[RFC PATCH] add lookup hint for network file systems

[ASANO Masahiro <masano@tnes.nec.co.jp>]

Hi,

I'm trying to speeding up mkdir(2) for network file systems.
A typical mkdir(2) calls two inode_operations: lookup and mkdir.
The lookup operation would fail with ENOENT in common case.  I think
it is unnecessary because the subsequent mkdir operation can check it.
In case of creat(2), lookup operation is called with the LOOKUP_CREATE
flag, so individual filesystem can omit real lookup. e.g. nfs_lookup().

Here is a sample patch which uses LOOKUP_CREATE and O_EXCL on mkdir,
symlink and mknod.  This uses the gadget for creat(2).

And here is the result of a benchmark on NFSv3.
  mkdir(2) 10,000 times:
    original  50.5 sec
    patched   29.0 sec

Signed-off-by: ASANO Masahiro <masano@tnes.nec.co.jp>

---

 fs/namei.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

5273ee304b4dc1096432dc3f3aa9183e20afab1d
diff --git a/fs/namei.c b/fs/namei.c
index 184fe4a..209867d 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1759,6 +1759,8 @@ struct dentry *lookup_create(struct name
 	if (nd->last_type != LAST_NORM)
 		goto fail;
 	nd->flags &= ~LOOKUP_PARENT;
+	nd->flags |= LOOKUP_CREATE;
+	nd->intent.open.flags = O_EXCL;
 
 	/*
 	 * Do the final lookup.
-- 
1.3.3

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