[PATCH v3 2/3] btrfs: utilize IOP_FASTPERM_MAY_EXEC

[Mateusz Guzik <mjguzik@gmail.com>]

Root filesystem was ext4, btrfs was mounted on /testfs.

Then issuing access(2) in a loop on /testfs/repos/linux/include/linux/fs.h
on Sapphire Rapids (ops/s):

before: 3447976
after:	3620879 (+5%)

Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
---
 fs/btrfs/inode.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 42da39c1e5b5..1a560f7298bf 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -5852,6 +5852,8 @@ struct btrfs_inode *btrfs_iget(u64 ino, struct btrfs_root *root)
 	if (ret)
 		return ERR_PTR(ret);
 
+	if (S_ISDIR(inode->vfs_inode.i_mode))
+		inode->vfs_inode.i_opflags |= IOP_FASTPERM_MAY_EXEC;
 	unlock_new_inode(&inode->vfs_inode);
 	return inode;
 }
@@ -6803,8 +6805,11 @@ static int btrfs_create_common(struct inode *dir, struct dentry *dentry,
 	}
 
 	ret = btrfs_create_new_inode(trans, &new_inode_args);
-	if (!ret)
+	if (!ret) {
+		if (S_ISDIR(inode->i_mode))
+			inode->i_opflags |= IOP_FASTPERM_MAY_EXEC;
 		d_instantiate_new(dentry, inode);
+	}
 
 	btrfs_end_transaction(trans);
 	btrfs_btree_balance_dirty(fs_info);
@@ -9163,6 +9168,11 @@ int btrfs_prealloc_file_range_trans(struct inode *inode,
 					   min_size, actual_len, alloc_hint, trans);
 }
 
+/*
+ * NOTE: in case you are adding MAY_EXEC check for directories:
+ * we are marking them with IOP_FASTPERM_MAY_EXEC, allowing path lookup to
+ * elide calls here.
+ */
 static int btrfs_permission(struct mnt_idmap *idmap,
 			    struct inode *inode, int mask)
 {
-- 
2.48.1