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). Cc: Dave Hansen Signed-off-by: Nick Piggin --- fs/file_table.c | 3 +-- fs/inode.c | 2 +- fs/namespace.c | 38 ++++++++++++++++++++++++++++++++++++++ fs/open.c | 4 ++-- fs/xattr.c | 4 ++-- include/linux/mount.h | 4 ++++ 6 files changed, 48 insertions(+), 7 deletions(-) Index: linux-2.6/fs/file_table.c =================================================================== --- linux-2.6.orig/fs/file_table.c +++ linux-2.6/fs/file_table.c @@ -217,8 +217,7 @@ int init_file(struct file *file, struct */ if ((mode & FMODE_WRITE) && !special_file(dentry->d_inode->i_mode)) { file_take_write(file); - error = mnt_want_write(mnt); - WARN_ON(error); + mnt_clone_write(mnt); } return error; } Index: linux-2.6/fs/inode.c =================================================================== --- linux-2.6.orig/fs/inode.c +++ linux-2.6/fs/inode.c @@ -1401,7 +1401,7 @@ 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->f_path.mnt, file); if (err) return; Index: linux-2.6/fs/namespace.c =================================================================== --- linux-2.6.orig/fs/namespace.c +++ linux-2.6/fs/namespace.c @@ -265,6 +265,44 @@ 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. + */ +void mnt_clone_write(struct vfsmount *mnt) +{ + preempt_disable(); + inc_mnt_writers(mnt); + preempt_enable(); +} +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 vfsmount *mnt, struct file *file) +{ + if (!(file->f_mode & FMODE_WRITE)) + return mnt_want_write(mnt); + else { + mnt_clone_write(mnt); + return 0; + } +} +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 * Index: linux-2.6/fs/open.c =================================================================== --- linux-2.6.orig/fs/open.c +++ linux-2.6/fs/open.c @@ -612,7 +612,7 @@ SYSCALL_DEFINE2(fchmod, unsigned int, fd audit_inode(NULL, dentry); - err = mnt_want_write(file->f_path.mnt); + err = mnt_want_write_file(file->f_path.mnt, file); if (err) goto out_putf; mutex_lock(&inode->i_mutex); @@ -761,7 +761,7 @@ SYSCALL_DEFINE3(fchown, unsigned int, fd if (!file) goto out; - error = mnt_want_write(file->f_path.mnt); + error = mnt_want_write_file(file->f_path.mnt, file); if (error) goto out_fput; dentry = file->f_path.dentry; Index: linux-2.6/fs/xattr.c =================================================================== --- linux-2.6.orig/fs/xattr.c +++ linux-2.6/fs/xattr.c @@ -297,7 +297,7 @@ SYSCALL_DEFINE5(fsetxattr, int, fd, cons 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->f_path.mnt, 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, c 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->f_path.mnt, f); if (!error) { error = removexattr(dentry, name); mnt_drop_write(f->f_path.mnt); Index: linux-2.6/include/linux/mount.h =================================================================== --- linux-2.6.orig/include/linux/mount.h +++ linux-2.6/include/linux/mount.h @@ -88,7 +88,11 @@ static inline struct vfsmount *mntget(st return mnt; } +struct file; /* forward dec */ + extern int mnt_want_write(struct vfsmount *mnt); +extern int mnt_want_write_file(struct vfsmount *mnt, struct file *file); +extern void 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); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/