Re: dentry cache order 7 is broken

["David S. Miller" <davem@redhat.com>]

Mitchell Blank Jr writes:
 >   1. The inode-cache has the exact same problem, but it'll require a lot
 >      of RAM to run into it.  The buffer and page caches don't have the
 >      same problem.

Yep, fix attached.  You just need 1GB ram to hit that case.

 >   2. Given that D_HASHBITS is not a constant I wonder if there isn't
 >      a more efficient hash to be found.  But I guess I'll leave that
 >      to the hashing experts.

For the moment anything is better than when you hit this
bug :-)

--- fs/inode.c.~1~	Sun Feb  4 20:45:36 2001
+++ fs/inode.c	Thu Feb  8 01:21:07 2001
@@ -729,7 +729,8 @@
 static inline unsigned long hash(struct super_block *sb, unsigned long i_ino)
 {
 	unsigned long tmp = i_ino + ((unsigned long) sb / L1_CACHE_BYTES);
-	tmp = tmp + (tmp >> I_HASHBITS) + (tmp >> I_HASHBITS*2);
+	tmp = tmp + (tmp >> I_HASHBITS) +
+		(tmp >> (I_HASHBITS+(I_HASHBITS/2)));
 	return tmp & I_HASHMASK;
 }
 
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