From: Maneesh Soni <maneesh@in.ibm.com>

o This patch stops the pinning of non-directory or leaf dentries and inodes.
  The leaf dentries and inodes are created during lookup based on the
  entries on sysfs_dirent tree. These leaves are removed from the dcache
  through the VFS dentry ageing process during shrink dcache operations. Thus
  reducing about 80% of sysfs lowmem needs.

o This implments the ->lookup() for sysfs directory inodes and allocates
  dentry and inode if the lookup is successful and avoids the need of
  allocating and pinning of dentry and inodes during the creation of
  corresponding sysfs leaf entry. As of now the implementation has not
  required negative dentry creation on failed lookup. As sysfs is still a
  RAM based filesystem, negative dentries are not of any use IMO.

o The leaf dentry allocated after successful lookup is connected to the
  existing corresponding sysfs_dirent through the d_fsdata field.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>