[Ocfs2-devel] [PATCH] Track negative dentries v2

[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..6db61a3 100644
--- a/fs/ocfs2/dcache.c
+++ b/fs/ocfs2/dcache.c
@@ -40,6 +40,16 @@
 #include "inode.h"
 #include "super.h"

+/* Attach a generation number to a negative dentry */
+void ocfs2_dentry_attach_gen(struct dentry *dentry)
+{
+	unsigned long gen = OCFS2_I(dentry->d_parent->d_inode)->ip_generation;
+	/* 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)
@@ -51,11 +61,22 @@ 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);
-		goto bail;
+		unsigned long gen = (unsigned long) dentry->d_fsdata;
+		unsigned long pgen =
+			OCFS2_I(dentry->d_parent->d_inode)->ip_generation;
+		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) {
+			dentry->d_fsdata = (void *) pgen;
+			goto bail;
+		}
+		goto valid;
 	}

 	BUG_ON(!osb);
@@ -96,6 +117,7 @@ static int ocfs2_dentry_revalidate(struct dentry *dentry,
 		goto bail;
 	}

+valid:
 	ret = 1;

 bail:
@@ -227,6 +249,12 @@ 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 */
+		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 +479,7 @@ static void ocfs2_dentry_iput(struct dentry
*dentry, struct inode *inode)
 	ocfs2_dentry_lock_put(OCFS2_SB(dentry->d_sb), dl);

 out:
+	ocfs2_dentry_attach_gen(dentry);
 	iput(inode);
 }

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..bf79dcf 100644
--- a/fs/ocfs2/dlmglue.c
+++ b/fs/ocfs2/dlmglue.c
@@ -3635,10 +3635,18 @@ 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..34bad2c 100644
--- a/fs/ocfs2/inode.h
+++ b/fs/ocfs2/inode.h
@@ -70,6 +70,7 @@ struct ocfs2_inode_info
 	/* Only valid if the inode is the dir. */
 	u32				ip_last_used_slot;
 	u64				ip_last_used_group;
+	u32				ip_generation; /*for -ve dentry */

 	struct ocfs2_alloc_reservation	ip_la_data_resv;
 };
diff --git a/fs/ocfs2/namei.c b/fs/ocfs2/namei.c
index f171b51..e89bce7 100644
--- a/fs/ocfs2/namei.c
+++ b/fs/ocfs2/namei.c
@@ -171,7 +171,8 @@ bail_add:
 			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 --

-- 
Goldwyn