[Ocfs2-devel] [PATCH] Track negative dentries

[Goldwyn Rodrigues <rgoldwyn@gmail.com>]

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 <rgoldwyn@suse.de>
---
diff --git a/fs/ocfs2/dcache.c b/fs/ocfs2/dcache.c
index b4957c7..f29095b 100644
--- a/fs/ocfs2/dcache.c
+++ b/fs/ocfs2/dcache.c
@@ -40,6 +40,16 @@
 #include "inode.h"
 #include "super.h"

+void ocfs2_dentry_attach_gen(struct dentry *dentry)
+{
+	int *gen = (int *)kmalloc(sizeof(int), GFP_KERNEL);
+	*gen = OCFS2_I(dentry->d_parent->d_inode)->ip_generation;
+	/* Generation numbers are specifically for negative dentries */
+	if (dentry->d_inode)
+		BUG();
+	dentry->d_fsdata = (void *)gen;
+}
+

 static int ocfs2_dentry_revalidate(struct dentry *dentry,
 				   struct nameidata *nd)
@@ -51,10 +61,21 @@ static int ocfs2_dentry_revalidate(struct dentry *dentry,
 	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);
+		int *gen = (int *)dentry->d_fsdata;
+		int parent_gen =
+			OCFS2_I(dentry->d_parent->d_inode)->ip_generation;
+		mlog(0, "negative dentry: %.*s parent gen: %u dentry gen: %u\n",
+				dentry->d_name.len, dentry->d_name.name,
+				parent_gen, *gen);
+		if (*gen == parent_gen)
+			ret = 1;
+		else
+			*gen = parent_gen;
 		goto bail;
 	}

@@ -227,6 +248,13 @@ int ocfs2_dentry_attach_lock(struct dentry *dentry,
 	if (!inode)
 		return 0;

+	if (!dentry->d_inode && dentry->d_fsdata) {
+		/* Converting a negative dentry to positive
+		   Clear dentry->d_fsdata */
+		kfree(dentry->d_fsdata);
+		dentry->d_fsdata = dl = NULL;
+	}
+
 	if (dl) {
 		mlog_bug_on_msg(dl->dl_parent_blkno != parent_blkno,
 				" \"%.*s\": old parent: %llu, new: %llu\n",
@@ -451,6 +479,8 @@ static void ocfs2_dentry_iput(struct dentry
*dentry, struct inode *inode)
 	ocfs2_dentry_lock_put(OCFS2_SB(dentry->d_sb), dl);

 out:
+	/* Attach generation number to dentry */
+	ocfs2_dentry_attach_gen(dentry);
 	iput(inode);
 }

@@ -500,7 +530,15 @@ out_move:
 	d_move(dentry, target);
 }

+static void ocfs2_dentry_release(struct dentry *dentry)
+{
+	/* Free the generation number stored in negative dentry */
+	if (!dentry->d_inode && dentry->d_fsdata)
+		kfree(dentry->d_fsdata);
+}
+
 const struct dentry_operations ocfs2_dentry_ops = {
 	.d_revalidate		= ocfs2_dentry_revalidate,
 	.d_iput			= ocfs2_dentry_iput,
+	.d_release		= ocfs2_dentry_release,
 };
diff --git a/fs/ocfs2/dcache.h b/fs/ocfs2/dcache.h
index f5dd178..b79eff7 100644
--- a/fs/ocfs2/dcache.h
+++ b/fs/ocfs2/dcache.h
@@ -64,5 +64,6 @@ void ocfs2_dentry_move(struct dentry *dentry, struct
dentry *target,
 		       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 */
diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
index 39eb16a..d5fb79b 100644
--- a/fs/ocfs2/dlmglue.c
+++ b/fs/ocfs2/dlmglue.c
@@ -2565,7 +2565,6 @@ void ocfs2_inode_unlock(struct inode *inode,
 	if (!ocfs2_is_hard_readonly(OCFS2_SB(inode->i_sb)) &&
 	    !ocfs2_mount_local(osb))
 		ocfs2_cluster_unlock(OCFS2_SB(inode->i_sb), lockres, level);
-
 	mlog_exit_void();
 }

@@ -3635,10 +3634,18 @@ static int ocfs2_data_convert_worker(struct
ocfs2_lock_res *lockres,
 {
 	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_generation++;
+		mlog(0, "generation: %u\n", oi->ip_generation);
+		goto out;
+	}
+
 	if (!S_ISREG(inode->i_mode))
 		goto out;

diff --git a/fs/ocfs2/inode.h b/fs/ocfs2/inode.h
index 9f5f5fc..529729c 100644
--- a/fs/ocfs2/inode.h
+++ b/fs/ocfs2/inode.h
@@ -70,6 +70,8 @@ struct ocfs2_inode_info
 	/* Only valid if the inode is the dir. */
 	u32				ip_last_used_slot;
 	u64				ip_last_used_group;
+	/* Generation number for negative inodes */
+	u32				ip_generation;

 	struct ocfs2_alloc_reservation	ip_la_data_resv;
 };
diff --git a/fs/ocfs2/namei.c b/fs/ocfs2/namei.c
index f171b51..c06753a 100644
--- a/fs/ocfs2/namei.c
+++ b/fs/ocfs2/namei.c
@@ -172,6 +172,8 @@ bail_add:
 			goto bail_unlock;
 		}
 	}
+	else /* Attach generation number for negative dentry */
+		ocfs2_dentry_attach_gen(dentry);

 bail_unlock:
 	/* Don't drop the cluster lock until *after* the d_add --

-- 
Goldwyn