scan(struct ext4_allocation_context *ac)
+{
+	if (unlikely(!test_opt2(ac->ac_sb, MB_OPTIMIZE_SCAN)))
+		return 0;
+	if (ac->ac_criteria >= 2)
+		return 0;
+	if (ext4_test_inode_flag(ac->ac_inode, EXT4_INODE_EXTENTS))
+		return 0;
+	return 1;
+}
+
+/*
+ * Return next linear group for allocation. If linear traversal should not be
+ * performed, this function just returns the same group
+ */
+static int
+next_linear_group(struct ext4_allocation_context *ac, int group, int ngroups)
+{
+	if (!should_optimize_scan(ac))
+		goto inc_and_return;
+
+	if (ac->ac_groups_linear_remaining) {
+		ac->ac_groups_linear_remaining--;
+		goto inc_and_return;
+	}
+
+	if (ac->ac_flags & EXT4_MB_SEARCH_NEXT_LINEAR) {
+		ac->ac_flags &= ~EXT4_MB_SEARCH_NEXT_LINEAR;
+		goto inc_and_return;
+	}
+
+	return group;
+inc_and_return:
+	/*
+	 * Artificially restricted ngroups for non-extent
+	 * files makes group > ngroups possible on first loop.
+	 */
+	return group + 1 >= ngroups ? 0 : group + 1;
+}
+
+/*
+ * ext4_mb_choose_next_group: choose next group for allocation.
+ *
+ * @ac        Allocation Context
+ * @new_cr    This is an output parameter. If the there is no good group
+ *            available at current CR level, this field is updated to indicate
+ *            the new cr level that should be used.
+ * @group     This is an input / output parameter. As an input it indicates the
+ *            next group that the allocator intends to use for allocation. As
+ *            output, this field indicates the next group that should be used as
+ *            determined by the optimization functions.
+ * @ngroups   Total number of groups
+ */
+static void ext4_mb_choose_next_group(struct ext4_allocation_context *ac,
+		int *new_cr, ext4_group_t *group, ext4_group_t ngroups)
+{
+	*new_cr = ac->ac_criteria;
+
+	if (!should_optimize_scan(ac) || ac->ac_groups_linear_remaining)
+		return;
+
+	if (*new_cr == 0) {
+		ext4_mb_choose_next_group_cr0(ac, new_cr, group, ngroups);
+	} else if (*new_cr == 1) {
+		ext4_mb_choose_next_group_cr1(ac, new_cr, group, ngroups);
+	} else {
+		/*
+		 * TODO: For CR=2, we can arrange groups in an rb tree sorted by
+		 * bb_free. But until that happens, we should never come here.
+		 */
+		WARN_ON(1);
+	}
+}
+
 /*
  * Cache the order of the largest free extent we have available in this block
  * group.
@@ -751,18 +1071,33 @@ static void ext4_mb_mark_free_simple(struct super_block *sb,
 static void
 mb_set_largest_free_order(struct super_block *sb, struct ext4_group_info *grp)
 {
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
 	int i;
-	int bits;
 
+	if (test_opt2(sb, MB_OPTIMIZE_SCAN) && grp->bb_largest_free_order >= 0) {
+		write_lock(&sbi->s_mb_largest_free_orders_locks[
+					      grp->bb_largest_free_order]);
+		list_del_init(&grp->bb_largest_free_order_node);
+		write_unlock(&sbi->s_mb_largest_free_orders_locks[
+					      grp->bb_largest_free_order]);
+	}
 	grp->bb_largest_free_order = -1; /* uninit */
 
-	bits = MB_NUM_ORDERS(sb) - 1;
-	for (i = bits; i >= 0; i--) {
+	for (i = MB_NUM_ORDERS(sb) - 1; i >= 0; i--) {
 		if (grp->bb_counters[i] > 0) {
 			grp->bb_largest_free_order = i;
 			break;
 		}
 	}
+	if (test_opt2(sb, MB_OPTIMIZE_SCAN) &&
+	    grp->bb_largest_free_order >= 0 && grp->bb_free) {
+		write_lock(&sbi->s_mb_largest_free_orders_locks[
+					      grp->bb_largest_free_order]);
+		list_add_tail(&grp->bb_largest_free_order_node,
+		      &sbi->s_mb_largest_free_orders[grp->bb_largest_free_order]);
+		write_unlock(&sbi->s_mb_largest_free_orders_locks[
+					      grp->bb_largest_free_order]);
+	}
 }
 
 static noinline_for_stack
@@ -818,6 +1153,7 @@ void ext4_mb_generate_buddy(struct super_block *sb,
 	period = get_cycles() - period;
 	atomic_inc(&sbi->s_mb_buddies_generated);
 	atomic64_add(period, &sbi->s_mb_generation_time);
+	mb_update_avg_fragment_size(sb, grp);
 }
 
 /* The buddy information is attached the buddy cache inode
@@ -1517,6 +1853,7 @@ static void mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b,
 
 done:
 	mb_set_largest_free_order(sb, e4b->bd_info);
+	mb_update_avg_fragment_size(sb, e4b->bd_info);
 	mb_check_buddy(e4b);
 }
 
@@ -1653,6 +1990,7 @@ static int mb_mark_used(struct ext4_buddy *e4b, struct ext4_free_extent *ex)
 	}
 	mb_set_largest_free_order(e4b->bd_sb, e4b->bd_info);
 
+	mb_update_avg_fragment_size(e4b->bd_sb, e4b->bd_info);
 	ext4_set_bits(e4b->bd_bitmap, ex->fe_start, len0);
 	mb_check_buddy(e4b);
 
@@ -2347,17 +2685,21 @@ repeat:
 		 * from the goal value specified
 		 */
 		group = ac->ac_g_ex.fe_group;
+		ac->ac_last_optimal_group = group;
+		ac->ac_groups_linear_remaining = sbi->s_mb_max_linear_groups;
 		prefetch_grp = group;
 
-		for (i = 0; i < ngroups; group++, i++) {
-			int ret = 0;
+		for (i = 0; i < ngroups; group = next_linear_group(ac, group, ngroups),
+			     i++) {
+			int ret = 0, new_cr;
+
 			cond_resched();
-			/*
-			 * Artificially restricted ngroups for non-extent
-			 * files makes group > ngroups possible on first loop.
-			 */
-			if (group >= ngroups)
-				group = 0;
+
+			ext4_mb_choose_next_group(ac, &new_cr, &group, ngroups);
+			if (new_cr != cr) {
+				cr = new_cr;
+				goto repeat;
+			}
 
 			/*
 			 * Batch reads of the block allocation bitmaps
@@ -2578,6 +2920,8 @@ int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
 		   atomic64_read(&sbi->s_bal_cX_groups_considered[0]));
 	seq_printf(seq, "\t\tuseless_loops: %llu\n",
 		   atomic64_read(&sbi->s_bal_cX_failed[0]));
+	seq_printf(seq, "\t\tbad_suggestions: %u\n",
+		   atomic_read(&sbi->s_bal_cr0_bad_suggestions));
 
 	seq_puts(seq, "\tcr1_stats:\n");
 	seq_printf(seq, "\t\thits: %llu\n", atomic64_read(&sbi->s_bal_cX_hits[1]));
@@ -2585,6 +2929,8 @@ int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
 		   atomic64_read(&sbi->s_bal_cX_groups_considered[1]));
 	seq_printf(seq, "\t\tuseless_loops: %llu\n",
 		   atomic64_read(&sbi->s_bal_cX_failed[1]));
+	seq_printf(seq, "\t\tbad_suggestions: %u\n",
+		   atomic_read(&sbi->s_bal_cr1_bad_suggestions));
 
 	seq_puts(seq, "\tcr2_stats:\n");
 	seq_printf(seq, "\t\thits: %llu\n", atomic64_read(&sbi->s_bal_cX_hits[2]));
@@ -2719,7 +3065,10 @@ int ext4_mb_add_groupinfo(struct super_block *sb, ext4_group_t group,
 	INIT_LIST_HEAD(&meta_group_info[i]->bb_prealloc_list);
 	init_rwsem(&meta_group_info[i]->alloc_sem);
 	meta_group_info[i]->bb_free_root = RB_ROOT;
+	INIT_LIST_HEAD(&meta_group_info[i]->bb_largest_free_order_node);
+	RB_CLEAR_NODE(&meta_group_info[i]->bb_avg_fragment_size_rb);
 	meta_group_info[i]->bb_largest_free_order = -1;  /* uninit */
+	meta_group_info[i]->bb_group = group;
 
 	mb_group_bb_bitmap_alloc(sb, meta_group_info[i], group);
 	return 0;
@@ -2916,6 +3265,26 @@ int ext4_mb_init(struct super_block *sb)
 		i++;
 	} while (i < MB_NUM_ORDERS(sb));
 
+	sbi->s_mb_avg_fragment_size_root = RB_ROOT;
+	sbi->s_mb_largest_free_orders =
+		kmalloc_array(MB_NUM_ORDERS(sb), sizeof(struct list_head),
+			GFP_KERNEL);
+	if (!sbi->s_mb_largest_free_orders) {
+		ret = -ENOMEM;
+		goto out;
+	}
+	sbi->s_mb_largest_free_orders_locks =
+		kmalloc_array(MB_NUM_ORDERS(sb), sizeof(rwlock_t),
+			GFP_KERNEL);
+	if (!sbi->s_mb_largest_free_orders_locks) {
+		ret = -ENOMEM;
+		goto out;
+	}
+	for (i = 0; i < MB_NUM_ORDERS(sb); i++) {
+		INIT_LIST_HEAD(&sbi->s_mb_largest_free_orders[i]);
+		rwlock_init(&sbi->s_mb_largest_free_orders_locks[i]);
+	}
+	rwlock_init(&sbi->s_mb_rb_lock);
 
 	spin_lock_init(&sbi->s_md_lock);
 	sbi->s_mb_free_pending = 0;
@@ -2968,6 +3337,10 @@ int ext4_mb_init(struct super_block *sb)
 		spin_lock_init(&lg->lg_prealloc_lock);
 	}
 
+	if (blk_queue_nonrot(bdev_get_queue(sb->s_bdev)))
+		sbi->s_mb_max_linear_groups = 0;
+	else
+		sbi->s_mb_max_linear_groups = MB_DEFAULT_LINEAR_LIMIT;
 	/* init file for buddy data */
 	ret = ext4_mb_init_backend(sb);
 	if (ret != 0)
@@ -2979,6 +3352,8 @@ out_free_locality_groups:
 	free_percpu(sbi->s_locality_groups);
 	sbi->s_locality_groups = NULL;
 out:
+	kfree(sbi->s_mb_largest_free_orders);
+	kfree(sbi->s_mb_largest_free_orders_locks);
 	kfree(sbi->s_mb_offsets);
 	sbi->s_mb_offsets = NULL;
 	kfree(sbi->s_mb_maxs);
@@ -3035,6 +3410,8 @@ int ext4_mb_release(struct super_block *sb)
 		kvfree(group_info);
 		rcu_read_unlock();
 	}
+	kfree(sbi->s_mb_largest_free_orders);
+	kfree(sbi->s_mb_largest_free_orders_locks);
 	kfree(sbi->s_mb_offsets);
 	kfree(sbi->s_mb_maxs);
 	iput(sbi->s_buddy_cache);
diff --git a/fs/ext4/mballoc.h b/fs/ext4/mballoc.h
index 68111a10cfee..02585e3cbcad 100644
--- a/fs/ext4/mballoc.h
+++ b/fs/ext4/mballoc.h
@@ -79,6 +79,18 @@
 #define MB_DEFAULT_MAX_INODE_PREALLOC	512
 
 /*
+ * Number of groups to search linearly before performing group scanning
+ * optimization.
+ */
+#define MB_DEFAULT_LINEAR_LIMIT		4
+
+/*
+ * Minimum number of groups that should be present in the file system to perform
+ * group scanning optimizations.
+ */
+#define MB_DEFAULT_LINEAR_SCAN_THRESHOLD	16
+
+/*
  * Number of valid buddy orders
  */
 #define MB_NUM_ORDERS(sb)		((sb)->s_blocksize_bits + 2)
@@ -166,11 +178,14 @@ struct ext4_allocation_context {
 	/* copy of the best found extent taken before preallocation efforts */
 	struct ext4_free_extent ac_f_ex;
 
+	ext4_group_t ac_last_optimal_group;
+	__u32 ac_groups_considered;
+	__u32 ac_flags;		/* allocation hints */
 	__u16 ac_groups_scanned;
+	__u16 ac_groups_linear_remaining;
 	__u16 ac_found;
 	__u16 ac_tail;
 	__u16 ac_buddy;
-	__u16 ac_flags;		/* allocation hints */
 	__u8 ac_status;
 	__u8 ac_criteria;
 	__u8 ac_2order;		/* if request is to allocate 2^N blocks and
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 0ef82e646100..3b12deb93a6b 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1688,7 +1688,7 @@ enum {
 	Opt_dioread_nolock, Opt_dioread_lock,
 	Opt_discard, Opt_nodiscard, Opt_init_itable, Opt_noinit_itable,
 	Opt_max_dir_size_kb, Opt_nojournal_checksum, Opt_nombcache,
-	Opt_prefetch_block_bitmaps,
+	Opt_prefetch_block_bitmaps, Opt_mb_optimize_scan,
 #ifdef CONFIG_EXT4_DEBUG
 	Opt_fc_debug_max_replay, Opt_fc_debug_force
 #endif
@@ -1789,6 +1789,7 @@ static const match_table_t tokens = {
 	{Opt_nombcache, "nombcache"},
 	{Opt_nombcache, "no_mbcache"},	/* for backward compatibility */
 	{Opt_prefetch_block_bitmaps, "prefetch_block_bitmaps"},
+	{Opt_mb_optimize_scan, "mb_optimize_scan=%d"},
 	{Opt_removed, "check=none"},	/* mount option from ext2/3 */
 	{Opt_removed, "nocheck"},	/* mount option from ext2/3 */
 	{Opt_removed, "reservation"},	/* mount option from ext2/3 */
@@ -1821,6 +1822,8 @@ static ext4_fsblk_t get_sb_block(void **data)
 }
 
 #define DEFAULT_JOURNAL_IOPRIO (IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, 3))
+#define DEFAULT_MB_OPTIMIZE_SCAN	(-1)
+
 static const char deprecated_msg[] =
 	"Mount option \"%s\" will be removed by %s\n"
 	"Contact linux-ext4@vger.kernel.org if you think we should keep it.\n";
@@ -2009,6 +2012,7 @@ static const struct mount_opts {
 	{Opt_nombcache, EXT4_MOUNT_NO_MBCACHE, MOPT_SET},
 	{Opt_prefetch_block_bitmaps, EXT4_MOUNT_PREFETCH_BLOCK_BITMAPS,
 	 MOPT_SET},
+	{Opt_mb_optimize_scan, EXT4_MOUNT2_MB_OPTIMIZE_SCAN, MOPT_GTE0},
 #ifdef CONFIG_EXT4_DEBUG
 	{Opt_fc_debug_force, EXT4_MOUNT2_JOURNAL_FAST_COMMIT,
 	 MOPT_SET | MOPT_2 | MOPT_EXT4_ONLY},
@@ -2093,6 +2097,7 @@ static int ext4_set_test_dummy_encryption(struct super_block *sb,
 struct ext4_parsed_options {
 	unsigned long journal_devnum;
 	unsigned int journal_ioprio;
+	int mb_optimize_scan;
 };
 
 static int handle_mount_opt(struct super_block *sb, char *opt, int token,
@@ -2389,6 +2394,13 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token,
 		sbi->s_mount_opt |= m->mount_opt;
 	} else if (token == Opt_data_err_ignore) {
 		sbi->s_mount_opt &= ~m->mount_opt;
+	} else if (token == Opt_mb_optimize_scan) {
+		if (arg != 0 && arg != 1) {
+			ext4_msg(sb, KERN_WARNING,
+				 "mb_optimize_scan should be set to 0 or 1.");
+			return -1;
+		}
+		parsed_opts->mb_optimize_scan = arg;
 	} else {
 		if (!args->from)
 			arg = 1;
@@ -4035,6 +4047,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	/* Set defaults for the variables that will be set during parsing */
 	parsed_opts.journal_ioprio = DEFAULT_JOURNAL_IOPRIO;
 	parsed_opts.journal_devnum = 0;
+	parsed_opts.mb_optimize_scan = DEFAULT_MB_OPTIMIZE_SCAN;
 
 	if ((data && !orig_data) || !sbi)
 		goto out_free_base;
@@ -4979,6 +4992,19 @@ no_journal:
 	ext4_fc_replay_cleanup(sb);
 
 	ext4_ext_init(sb);
+
+	/*
+	 * Enable optimize_scan if number of groups is > threshold. This can be
+	 * turned off by passing "mb_optimize_scan=0". This can also be
+	 * turned on forcefully by passing "mb_optimize_scan=1".
+	 */
+	if (parsed_opts.mb_optimize_scan == 1)
+		set_opt2(sb, MB_OPTIMIZE_SCAN);
+	else if (parsed_opts.mb_optimize_scan == 0)
+		clear_opt2(sb, MB_OPTIMIZE_SCAN);
+	else if (sbi->s_groups_count >= MB_DEFAULT_LINEAR_SCAN_THRESHOLD)
+		set_opt2(sb, MB_OPTIMIZE_SCAN);
+
 	err = ext4_mb_init(sb);
 	if (err) {
 		ext4_msg(sb, KERN_ERR, "failed to initialize mballoc (%d)",
diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
index 1b5580eb88e6..8716790e7e21 100644
--- a/fs/ext4/sysfs.c
+++ b/fs/ext4/sysfs.c
@@ -215,6 +215,7 @@ EXT4_RW_ATTR_SBI_UI(mb_order2_req, s_mb_order2_reqs);
 EXT4_RW_ATTR_SBI_UI(mb_stream_req, s_mb_stream_request);
 EXT4_RW_ATTR_SBI_UI(mb_group_prealloc, s_mb_group_prealloc);
 EXT4_RW_ATTR_SBI_UI(mb_max_inode_prealloc, s_mb_max_inode_prealloc);
+EXT4_RW_ATTR_SBI_UI(mb_max_linear_groups, s_mb_max_linear_groups);
 EXT4_RW_ATTR_SBI_UI(extent_max_zeroout_kb, s_extent_max_zeroout_kb);
 EXT4_ATTR(trigger_fs_error, 0200, trigger_test_error);
 EXT4_RW_ATTR_SBI_UI(err_ratelimit_interval_ms, s_err_ratelimit_state.interval);
@@ -263,6 +264,7 @@ static struct attribute *ext4_attrs[] = {
 	ATTR_LIST(mb_stream_req),
 	ATTR_LIST(mb_group_prealloc),
 	ATTR_LIST(mb_max_inode_prealloc),
+	ATTR_LIST(mb_max_linear_groups),
 	ATTR_LIST(max_writeback_mb_bump),
 	ATTR_LIST(extent_max_zeroout_kb),
 	ATTR_LIST(trigger_fs_error),