From e631df89cd5d638a9d7c152dd9b0a92643efab3e Mon Sep 17 00:00:00 2001 From: Mateusz Guzik Date: Fri, 7 Nov 2025 15:21:47 +0100 Subject: fs: speed up path lookup with cheaper handling of MAY_EXEC The generic inode_permission() routine does work which is known to be of no significance for lookup. There are checks for MAY_WRITE, while the requested permission is MAY_EXEC. Additionally devcgroup_inode_permission() is called to check for devices, but it is an invariant the inode is a directory. Absent a ->permission func, execution lands in generic_permission() which checks upfront if the requested permission is granted for everyone. We can elide the branches which are guaranteed to be false and cut straight to the check if everyone happens to be allowed MAY_EXEC on the inode (which holds true most of the time). Moreover, filesystems which provide their own ->permission routine can take advantage of the optimization by setting the IOP_FASTPERM_MAY_EXEC flag on their inodes, which they can legitimately do if their MAY_EXEC handling matches generic_permission(). As a simple benchmark, as part of compilation gcc issues access(2) on numerous long paths, for example /usr/lib/gcc/x86_64-linux-gnu/12/crtendS.o Issuing access(2) on it in a loop on ext4 on Sapphire Rapids (ops/s): before: 3797556 after: 3987789 (+5%) Note: this depends on the not-yet-landed ext4 patch to mark inodes with cache_no_acl() Signed-off-by: Mateusz Guzik Link: https://patch.msgid.link/20251107142149.989998-2-mjguzik@gmail.com Reviewed-by: Jan Kara Signed-off-by: Christian Brauner --- include/linux/fs.h | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) (limited to 'include/linux') diff --git a/include/linux/fs.h b/include/linux/fs.h index c895146c1444..ff69734b9fde 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -659,13 +659,14 @@ is_uncached_acl(struct posix_acl *acl) return (long)acl & 1; } -#define IOP_FASTPERM 0x0001 -#define IOP_LOOKUP 0x0002 -#define IOP_NOFOLLOW 0x0004 -#define IOP_XATTR 0x0008 +#define IOP_FASTPERM 0x0001 +#define IOP_LOOKUP 0x0002 +#define IOP_NOFOLLOW 0x0004 +#define IOP_XATTR 0x0008 #define IOP_DEFAULT_READLINK 0x0010 -#define IOP_MGTIME 0x0020 -#define IOP_CACHED_LINK 0x0040 +#define IOP_MGTIME 0x0020 +#define IOP_CACHED_LINK 0x0040 +#define IOP_FASTPERM_MAY_EXEC 0x0080 /* * Inode state bits. Protected by inode->i_lock -- cgit v1.2.3