btrfs: track discardable extents for async discard
The number of discardable extents will serve as the rate limiting metric
for how often we should discard. This keeps track of discardable extents
in the free space caches by maintaining deltas and propagating them to
the global count.
The deltas are calculated from 2 values stored in PREV and CURR entries,
then propagated up to the global discard ctl. The current counter value
becomes the previous counter value after update.
Signed-off-by: Dennis Zhou <dennis@kernel.org>
Reviewed-by: David Sterba <dsterba@suse.com>
[ update changelog ]
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 7131704..533c5ea 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -101,6 +101,14 @@ struct btrfs_ref;
#define BTRFS_MAX_EXTENT_SIZE SZ_128M
+/*
+ * Deltas are an effective way to populate global statistics. Give macro names
+ * to make it clear what we're doing. An example is discard_extents in
+ * btrfs_free_space_ctl.
+ */
+#define BTRFS_STAT_NR_ENTRIES 2
+#define BTRFS_STAT_CURR 0
+#define BTRFS_STAT_PREV 1
/*
* Count how many BTRFS_MAX_EXTENT_SIZE cover the @size
@@ -458,6 +466,7 @@ struct btrfs_discard_ctl {
spinlock_t lock;
struct btrfs_block_group *block_group;
struct list_head discard_list[BTRFS_NR_DISCARD_LISTS];
+ atomic_t discardable_extents;
};
/* delayed seq elem */