btrfs: zoned: avoid chunk allocation if active block group has enough space

The current extent allocator tries to allocate a new block group when the
existing block groups do not have enough space. On a ZNS device, a new
block group means a new active zone. If the number of active zones has
already reached the max_active_zones, activating a new zone needs to finish
an existing zone, leading to wasting the free space there.

So, instead, it should reuse the existing active block groups as much as
possible when we can't activate any other zones without sacrificing an
already activated block group.

While at it, I converted find_free_extent_update_loop() to check the
found_extent() case early and made the other conditions simpler.

Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 21 insertions, 7 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 53697d942875..9aa429a9a235 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3478,6 +3478,7 @@ struct find_free_extent_ctl {
 	/* Basic allocation info */
 	u64 ram_bytes;
 	u64 num_bytes;
+	u64 min_alloc_size;
 	u64 empty_size;
 	u64 flags;
 	int delalloc;
@@ -3946,18 +3947,30 @@ static int find_free_extent_update_loop(struct btrfs_fs_info *fs_info,
 	    ffe_ctl->have_caching_bg && !ffe_ctl->orig_have_caching_bg)
 		ffe_ctl->orig_have_caching_bg = true;
 
-	if (!ins->objectid && ffe_ctl->loop >= LOOP_CACHING_WAIT &&
-	    ffe_ctl->have_caching_bg)
-		return 1;
-
-	if (!ins->objectid && ++(ffe_ctl->index) < BTRFS_NR_RAID_TYPES)
-		return 1;
-
 	if (ins->objectid) {
 		found_extent(ffe_ctl, ins);
 		return 0;
 	}
 
+	if (ffe_ctl->max_extent_size >= ffe_ctl->min_alloc_size &&
+	    !btrfs_can_activate_zone(fs_info->fs_devices, ffe_ctl->index)) {
+		/*
+		 * If we have enough free space left in an already active block
+		 * group and we can't activate any other zone now, retry the
+		 * active ones with a smaller allocation size.  Returning early
+		 * from here will tell btrfs_reserve_extent() to haven the
+		 * size.
+		 */
+		return -ENOSPC;
+	}
+
+	if (ffe_ctl->loop >= LOOP_CACHING_WAIT && ffe_ctl->have_caching_bg)
+		return 1;
+
+	ffe_ctl->index++;
+	if (ffe_ctl->index < BTRFS_NR_RAID_TYPES)
+		return 1;
+
 	/*
 	 * LOOP_CACHING_NOWAIT, search partially cached block groups, kicking
 	 *			caching kthreads as we move along
@@ -4432,6 +4445,7 @@ again:
 
 	ffe_ctl.ram_bytes = ram_bytes;
 	ffe_ctl.num_bytes = num_bytes;
+	ffe_ctl.min_alloc_size = min_alloc_size;
 	ffe_ctl.empty_size = empty_size;
 	ffe_ctl.flags = flags;
 	ffe_ctl.delalloc = delalloc;