btrfs: embed delayed root to struct btrfs_fs_info

The fs_info::delayed_root is allocated dynamically but there's only one
instance per filesystem so we can embed it into the fs_info itself.
The two object have the same lifetime and delayed roots are always
present so we don't need to allocate it on demand from slab.

There's still some space left in fs_info until the 4K so there won't be
an spill over to next page on release config (size grows from 3880 to
3952). In case we want to shrink fs_info there are still holes to fill
or we can separate other non-core or optional structures if needed.

Link: https://lore.kernel.org/all/cover.1767979013.git.dsterba@suse.com/
Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: David Sterba <dsterba@suse.com>

4 files changed, 30 insertions, 35 deletions

diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
index 2286bee2c6d3..a752646257df 100644
--- a/fs/btrfs/delayed-inode.c
+++ b/fs/btrfs/delayed-inode.c
@@ -257,7 +257,7 @@ static struct btrfs_delayed_node *btrfs_next_delayed_node(
 	struct list_head *p;
 	struct btrfs_delayed_node *next = NULL;
 
-	delayed_root = node->root->fs_info->delayed_root;
+	delayed_root = &node->root->fs_info->delayed_root;
 	spin_lock(&delayed_root->lock);
 	if (!test_bit(BTRFS_DELAYED_NODE_IN_LIST, &node->flags)) {
 		/* not in the list */
@@ -287,7 +287,7 @@ static void __btrfs_release_delayed_node(
 	if (!delayed_node)
 		return;
 
-	delayed_root = delayed_node->root->fs_info->delayed_root;
+	delayed_root = &delayed_node->root->fs_info->delayed_root;
 
 	mutex_lock(&delayed_node->mutex);
 	if (delayed_node->count)
@@ -425,7 +425,7 @@ static int __btrfs_add_delayed_item(struct btrfs_delayed_node *delayed_node,
 		delayed_node->index_cnt = ins->index + 1;
 
 	delayed_node->count++;
-	atomic_inc(&delayed_node->root->fs_info->delayed_root->items);
+	atomic_inc(&delayed_node->root->fs_info->delayed_root.items);
 	return 0;
 }
 
@@ -452,7 +452,7 @@ static void __btrfs_remove_delayed_item(struct btrfs_delayed_item *delayed_item)
 	/* If it's in a rbtree, then we need to have delayed node locked. */
 	lockdep_assert_held(&delayed_node->mutex);
 
-	delayed_root = delayed_node->root->fs_info->delayed_root;
+	delayed_root = &delayed_node->root->fs_info->delayed_root;
 
 	if (delayed_item->type == BTRFS_DELAYED_INSERTION_ITEM)
 		root = &delayed_node->ins_root;
@@ -988,7 +988,7 @@ static void btrfs_release_delayed_inode(struct btrfs_delayed_node *delayed_node)
 		clear_bit(BTRFS_DELAYED_NODE_INODE_DIRTY, &delayed_node->flags);
 		delayed_node->count--;
 
-		delayed_root = delayed_node->root->fs_info->delayed_root;
+		delayed_root = &delayed_node->root->fs_info->delayed_root;
 		finish_one_item(delayed_root);
 	}
 }
@@ -1002,7 +1002,7 @@ static void btrfs_release_delayed_iref(struct btrfs_delayed_node *delayed_node)
 		ASSERT(delayed_node->root);
 		delayed_node->count--;
 
-		delayed_root = delayed_node->root->fs_info->delayed_root;
+		delayed_root = &delayed_node->root->fs_info->delayed_root;
 		finish_one_item(delayed_root);
 	}
 }
@@ -1168,7 +1168,7 @@ static int __btrfs_run_delayed_items(struct btrfs_trans_handle *trans, int nr)
 	block_rsv = trans->block_rsv;
 	trans->block_rsv = &fs_info->delayed_block_rsv;
 
-	delayed_root = fs_info->delayed_root;
+	delayed_root = &fs_info->delayed_root;
 
 	curr_node = btrfs_first_delayed_node(delayed_root, &curr_delayed_node_tracker);
 	while (curr_node && (!count || nr--)) {
@@ -1417,7 +1417,7 @@ void btrfs_assert_delayed_root_empty(struct btrfs_fs_info *fs_info)
 	struct btrfs_ref_tracker delayed_node_tracker;
 	struct btrfs_delayed_node *node;
 
-	node = btrfs_first_delayed_node( fs_info->delayed_root, &delayed_node_tracker);
+	node = btrfs_first_delayed_node(&fs_info->delayed_root, &delayed_node_tracker);
 	if (WARN_ON(node)) {
 		btrfs_delayed_node_ref_tracker_free(node,
 						    &delayed_node_tracker);
@@ -1440,7 +1440,7 @@ static bool could_end_wait(struct btrfs_delayed_root *delayed_root, int seq)
 
 void btrfs_balance_delayed_items(struct btrfs_fs_info *fs_info)
 {
-	struct btrfs_delayed_root *delayed_root = fs_info->delayed_root;
+	struct btrfs_delayed_root *delayed_root = &fs_info->delayed_root;
 
 	if ((atomic_read(&delayed_root->items) < BTRFS_DELAYED_BACKGROUND) ||
 		btrfs_workqueue_normal_congested(fs_info->delayed_workers))
@@ -1970,7 +1970,7 @@ int btrfs_delayed_update_inode(struct btrfs_trans_handle *trans,
 	fill_stack_inode_item(trans, &delayed_node->inode_item, inode);
 	set_bit(BTRFS_DELAYED_NODE_INODE_DIRTY, &delayed_node->flags);
 	delayed_node->count++;
-	atomic_inc(&root->fs_info->delayed_root->items);
+	atomic_inc(&root->fs_info->delayed_root.items);
 release_node:
 	mutex_unlock(&delayed_node->mutex);
 	btrfs_release_delayed_node(delayed_node, &delayed_node_tracker);
@@ -2012,7 +2012,7 @@ int btrfs_delayed_delete_inode_ref(struct btrfs_inode *inode)
 	mutex_lock(&delayed_node->mutex);
 	if (!test_and_set_bit(BTRFS_DELAYED_NODE_DEL_IREF, &delayed_node->flags)) {
 		delayed_node->count++;
-		atomic_inc(&fs_info->delayed_root->items);
+		atomic_inc(&fs_info->delayed_root.items);
 	}
 	mutex_unlock(&delayed_node->mutex);
 	btrfs_release_delayed_node(delayed_node, &delayed_node_tracker);
@@ -2118,7 +2118,7 @@ void btrfs_destroy_delayed_inodes(struct btrfs_fs_info *fs_info)
 	struct btrfs_delayed_node *curr_node, *prev_node;
 	struct btrfs_ref_tracker curr_delayed_node_tracker, prev_delayed_node_tracker;
 
-	curr_node = btrfs_first_delayed_node(fs_info->delayed_root,
+	curr_node = btrfs_first_delayed_node(&fs_info->delayed_root,
 					     &curr_delayed_node_tracker);
 	while (curr_node) {
 		__btrfs_kill_delayed_node(curr_node);
diff --git a/fs/btrfs/delayed-inode.h b/fs/btrfs/delayed-inode.h
index b09d4ec8c77d..fc752863f89b 100644
--- a/fs/btrfs/delayed-inode.h
+++ b/fs/btrfs/delayed-inode.h
@@ -30,21 +30,6 @@ enum btrfs_delayed_item_type {
 	BTRFS_DELAYED_DELETION_ITEM
 };
 
-struct btrfs_delayed_root {
-	spinlock_t lock;
-	struct list_head node_list;
-	/*
-	 * Used for delayed nodes which is waiting to be dealt with by the
-	 * worker. If the delayed node is inserted into the work queue, we
-	 * drop it from this list.
-	 */
-	struct list_head prepare_list;
-	atomic_t items;		/* for delayed items */
-	atomic_t items_seq;	/* for delayed items */
-	int nodes;		/* for delayed nodes */
-	wait_queue_head_t wait;
-};
-
 struct btrfs_ref_tracker_dir {
 #ifdef CONFIG_BTRFS_DEBUG
 	struct ref_tracker_dir dir;
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 32fffb0557e5..665440ecce12 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -22,6 +22,7 @@
 #include "disk-io.h"
 #include "transaction.h"
 #include "btrfs_inode.h"
+#include "delayed-inode.h"
 #include "bio.h"
 #include "print-tree.h"
 #include "locking.h"
@@ -1217,7 +1218,6 @@ void btrfs_free_fs_info(struct btrfs_fs_info *fs_info)
 	btrfs_free_stripe_hash_table(fs_info);
 	btrfs_free_ref_cache(fs_info);
 	kfree(fs_info->balance_ctl);
-	kfree(fs_info->delayed_root);
 	free_global_roots(fs_info);
 	btrfs_put_root(fs_info->tree_root);
 	btrfs_put_root(fs_info->chunk_root);
@@ -2942,11 +2942,7 @@ static int init_mount_fs_info(struct btrfs_fs_info *fs_info, struct super_block
 	if (ret)
 		return ret;
 
-	fs_info->delayed_root = kmalloc(sizeof(struct btrfs_delayed_root),
-					GFP_KERNEL);
-	if (!fs_info->delayed_root)
-		return -ENOMEM;
-	btrfs_init_delayed_root(fs_info->delayed_root);
+	btrfs_init_delayed_root(&fs_info->delayed_root);
 
 	if (sb_rdonly(sb))
 		set_bit(BTRFS_FS_STATE_RO, &fs_info->fs_state);
diff --git a/fs/btrfs/fs.h b/fs/btrfs/fs.h
index 5bbc993a66e1..d315530a2928 100644
--- a/fs/btrfs/fs.h
+++ b/fs/btrfs/fs.h
@@ -44,7 +44,6 @@ struct btrfs_block_group;
 struct btrfs_root;
 struct btrfs_fs_devices;
 struct btrfs_transaction;
-struct btrfs_delayed_root;
 struct btrfs_balance_control;
 struct btrfs_subpage_info;
 struct btrfs_stripe_hash_table;
@@ -464,6 +463,21 @@ struct btrfs_commit_stats {
 	u64 critical_section_start_time;
 };
 
+struct btrfs_delayed_root {
+	spinlock_t lock;
+	struct list_head node_list;
+	/*
+	 * Used for delayed nodes which is waiting to be dealt with by the
+	 * worker. If the delayed node is inserted into the work queue, we
+	 * drop it from this list.
+	 */
+	struct list_head prepare_list;
+	atomic_t items;		/* for delayed items */
+	atomic_t items_seq;	/* for delayed items */
+	int nodes;		/* for delayed nodes */
+	wait_queue_head_t wait;
+};
+
 struct btrfs_fs_info {
 	u8 chunk_tree_uuid[BTRFS_UUID_SIZE];
 	unsigned long flags;
@@ -817,7 +831,7 @@ struct btrfs_fs_info {
 	/* Filesystem state */
 	unsigned long fs_state;
 
-	struct btrfs_delayed_root *delayed_root;
+	struct btrfs_delayed_root delayed_root;
 
 	/* Entries are eb->start >> nodesize_bits */
 	struct xarray buffer_tree;