[PATCH 2/2] btrfs: add size class stats to sysfs

[Boris Burkov <boris@bur.io>]

Make it possible to see the distribution of size classes for block
groups. Helpful for testing and debugging the allocator w.r.t. to size
classes.

Signed-off-by: Boris Burkov <boris@bur.io>
---
 fs/btrfs/sysfs.c | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index 108aa3876186..e1ae4d2323d6 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -9,6 +9,7 @@
 #include <linux/spinlock.h>
 #include <linux/completion.h>
 #include <linux/bug.h>
+#include <linux/list.h>
 #include <crypto/hash.h>
 #include "messages.h"
 #include "ctree.h"
@@ -778,6 +779,42 @@ static ssize_t btrfs_chunk_size_store(struct kobject *kobj,
 	return len;
 }
 
+static ssize_t btrfs_size_classes_show(struct kobject *kobj,
+				       struct kobj_attribute *a, char *buf)
+{
+	struct btrfs_space_info *sinfo = to_space_info(kobj);
+	struct btrfs_block_group *bg;
+	int none = 0;
+	int small = 0;
+	int medium = 0;
+	int large = 0;
+	int i;
+
+	down_read(&sinfo->groups_sem);
+	for (i = 0; i < BTRFS_NR_RAID_TYPES; ++i) {
+		list_for_each_entry(bg, &sinfo->block_groups[i], list) {
+			if (!btrfs_block_group_should_use_size_class(bg))
+				continue;
+			switch (bg->size_class) {
+			case BTRFS_BG_SZ_NONE:
+				none++;
+				break;
+			case BTRFS_BG_SZ_SMALL:
+				small++;
+				break;
+			case BTRFS_BG_SZ_MEDIUM:
+				medium++;
+				break;
+			case BTRFS_BG_SZ_LARGE:
+				large++;
+				break;
+			}
+		}
+	}
+	up_read(&sinfo->groups_sem);
+	return sysfs_emit(buf, "%d %d %d %d\n", none, small, medium, large);
+}
+
 #ifdef CONFIG_BTRFS_DEBUG
 /*
  * Request chunk allocation with current chunk size.
@@ -835,6 +872,7 @@ SPACE_INFO_ATTR(bytes_zone_unusable);
 SPACE_INFO_ATTR(disk_used);
 SPACE_INFO_ATTR(disk_total);
 BTRFS_ATTR_RW(space_info, chunk_size, btrfs_chunk_size_show, btrfs_chunk_size_store);
+BTRFS_ATTR(space_info, size_classes, btrfs_size_classes_show);
 
 static ssize_t btrfs_sinfo_bg_reclaim_threshold_show(struct kobject *kobj,
 						     struct kobj_attribute *a,
@@ -887,6 +925,7 @@ static struct attribute *space_info_attrs[] = {
 	BTRFS_ATTR_PTR(space_info, disk_total),
 	BTRFS_ATTR_PTR(space_info, bg_reclaim_threshold),
 	BTRFS_ATTR_PTR(space_info, chunk_size),
+	BTRFS_ATTR_PTR(space_info, size_classes),
 #ifdef CONFIG_BTRFS_DEBUG
 	BTRFS_ATTR_PTR(space_info, force_chunk_alloc),
 #endif
-- 
2.38.1