Btrfs: Cache free inode numbers in memory

Currently btrfs stores the highest objectid of the fs tree, and it always
returns (highest+1) inode number when we create a file, so inode numbers
won't be reclaimed when we delete files, so we'll run out of inode numbers
as we keep create/delete files in 32bits machines.

This fixes it, and it works similarly to how we cache free space in block
cgroups.

We start a kernel thread to read the file tree. By scanning inode items,
we know which chunks of inode numbers are free, and we cache them in
an rb-tree.

Because we are searching the commit root, we have to carefully handle the
cross-transaction case.

The rb-tree is a hybrid extent+bitmap tree, so if we have too many small
chunks of inode numbers, we'll use bitmaps. Initially we allow 16K ram
of extents, and a bitmap will be used if we exceed this threshold. The
extents threshold is adjusted in runtime.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>

1 files changed, 9 insertions, 6 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index d17e4a3b8bf7..c96a4e4c5566 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1102,6 +1102,15 @@ struct btrfs_root {
         spinlock_t accounting_lock;
         struct btrfs_block_rsv *block_rsv;
 
+        /* free ino cache stuff */
+        struct mutex fs_commit_mutex;
+        struct btrfs_free_space_ctl *free_ino_ctl;
+        enum btrfs_caching_type cached;
+        spinlock_t cache_lock;
+        wait_queue_head_t cache_wait;
+        struct btrfs_free_space_ctl *free_ino_pinned;
+        u64 cache_progress;
+
         struct mutex log_mutex;
         wait_queue_head_t log_writer_wait;
         wait_queue_head_t log_commit_wait[2];
@@ -2408,12 +2417,6 @@ int btrfs_del_orphan_item(struct btrfs_trans_handle *trans,
                           struct btrfs_root *root, u64 offset);
 int btrfs_find_orphan_item(struct btrfs_root *root, u64 offset);
 
-/* inode-map.c */
-int btrfs_find_free_objectid(struct btrfs_trans_handle *trans,
-                             struct btrfs_root *fs_root,
-                             u64 dirid, u64 *objectid);
-int btrfs_find_highest_inode(struct btrfs_root *fs_root, u64 *objectid);
-
 /* inode-item.c */
 int btrfs_insert_inode_ref(struct btrfs_trans_handle *trans,
                            struct btrfs_root *root,