btrfs: utilize IOP_FASTPERM_MAY_EXEC

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>
Link: https://patch.msgid.link/20251107142149.989998-3-mjguzik@gmail.com
Acked-by: David Sterba <dsterba@suse.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 3b1b3a0553eea06229255ad0284d76074bdb958a..36c451a9a0bfa322bcf40e517068e87d3f383d05 100644 (file)
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -5837,6 +5837,8 @@ 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;
 }
@@ -6788,8 +6790,11 @@ 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);
@@ -9169,6 +9174,11 @@ 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)
 {