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, 0 insertions, 3 deletions

diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c
index d0e160307c5d..4be9593ea000 100644
--- a/fs/sysfs/mount.c
+++ b/fs/sysfs/mount.c
@@ -26,11 +26,8 @@ static const struct super_operations sysfs_ops = {
 
 static struct sysfs_dirent sysfs_root = {
         .s_count        = ATOMIC_INIT(1),
-        .s_sibling      = LIST_HEAD_INIT(sysfs_root.s_sibling),
-        .s_children     = LIST_HEAD_INIT(sysfs_root.s_children),
         .s_type         = SYSFS_ROOT,
         .s_mode         = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO,
-        .s_iattr        = NULL,
         .s_ino          = 1,
 };