Cache the value of __d_entry_type in d_is_dir and test if it equal to
DCACHE_DIRECTORY_TYPE or DCACHE_AUTODIR_TYPE.
The generated assembly goes from:
movl (%rdi), %eax # MEM[(volatile __u32 *)dentry_3(D)], tmp73
andl $7340032, %eax #, tmp73
cmpl $2097152, %eax #, tmp73
je .L1091 #,
movl (%rdi), %eax # MEM[(volatile __u32 *)dentry_3(D)], tmp74
andl $7340032, %eax #, tmp74
cmpl $3145728, %eax #, tmp74
je .L1091 #,
to:
movl (%rdi), %eax # MEM[(volatile __u32 *)dentry_3(D)], tmp71
andl $6291456, %eax #, tmp71
cmpl $2097152, %eax #, tmp71
jne .L1091 #,
Which with only one read of d_flags, one comparison and one jump is
dramatically better code.
As __d_entry_type is not written to allow the compiler to optimize
away anything that it does, when it is possible and reasonable to
optimize things away the optimization needs to be performend manually.
Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
---
include/linux/dcache.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 5b69856b45a2..82eb50aaf446 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -443,7 +443,8 @@ static inline bool d_is_autodir(const struct dentry *dentry)
static inline bool d_is_dir(const struct dentry *dentry)
{
- return d_can_lookup(dentry) || d_is_autodir(dentry);
+ unsigned type = __d_entry_type(dentry);
+ return (type == DCACHE_DIRECTORY_TYPE) || (type == DCACHE_AUTODIR_TYPE);
}
static inline bool d_is_symlink(const struct dentry *dentry)
--
2.2.1
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
