btrfs: zoned: track unusable bytes for zones

In a zoned filesystem a once written then freed region is not usable
until the underlying zone has been reset. So we need to distinguish such
unusable space from usable free space.

Therefore we need to introduce the "zone_unusable" field to the block
group structure, and "bytes_zone_unusable" to the space_info structure
to track the unusable space.

Pinned bytes are always reclaimed to the unusable space. But, when an
allocated region is returned before using e.g., the block group becomes
read-only between allocation time and reservation time, we can safely
return the region to the block group. For the situation, this commit
introduces "btrfs_add_free_space_unused". This behaves the same as
btrfs_add_free_space() on regular filesystem. On zoned filesystems, it
rewinds the allocation offset.

Because the read-only bytes tracks free but unusable bytes when the block
group is read-only, we need to migrate the zone_unusable bytes to
read-only bytes when a block group is marked read-only.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/block-group.c

@@ -1009,12 +1009,17 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
 		WARN_ON(block_group->space_info->total_bytes
 			< block_group->length);
 		WARN_ON(block_group->space_info->bytes_readonly
-			< block_group->length);
+			< block_group->length - block_group->zone_unusable);
+		WARN_ON(block_group->space_info->bytes_zone_unusable
+			< block_group->zone_unusable);
 		WARN_ON(block_group->space_info->disk_total
 			< block_group->length * factor);
 	}
 	block_group->space_info->total_bytes -= block_group->length;
-	block_group->space_info->bytes_readonly -= block_group->length;
+	block_group->space_info->bytes_readonly -=
+		(block_group->length - block_group->zone_unusable);
+	block_group->space_info->bytes_zone_unusable -=
+		block_group->zone_unusable;
 	block_group->space_info->disk_total -= block_group->length * factor;
 
 	spin_unlock(&block_group->space_info->lock);
@@ -1158,7 +1163,7 @@ static int inc_block_group_ro(struct btrfs_block_group *cache, int force)
 	}
 
 	num_bytes = cache->length - cache->reserved - cache->pinned -
-		    cache->bytes_super - cache->used;
+		    cache->bytes_super - cache->zone_unusable - cache->used;
 
 	/*
 	 * Data never overcommits, even in mixed mode, so do just the straight
@@ -1189,6 +1194,12 @@ static int inc_block_group_ro(struct btrfs_block_group *cache, int force)
 
 	if (!ret) {
 		sinfo->bytes_readonly += num_bytes;
+		if (btrfs_is_zoned(cache->fs_info)) {
+			/* Migrate zone_unusable bytes to readonly */
+			sinfo->bytes_readonly += cache->zone_unusable;
+			sinfo->bytes_zone_unusable -= cache->zone_unusable;
+			cache->zone_unusable = 0;
+		}
 		cache->ro++;
 		list_add_tail(&cache->ro_list, &sinfo->ro_bgs);
 	}
@@ -1876,12 +1887,20 @@ static int read_one_block_group(struct btrfs_fs_info *info,
 	}
 
 	/*
-	 * Check for two cases, either we are full, and therefore don't need
-	 * to bother with the caching work since we won't find any space, or we
-	 * are empty, and we can just add all the space in and be done with it.
-	 * This saves us _a_lot_ of time, particularly in the full case.
-	 */
-	if (cache->length == cache->used) {
+	 * For zoned filesystem, space after the allocation offset is the only
+	 * free space for a block group. So, we don't need any caching work.
+	 * btrfs_calc_zone_unusable() will set the amount of free space and
+	 * zone_unusable space.
+	 *
+	 * For regular filesystem, check for two cases, either we are full, and
+	 * therefore don't need to bother with the caching work since we won't
+	 * find any space, or we are empty, and we can just add all the space
+	 * in and be done with it.  This saves us _a_lot_ of time, particularly
+	 * in the full case.
+	 */
+	if (btrfs_is_zoned(info)) {
+		btrfs_calc_zone_unusable(cache);
+	} else if (cache->length == cache->used) {
 		cache->last_byte_to_unpin = (u64)-1;
 		cache->cached = BTRFS_CACHE_FINISHED;
 		btrfs_free_excluded_extents(cache);
@@ -1900,7 +1919,8 @@ static int read_one_block_group(struct btrfs_fs_info *info,
 	}
 	trace_btrfs_add_block_group(info, cache, 0);
 	btrfs_update_space_info(info, cache->flags, cache->length,
-				cache->used, cache->bytes_super, &space_info);
+				cache->used, cache->bytes_super,
+				cache->zone_unusable, &space_info);
 
 	cache->space_info = space_info;
 
@@ -1956,7 +1976,7 @@ static int fill_dummy_bgs(struct btrfs_fs_info *fs_info)
 			break;
 		}
 		btrfs_update_space_info(fs_info, bg->flags, em->len, em->len,
-					0, &space_info);
+					0, 0, &space_info);
 		bg->space_info = space_info;
 		link_block_group(bg);
 
@@ -2197,7 +2217,7 @@ int btrfs_make_block_group(struct btrfs_trans_handle *trans, u64 bytes_used,
 	 */
 	trace_btrfs_add_block_group(fs_info, cache, 1);
 	btrfs_update_space_info(fs_info, cache->flags, size, bytes_used,
-				cache->bytes_super, &cache->space_info);
+				cache->bytes_super, 0, &cache->space_info);
 	btrfs_update_global_block_rsv(fs_info);
 
 	link_block_group(cache);
@@ -2305,8 +2325,15 @@ void btrfs_dec_block_group_ro(struct btrfs_block_group *cache)
 	spin_lock(&cache->lock);
 	if (!--cache->ro) {
 		num_bytes = cache->length - cache->reserved -
-			    cache->pinned - cache->bytes_super - cache->used;
+			    cache->pinned - cache->bytes_super -
+			    cache->zone_unusable - cache->used;
 		sinfo->bytes_readonly -= num_bytes;
+		if (btrfs_is_zoned(cache->fs_info)) {
+			/* Migrate zone_unusable bytes back */
+			cache->zone_unusable = cache->alloc_offset - cache->used;
+			sinfo->bytes_zone_unusable += cache->zone_unusable;
+			sinfo->bytes_readonly -= cache->zone_unusable;
+		}
 		list_del_init(&cache->ro_list);
 	}
 	spin_unlock(&cache->lock);

fs/btrfs/block-group.h

@@ -189,6 +189,7 @@ struct btrfs_block_group {
 	 * allocation. This is used only on a zoned filesystem.
 	 */
 	u64 alloc_offset;
+	u64 zone_unusable;
 };
 
 static inline u64 btrfs_block_group_end(struct btrfs_block_group *block_group)

fs/btrfs/extent-tree.c

@@ -34,6 +34,7 @@
 #include "block-group.h"
 #include "discard.h"
 #include "rcu-string.h"
+#include "zoned.h"
 
 #undef SCRAMBLE_DELAYED_REFS
 
@@ -2740,6 +2741,10 @@ static int unpin_extent_range(struct btrfs_fs_info *fs_info,
 		if (cache->ro) {
 			space_info->bytes_readonly += len;
 			readonly = true;
+		} else if (btrfs_is_zoned(fs_info)) {
+			/* Need reset before reusing in a zoned block group */
+			space_info->bytes_zone_unusable += len;
+			readonly = true;
 		}
 		spin_unlock(&cache->lock);
 		if (!readonly && return_free_space &&

fs/btrfs/free-space-cache.c

@@ -2477,6 +2477,8 @@ int __btrfs_add_free_space(struct btrfs_fs_info *fs_info,
 	int ret = 0;
 	u64 filter_bytes = bytes;
 
+	ASSERT(!btrfs_is_zoned(fs_info));
+
 	info = kmem_cache_zalloc(btrfs_free_space_cachep, GFP_NOFS);
 	if (!info)
 		return -ENOMEM;
@@ -2534,11 +2536,49 @@ int __btrfs_add_free_space(struct btrfs_fs_info *fs_info,
 	return ret;
 }
 
+static int __btrfs_add_free_space_zoned(struct btrfs_block_group *block_group,
+					u64 bytenr, u64 size, bool used)
+{
+	struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
+	u64 offset = bytenr - block_group->start;
+	u64 to_free, to_unusable;
+
+	spin_lock(&ctl->tree_lock);
+	if (!used)
+		to_free = size;
+	else if (offset >= block_group->alloc_offset)
+		to_free = size;
+	else if (offset + size <= block_group->alloc_offset)
+		to_free = 0;
+	else
+		to_free = offset + size - block_group->alloc_offset;
+	to_unusable = size - to_free;
+
+	ctl->free_space += to_free;
+	block_group->zone_unusable += to_unusable;
+	spin_unlock(&ctl->tree_lock);
+	if (!used) {
+		spin_lock(&block_group->lock);
+		block_group->alloc_offset -= size;
+		spin_unlock(&block_group->lock);
+	}
+
+	/* All the region is now unusable. Mark it as unused and reclaim */
+	if (block_group->zone_unusable == block_group->length)
+		btrfs_mark_bg_unused(block_group);
+
+	return 0;
+}
+
 int btrfs_add_free_space(struct btrfs_block_group *block_group,
 			 u64 bytenr, u64 size)
 {
 	enum btrfs_trim_state trim_state = BTRFS_TRIM_STATE_UNTRIMMED;
 
+	if (btrfs_is_zoned(block_group->fs_info))
+		return __btrfs_add_free_space_zoned(block_group, bytenr, size,
+						    true);
+
 	if (btrfs_test_opt(block_group->fs_info, DISCARD_SYNC))
 		trim_state = BTRFS_TRIM_STATE_TRIMMED;
 
@@ -2547,6 +2587,16 @@ int btrfs_add_free_space(struct btrfs_block_group *block_group,
 				      bytenr, size, trim_state);
 }
 
+int btrfs_add_free_space_unused(struct btrfs_block_group *block_group,
+				u64 bytenr, u64 size)
+{
+	if (btrfs_is_zoned(block_group->fs_info))
+		return __btrfs_add_free_space_zoned(block_group, bytenr, size,
+						    false);
+
+	return btrfs_add_free_space(block_group, bytenr, size);
+}
+
 /*
  * This is a subtle distinction because when adding free space back in general,
  * we want it to be added as untrimmed for async. But in the case where we add
@@ -2557,6 +2607,10 @@ int btrfs_add_free_space_async_trimmed(struct btrfs_block_group *block_group,
 {
 	enum btrfs_trim_state trim_state = BTRFS_TRIM_STATE_UNTRIMMED;
 
+	if (btrfs_is_zoned(block_group->fs_info))
+		return __btrfs_add_free_space_zoned(block_group, bytenr, size,
+						    true);
+
 	if (btrfs_test_opt(block_group->fs_info, DISCARD_SYNC) ||
 	    btrfs_test_opt(block_group->fs_info, DISCARD_ASYNC))
 		trim_state = BTRFS_TRIM_STATE_TRIMMED;
@@ -2574,6 +2628,9 @@ int btrfs_remove_free_space(struct btrfs_block_group *block_group,
 	int ret;
 	bool re_search = false;
 
+	if (btrfs_is_zoned(block_group->fs_info))
+		return 0;
+
 	spin_lock(&ctl->tree_lock);
 
 again:
@@ -2668,6 +2725,16 @@ void btrfs_dump_free_space(struct btrfs_block_group *block_group,
 	struct rb_node *n;
 	int count = 0;
 
+	/*
+	 * Zoned btrfs does not use free space tree and cluster. Just print
+	 * out the free space after the allocation offset.
+	 */
+	if (btrfs_is_zoned(fs_info)) {
+		btrfs_info(fs_info, "free space %llu",
+			   block_group->length - block_group->alloc_offset);
+		return;
+	}
+
 	spin_lock(&ctl->tree_lock);
 	for (n = rb_first(&ctl->free_space_offset); n; n = rb_next(n)) {
 		info = rb_entry(n, struct btrfs_free_space, offset_index);

fs/btrfs/free-space-cache.h

@@ -107,6 +107,8 @@ int __btrfs_add_free_space(struct btrfs_fs_info *fs_info,
 			   enum btrfs_trim_state trim_state);
 int btrfs_add_free_space(struct btrfs_block_group *block_group,
 			 u64 bytenr, u64 size);
+int btrfs_add_free_space_unused(struct btrfs_block_group *block_group,
+				u64 bytenr, u64 size);
 int btrfs_add_free_space_async_trimmed(struct btrfs_block_group *block_group,
 				       u64 bytenr, u64 size);
 int btrfs_remove_free_space(struct btrfs_block_group *block_group,

fs/btrfs/space-info.c

@@ -169,6 +169,7 @@ u64 __pure btrfs_space_info_used(struct btrfs_space_info *s_info,
 	ASSERT(s_info);
 	return s_info->bytes_used + s_info->bytes_reserved +
 		s_info->bytes_pinned + s_info->bytes_readonly +
+		s_info->bytes_zone_unusable +
 		(may_use_included ? s_info->bytes_may_use : 0);
 }
 
@@ -264,7 +265,7 @@ int btrfs_init_space_info(struct btrfs_fs_info *fs_info)
 
 void btrfs_update_space_info(struct btrfs_fs_info *info, u64 flags,
 			     u64 total_bytes, u64 bytes_used,
-			     u64 bytes_readonly,
+			     u64 bytes_readonly, u64 bytes_zone_unusable,
 			     struct btrfs_space_info **space_info)
 {
 	struct btrfs_space_info *found;
@@ -280,6 +281,7 @@ void btrfs_update_space_info(struct btrfs_fs_info *info, u64 flags,
 	found->bytes_used += bytes_used;
 	found->disk_used += bytes_used * factor;
 	found->bytes_readonly += bytes_readonly;
+	found->bytes_zone_unusable += bytes_zone_unusable;
 	if (total_bytes > 0)
 		found->full = 0;
 	btrfs_try_granting_tickets(info, found);
@@ -429,10 +431,10 @@ static void __btrfs_dump_space_info(struct btrfs_fs_info *fs_info,
 		   info->total_bytes - btrfs_space_info_used(info, true),
 		   info->full ? "" : "not ");
 	btrfs_info(fs_info,
-		"space_info total=%llu, used=%llu, pinned=%llu, reserved=%llu, may_use=%llu, readonly=%llu",
+		"space_info total=%llu, used=%llu, pinned=%llu, reserved=%llu, may_use=%llu, readonly=%llu zone_unusable=%llu",
 		info->total_bytes, info->bytes_used, info->bytes_pinned,
 		info->bytes_reserved, info->bytes_may_use,
-		info->bytes_readonly);
+		info->bytes_readonly, info->bytes_zone_unusable);
 
 	DUMP_BLOCK_RSV(fs_info, global_block_rsv);
 	DUMP_BLOCK_RSV(fs_info, trans_block_rsv);
@@ -461,9 +463,10 @@ void btrfs_dump_space_info(struct btrfs_fs_info *fs_info,
 	list_for_each_entry(cache, &info->block_groups[index], list) {
 		spin_lock(&cache->lock);
 		btrfs_info(fs_info,
-			"block group %llu has %llu bytes, %llu used %llu pinned %llu reserved %s",
+			"block group %llu has %llu bytes, %llu used %llu pinned %llu reserved %llu zone_unusable %s",
 			cache->start, cache->length, cache->used, cache->pinned,
-			cache->reserved, cache->ro ? "[readonly]" : "");
+			cache->reserved, cache->zone_unusable,
+			cache->ro ? "[readonly]" : "");
 		spin_unlock(&cache->lock);
 		btrfs_dump_free_space(cache, bytes);
 	}

fs/btrfs/space-info.h

@@ -17,6 +17,8 @@ struct btrfs_space_info {
 	u64 bytes_may_use;	/* number of bytes that may be used for
 				   delalloc/allocations */
 	u64 bytes_readonly;	/* total bytes that are read only */
+	u64 bytes_zone_unusable;	/* total bytes that are unusable until
+					   resetting the device zone */
 
 	u64 max_extent_size;	/* This will hold the maximum extent size of
 				   the space info if we had an ENOSPC in the
@@ -123,7 +125,7 @@ DECLARE_SPACE_INFO_UPDATE(bytes_pinned, "pinned");
 int btrfs_init_space_info(struct btrfs_fs_info *fs_info);
 void btrfs_update_space_info(struct btrfs_fs_info *info, u64 flags,
 			     u64 total_bytes, u64 bytes_used,
-			     u64 bytes_readonly,
+			     u64 bytes_readonly, u64 bytes_zone_unusable,
 			     struct btrfs_space_info **space_info);
 struct btrfs_space_info *btrfs_find_space_info(struct btrfs_fs_info *info,
 					       u64 flags);

fs/btrfs/sysfs.c

@@ -666,6 +666,7 @@ SPACE_INFO_ATTR(bytes_pinned);
 SPACE_INFO_ATTR(bytes_reserved);
 SPACE_INFO_ATTR(bytes_may_use);
 SPACE_INFO_ATTR(bytes_readonly);
+SPACE_INFO_ATTR(bytes_zone_unusable);
 SPACE_INFO_ATTR(disk_used);
 SPACE_INFO_ATTR(disk_total);
 BTRFS_ATTR(space_info, total_bytes_pinned,
@@ -679,6 +680,7 @@ static struct attribute *space_info_attrs[] = {
 	BTRFS_ATTR_PTR(space_info, bytes_reserved),
 	BTRFS_ATTR_PTR(space_info, bytes_may_use),
 	BTRFS_ATTR_PTR(space_info, bytes_readonly),
+	BTRFS_ATTR_PTR(space_info, bytes_zone_unusable),
 	BTRFS_ATTR_PTR(space_info, disk_used),
 	BTRFS_ATTR_PTR(space_info, disk_total),
 	BTRFS_ATTR_PTR(space_info, total_bytes_pinned),

fs/btrfs/zoned.c

@@ -1160,3 +1160,24 @@ int btrfs_load_block_group_zone_info(struct btrfs_block_group *cache, bool new)
 
 	return ret;
 }
+
+void btrfs_calc_zone_unusable(struct btrfs_block_group *cache)
+{
+	u64 unusable, free;
+
+	if (!btrfs_is_zoned(cache->fs_info))
+		return;
+
+	WARN_ON(cache->bytes_super != 0);
+	unusable = cache->alloc_offset - cache->used;
+	free = cache->length - cache->alloc_offset;
+
+	/* We only need ->free_space in ALLOC_SEQ block groups */
+	cache->last_byte_to_unpin = (u64)-1;
+	cache->cached = BTRFS_CACHE_FINISHED;
+	cache->free_space_ctl->free_space = free;
+	cache->zone_unusable = unusable;
+
+	/* Should not have any excluded extents. Just in case, though */
+	btrfs_free_excluded_extents(cache);
+}

fs/btrfs/zoned.h

@@ -42,6 +42,7 @@ int btrfs_reset_device_zone(struct btrfs_device *device, u64 physical,
 			    u64 length, u64 *bytes);
 int btrfs_ensure_empty_zones(struct btrfs_device *device, u64 start, u64 size);
 int btrfs_load_block_group_zone_info(struct btrfs_block_group *cache, bool new);
+void btrfs_calc_zone_unusable(struct btrfs_block_group *cache);
 #else /* CONFIG_BLK_DEV_ZONED */
 static inline int btrfs_get_dev_zone(struct btrfs_device *device, u64 pos,
 				     struct blk_zone *zone)
@@ -123,6 +124,8 @@ static inline int btrfs_load_block_group_zone_info(
 	return 0;
 }
 
+static inline void btrfs_calc_zone_unusable(struct btrfs_block_group *cache) { }
+
 #endif
 
 static inline bool btrfs_dev_is_sequential(struct btrfs_device *device, u64 pos)