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, 7 insertions, 5 deletions

diff --git a/fs/sysfs/inode.c b/fs/sysfs/inode.c
index 3eab9c46a71b..732fd7f371e0 100644
--- a/fs/sysfs/inode.c
+++ b/fs/sysfs/inode.c
@@ -284,8 +284,8 @@ void sysfs_drop_dentry(struct sysfs_dirent *sd)
 
 int sysfs_hash_and_remove(struct dentry * dir, const char * name)
 {
-        struct sysfs_dirent * sd;
-        struct sysfs_dirent * parent_sd;
+        struct sysfs_dirent **pos, *sd;
+        struct sysfs_dirent *parent_sd = dir->d_fsdata;
         int found = 0;
 
         if (!dir)
@@ -295,13 +295,15 @@ int sysfs_hash_and_remove(struct dentry * dir, const char * name)
                 /* no inode means this hasn't been made visible yet */
                 return -ENOENT;
 
-        parent_sd = dir->d_fsdata;
         mutex_lock_nested(&dir->d_inode->i_mutex, I_MUTEX_PARENT);
-        list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
+        for (pos = &parent_sd->s_children; *pos; pos = &(*pos)->s_sibling) {
+                sd = *pos;
+
                 if (!sd->s_type)
                         continue;
                 if (!strcmp(sd->s_name, name)) {
-                        list_del_init(&sd->s_sibling);
+                        *pos = sd->s_sibling;
+                        sd->s_sibling = NULL;
                         found = 1;
                         break;
                 }