btrfs: keep track of which extents have been discarded

Async discard will use the free space cache as backing knowledge for
which extents to discard. This patch plumbs knowledge about which
extents need to be discarded into the free space cache from
unpin_extent_range().

An untrimmed extent can merge with everything as this is a new region.
Absorbing trimmed extents is a tradeoff to for greater coalescing which
makes life better for find_free_extent(). Additionally, it seems the
size of a trim isn't as problematic as the trim io itself.

When reading in the free space cache from disk, if sync is set, mark all
extents as trimmed. The current code ensures at transaction commit that
all free space is trimmed when sync is set, so this reflects that.

Signed-off-by: Dennis Zhou <dennis@kernel.org>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 16 insertions, 1 deletions

diff --git a/fs/btrfs/free-space-cache.h b/fs/btrfs/free-space-cache.h
index ba9a23241101..66c073f854dc 100644
--- a/fs/btrfs/free-space-cache.h
+++ b/fs/btrfs/free-space-cache.h
@@ -6,6 +6,14 @@
 #ifndef BTRFS_FREE_SPACE_CACHE_H
 #define BTRFS_FREE_SPACE_CACHE_H
 
+/*
+ * This is the trim state of an extent or bitmap.
+ */
+enum btrfs_trim_state {
+	BTRFS_TRIM_STATE_UNTRIMMED,
+	BTRFS_TRIM_STATE_TRIMMED,
+};
+
 struct btrfs_free_space {
 	struct rb_node offset_index;
 	u64 offset;
@@ -13,8 +21,14 @@ struct btrfs_free_space {
 	u64 max_extent_size;
 	unsigned long *bitmap;
 	struct list_head list;
+	enum btrfs_trim_state trim_state;
 };
 
+static inline bool btrfs_free_space_trimmed(struct btrfs_free_space *info)
+{
+	return (info->trim_state == BTRFS_TRIM_STATE_TRIMMED);
+}
+
 struct btrfs_free_space_ctl {
 	spinlock_t tree_lock;
 	struct rb_root free_space_offset;
@@ -83,7 +97,8 @@ int btrfs_write_out_ino_cache(struct btrfs_root *root,
 void btrfs_init_free_space_ctl(struct btrfs_block_group *block_group);
 int __btrfs_add_free_space(struct btrfs_fs_info *fs_info,
 			   struct btrfs_free_space_ctl *ctl,
-			   u64 bytenr, u64 size);
+			   u64 bytenr, u64 size,
+			   enum btrfs_trim_state trim_state);
 int btrfs_add_free_space(struct btrfs_block_group *block_group,
 			 u64 bytenr, u64 size);
 int btrfs_remove_free_space(struct btrfs_block_group *block_group,