Commit 96029c4e authored by npiggin@suse.de's avatar npiggin@suse.de Committed by Al Viro

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: default avatarNick Piggin <npiggin@suse.de>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent d3ef3d73
......@@ -214,7 +214,7 @@ int init_file(struct file *file, struct vfsmount *mnt, struct dentry *dentry,
*/
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;
......
......@@ -1422,7 +1422,7 @@ void file_update_time(struct file *file)
if (IS_NOCMTIME(inode))
return;
err = mnt_want_write(file->f_path.mnt);
err = mnt_want_write_file(file);
if (err)
return;
......
......@@ -264,6 +264,46 @@ out:
}
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
......
......@@ -612,7 +612,7 @@ SYSCALL_DEFINE2(fchmod, unsigned int, fd, mode_t, mode)
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 @@ SYSCALL_DEFINE3(fchown, unsigned int, fd, uid_t, user, gid_t, group)
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;
......
......@@ -297,7 +297,7 @@ SYSCALL_DEFINE5(fsetxattr, int, fd, const char __user *, name,
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 @@ SYSCALL_DEFINE2(fremovexattr, int, fd, const char __user *, name)
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);
......
......@@ -88,7 +88,11 @@ static inline struct vfsmount *mntget(struct vfsmount *mnt)
return mnt;
}
struct file; /* forward dec */
extern int mnt_want_write(struct vfsmount *mnt);
extern int mnt_want_write_file(struct file *file);
extern int mnt_clone_write(struct vfsmount *mnt);
extern void mnt_drop_write(struct vfsmount *mnt);
extern void mntput_no_expire(struct vfsmount *mnt);
extern void mnt_pin(struct vfsmount *mnt);
......
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