fs: introduce mnt_clone_write
This patch speeds up lmbench lat_mmap test by about another 2% after the
first patch.
Before:
avg = 462.286
std = 5.46106
After:
avg = 453.12
std = 9.58257
(50 runs of each, stddev gives a reasonable confidence)
It does this by introducing mnt_clone_write, which avoids some heavyweight
operations of mnt_want_write if called on a vfsmount which we know already
has a write count; and mnt_want_write_file, which can call mnt_clone_write
if the file is open for write.
After these two patches, mnt_want_write and mnt_drop_write go from 7% on
the profile down to 1.3% (including mnt_clone_write).
[AV: mnt_want_write_file() should take file alone and derive mnt from it;
not only all callers have that form, but that's the only mnt about which
we know that it's already held for write if file is opened for write]
Cc: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/file_table.c b/fs/file_table.c
index 54018fe..3d66dbc 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -214,7 +214,7 @@
*/
if ((mode & FMODE_WRITE) && !special_file(dentry->d_inode->i_mode)) {
file_take_write(file);
- error = mnt_want_write(mnt);
+ error = mnt_clone_write(mnt);
WARN_ON(error);
}
return error;
diff --git a/fs/inode.c b/fs/inode.c
index ca33701..a88baeb 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1422,7 +1422,7 @@
if (IS_NOCMTIME(inode))
return;
- err = mnt_want_write(file->f_path.mnt);
+ err = mnt_want_write_file(file);
if (err)
return;
diff --git a/fs/namespace.c b/fs/namespace.c
index 22ae06a..120b8a6 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -265,6 +265,46 @@
EXPORT_SYMBOL_GPL(mnt_want_write);
/**
+ * mnt_clone_write - get write access to a mount
+ * @mnt: the mount on which to take a write
+ *
+ * This is effectively like mnt_want_write, except
+ * it must only be used to take an extra write reference
+ * on a mountpoint that we already know has a write reference
+ * on it. This allows some optimisation.
+ *
+ * After finished, mnt_drop_write must be called as usual to
+ * drop the reference.
+ */
+int mnt_clone_write(struct vfsmount *mnt)
+{
+ /* superblock may be r/o */
+ if (__mnt_is_readonly(mnt))
+ return -EROFS;
+ preempt_disable();
+ inc_mnt_writers(mnt);
+ preempt_enable();
+ return 0;
+}
+EXPORT_SYMBOL_GPL(mnt_clone_write);
+
+/**
+ * mnt_want_write_file - get write access to a file's mount
+ * @file: the file who's mount on which to take a write
+ *
+ * This is like mnt_want_write, but it takes a file and can
+ * do some optimisations if the file is open for write already
+ */
+int mnt_want_write_file(struct file *file)
+{
+ if (!(file->f_mode & FMODE_WRITE))
+ return mnt_want_write(file->f_path.mnt);
+ else
+ return mnt_clone_write(file->f_path.mnt);
+}
+EXPORT_SYMBOL_GPL(mnt_want_write_file);
+
+/**
* mnt_drop_write - give up write access to a mount
* @mnt: the mount on which to give up write access
*
diff --git a/fs/open.c b/fs/open.c
index bdfbf03..7200e23 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -612,7 +612,7 @@
audit_inode(NULL, dentry);
- err = mnt_want_write(file->f_path.mnt);
+ err = mnt_want_write_file(file);
if (err)
goto out_putf;
mutex_lock(&inode->i_mutex);
@@ -761,7 +761,7 @@
if (!file)
goto out;
- error = mnt_want_write(file->f_path.mnt);
+ error = mnt_want_write_file(file);
if (error)
goto out_fput;
dentry = file->f_path.dentry;
diff --git a/fs/xattr.c b/fs/xattr.c
index d51b8f9..1c3d0af 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -297,7 +297,7 @@
return error;
dentry = f->f_path.dentry;
audit_inode(NULL, dentry);
- error = mnt_want_write(f->f_path.mnt);
+ error = mnt_want_write_file(f);
if (!error) {
error = setxattr(dentry, name, value, size, flags);
mnt_drop_write(f->f_path.mnt);
@@ -524,7 +524,7 @@
return error;
dentry = f->f_path.dentry;
audit_inode(NULL, dentry);
- error = mnt_want_write(f->f_path.mnt);
+ error = mnt_want_write_file(f);
if (!error) {
error = removexattr(dentry, name);
mnt_drop_write(f->f_path.mnt);