Track negative entries v3

Track negative dentries by recording the generation number of the parent
directory in d_fsdata. The generation number for the parent directory is
recorded in the inode_info, which increments every time the lock on the
directory is dropped.

If the generation number of the parent directory and the negative dentry
matches, there is no need to perform the revalidate, else a revalidate
is forced. This improves performance in situations where nodes look for
the same non-existent file multiple times.

Thanks Mark for explaining the DLM sequence.

Signed-off-by: Goldwyn Rodrigues <[e-mail]>
Signed-off-by: Joel Becker <[e-mail]>

fs/ocfs2/dcache.c

···
 #include "inode.h"
 #include "super.h"
 
+void ocfs2_dentry_attach_gen(struct dentry *dentry)
+{
+	unsigned long gen =
+		OCFS2_I(dentry->d_parent->d_inode)->ip_dir_lock_gen;
+	BUG_ON(dentry->d_inode);
+	dentry->d_fsdata = (void *)gen;
+}
+
 
 static int ocfs2_dentry_revalidate(struct dentry *dentry,
 				   struct nameidata *nd)
···
 	mlog_entry("(0x%p, '%.*s')\n", dentry,
 		   dentry->d_name.len, dentry->d_name.name);
 
-	/* Never trust a negative dentry - force a new lookup. */
+	/* For a negative dentry -
+	 * check the generation number of the parent and compare with the
+	 * one stored in the inode.
+	 */
 	if (inode == NULL) {
-		mlog(0, "negative dentry: %.*s\n", dentry->d_name.len,
-		     dentry->d_name.name);
-		goto bail;
+		unsigned long gen = (unsigned long) dentry->d_fsdata;
+		unsigned long pgen =
+			OCFS2_I(dentry->d_parent->d_inode)->ip_dir_lock_gen;
+		mlog(0, "negative dentry: %.*s parent gen: %lu "
+			"dentry gen: %lu\n",
+			dentry->d_name.len, dentry->d_name.name, pgen, gen);
+		if (gen != pgen)
+			goto bail;
+		goto valid;
 	}
 
 	BUG_ON(!osb);
···
 		goto bail;
 	}
 
+valid:
 	ret = 1;
 
 bail:
···
 	 */
 	if (!inode)
 		return 0;
+
+	if (!dentry->d_inode && dentry->d_fsdata) {
+		/* Converting a negative dentry to positive
+		   Clear dentry->d_fsdata */
+		dentry->d_fsdata = dl = NULL;
+	}
 
 	if (dl) {
 		mlog_bug_on_msg(dl->dl_parent_blkno != parent_blkno,
···
 
 out:
 	iput(inode);
+	ocfs2_dentry_attach_gen(dentry);
 }
 
 /*

fs/ocfs2/dcache.h

···
 		       struct inode *old_dir, struct inode *new_dir);
 
 extern spinlock_t dentry_attach_lock;
+void ocfs2_dentry_attach_gen(struct dentry *dentry);
 
 #endif /* OCFS2_DCACHE_H */

fs/ocfs2/dlmglue.c

···
 {
 	struct inode *inode;
 	struct address_space *mapping;
+	struct ocfs2_inode_info *oi;
 
        	inode = ocfs2_lock_res_inode(lockres);
 	mapping = inode->i_mapping;
+
+	if (S_ISDIR(inode->i_mode)) {
+		oi = OCFS2_I(inode);
+		oi->ip_dir_lock_gen++;
+		mlog(0, "generation: %u\n", oi->ip_dir_lock_gen);
+		goto out;
+	}
 
 	if (!S_ISREG(inode->i_mode))
 		goto out;

fs/ocfs2/inode.c

···
 		    else
 			    inode->i_fop = &ocfs2_dops_no_plocks;
 		    i_size_write(inode, le64_to_cpu(fe->i_size));
+		    OCFS2_I(inode)->ip_dir_lock_gen = 1;
 		    break;
 	    case S_IFLNK:
 		    if (ocfs2_inode_is_fast_symlink(inode))

fs/ocfs2/inode.h

···
 	/* Only valid if the inode is the dir. */
 	u32				ip_last_used_slot;
 	u64				ip_last_used_group;
+	u32				ip_dir_lock_gen;
 
 	struct ocfs2_alloc_reservation	ip_la_data_resv;
 };

fs/ocfs2/namei.c

···
 			ret = ERR_PTR(status);
 			goto bail_unlock;
 		}
-	}
+	} else
+		ocfs2_dentry_attach_gen(dentry);
 
 bail_unlock:
 	/* Don't drop the cluster lock until *after* the d_add --