vfs: use 'unsigned long' accesses for dcache name comparison and hashing

Ok, this is hacky, and only works on little-endian machines with goo
unaligned handling.  And even then only with CONFIG_DEBUG_PAGEALLOC
disabled, since it can access up to 7 bytes after the pathname.

But it runs like a bat out of hell.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 23 insertions, 0 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index bcbdb33fcc2..ffd47a16d87 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -144,6 +144,28 @@ int proc_nr_dentry(ctl_table *table, int write, void __user *buffer,
 static inline int dentry_cmp(const unsigned char *cs, size_t scount,
                                 const unsigned char *ct, size_t tcount)
 {
+#ifdef CONFIG_DCACHE_WORD_ACCESS
+        unsigned long a,b,mask;
+
+        if (unlikely(scount != tcount))
+                return 1;
+
+        for (;;) {
+                a = *(unsigned long *)cs;
+                b = *(unsigned long *)ct;
+                if (tcount < sizeof(unsigned long))
+                        break;
+                if (unlikely(a != b))
+                        return 1;
+                cs += sizeof(unsigned long);
+                ct += sizeof(unsigned long);
+                tcount -= sizeof(unsigned long);
+                if (!tcount)
+                        return 0;
+        }
+        mask = ~(~0ul << tcount*8);
+        return unlikely(!!((a ^ b) & mask));
+#else
         if (scount != tcount)
                 return 1;
 
@@ -155,6 +177,7 @@ static inline int dentry_cmp(const unsigned char *cs, size_t scount,
                 tcount--;
         } while (tcount);
         return 0;
+#endif
 }
 
 static void __d_free(struct rcu_head *head)