sysfs: use singly-linked list for sysfs_dirent tree

Make sysfs_dirent use singly linked list for its tree structure.
sysfs_link_sibling() and sysfs_unlink_sibling() functions are added to
handle simpler cases.  It adds some complexity and cpu cycle overhead
but reduced memory footprint is worthwhile on big machines.

This change reduces the sizeof sysfs_dirent from 104 to 88 on 64bit
and from 60 to 52 on 32bit.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index ae006b070bf0..6f8aaf3805d2 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -23,8 +23,8 @@ struct sysfs_dirent {
         atomic_t                s_count;
         atomic_t                s_active;
         struct sysfs_dirent     * s_parent;
-        struct list_head        s_sibling;
-        struct list_head        s_children;
+        struct sysfs_dirent     * s_sibling;
+        struct sysfs_dirent     * s_children;
         const char              * s_name;
 
         union {