[PATCH 48/61] sysfs: use singly-linked list for sysfs_dirent tree

Greg Kroah-Hartman
2007-07-11T23:56:06Z

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>
---
fs/sysfs/dir.c | 146 +++++++++++++++++++++++++++++++++++++----------------
fs/sysfs/inode.c | 12 +++--
fs/sysfs/mount.c | 3 -
fs/sysfs/sysfs.h | 4 +-
4 files changed, 111 insertions(+), 54 deletions(-)

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 40596a0..b4074ad 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -22,6 +22,48 @@ static spinlock_t sysfs_ino_lock = SPIN_LOCK_UNLOCKED;
static DEFINE_IDA(sysfs_ino_ida);

/**
+ * sysfs_link_sibling - link sysfs_dirent into sibling list
+ * @sd: sysfs_dirent of interest
+ *
+ * Link @sd into its sibling list which starts from
+ * sd->s_parent->s_children.
+ *
+ * Locking:
+ * mutex_lock(sd->s_parent->dentry->d_inode->i_mutex)
+ */
+static void sysfs_link_sibling(struct sysfs_dirent *sd)
+{
+ struct sysfs_dirent *parent_sd = sd->s_parent;
+
+ BUG_ON(sd->s_sibling);
+ sd->s_sibling = parent_sd->s_children;
+ parent_sd->s_children = sd;
+}
+
+/**
+ * sysfs_unlink_sibling - unlink sysfs_dirent from sibling list
+ * @sd: sysfs_dirent of interest
+ *
+ * Unlink @sd from its sibling list which starts from
+ * sd->s_parent->s_children.
+ *
+ * Locking:
+ * mutex_lock(sd->s_parent->dentry->d_inode->i_mutex)
+ */
+static void sysfs_unlink_sibling(struct sysfs_dirent *sd)
+{
+ struct sysfs_dirent **pos;
+
+ for (pos = &sd->s_parent->s_children; *pos; pos = &(*pos)->s_sibling) {
+ if (*pos == sd) {
+ *pos = sd->s_sibling;
+ sd->s_sibling = NULL;
+ break;
+ }
+ }
+}
+
+/**
* sysfs_get_active - get an active reference to sysfs_dirent
* @sd: sysfs_dirent to get an active reference to
*
@@ -73,9 +115,9 @@ void sysfs_put_active(struct sysfs_dirent *sd)
return;

/* atomic_dec_return() is a mb(), we'll always see the updated
- * sd->s_sibling.next.
+ * sd->s_sibling.
*/
- cmpl = (void *)sd->s_sibling.next;
+ cmpl = (void *)sd->s_sibling;
complete(cmpl);
}

@@ -129,18 +171,18 @@ void sysfs_deactivate(struct sysfs_dirent *sd)
DECLARE_COMPLETION_ONSTACK(wait);
int v;

- BUG_ON(!list_empty(&sd->s_sibling));
- sd->s_sibling.next = (void *)&wait;
+ BUG_ON(sd->s_sibling);
+ sd->s_sibling = (void *)&wait;

/* atomic_add_return() is a mb(), put_active() will always see
- * the updated sd->s_sibling.next.
+ * the updated sd->s_sibling.
*/
v = atomic_add_return(SD_DEACTIVATED_BIAS, &sd->s_active);

if (v != SD_DEACTIVATED_BIAS)
wait_for_completion(&wait);

- INIT_LIST_HEAD(&sd->s_sibling);
+ sd->s_sibling = NULL;
}

static int sysfs_alloc_ino(ino_t *pino)
@@ -237,8 +279,6 @@ struct sysfs_dirent *sysfs_new_dirent(const char *name, umode_t mode, int type)
atomic_set(&sd->s_count, 1);
atomic_set(&sd->s_active, 0);
atomic_set(&sd->s_event, 1);
- INIT_LIST_HEAD(&sd->s_children);
- INIT_LIST_HEAD(&sd->s_sibling);

sd->s_name = name;
sd->s_mode = mode;
@@ -273,7 +313,7 @@ void sysfs_attach_dirent(struct sysfs_dirent *sd,

if (parent_sd) {
sd->s_parent = sysfs_get(parent_sd);
- list_add(&sd->s_sibling, &parent_sd->s_children);
+ sysfs_link_sibling(sd);
}
}

@@ -289,7 +329,7 @@ int sysfs_dirent_exist(struct sysfs_dirent *parent_sd,
{
struct sysfs_dirent * sd;

- list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
+ for (sd = parent_sd->s_children; sd; sd = sd->s_sibling) {
if (sd->s_type) {
if (strcmp(sd->s_name, new))
continue;
@@ -409,7 +449,7 @@ static struct dentry * sysfs_lookup(struct inode *dir, struct dentry *dentry,
struct inode *inode;
int found = 0;

- list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
+ for (sd = parent_sd->s_children; sd; sd = sd->s_sibling) {
if ((sd->s_type & SYSFS_NOT_PINNED) &&
!strcmp(sd->s_name, dentry->d_name.name)) {
found = 1;
@@ -458,7 +498,7 @@ static void remove_dir(struct dentry * d)

mutex_lock(&parent->d_inode->i_mutex);

- list_del_init(&sd->s_sibling);
+ sysfs_unlink_sibling(sd);

pr_debug(" o %s removing done (%d)\n",d->d_name.name,
atomic_read(&d->d_count));
@@ -478,9 +518,9 @@ void sysfs_remove_subdir(struct dentry * d)

static void __sysfs_remove_dir(struct dentry *dentry)
{
- LIST_HEAD(removed);
- struct sysfs_dirent * parent_sd;
- struct sysfs_dirent * sd, * tmp;
+ struct sysfs_dirent *removed = NULL;
+ struct sysfs_dirent *parent_sd;
+ struct sysfs_dirent **pos;

if (!dentry)
return;
@@ -488,15 +528,25 @@ static void __sysfs_remove_dir(struct dentry *dentry)
pr_debug("sysfs %s: removing dir\n",dentry->d_name.name);
mutex_lock(&dentry->d_inode->i_mutex);
parent_sd = dentry->d_fsdata;
- list_for_each_entry_safe(sd, tmp, &parent_sd->s_children, s_sibling) {
- if (!sd->s_type || !(sd->s_type & SYSFS_NOT_PINNED))
- continue;
- list_move(&sd->s_sibling, &removed);
+ pos = &parent_sd->s_children;
+ while (*pos) {
+ struct sysfs_dirent *sd = *pos;
+
+ if (sd->s_type && (sd->s_type & SYSFS_NOT_PINNED)) {
+ *pos = sd->s_sibling;
+ sd->s_sibling = removed;
+ removed = sd;
+ } else
+ pos = &(*pos)->s_sibling;
}
mutex_unlock(&dentry->d_inode->i_mutex);

- list_for_each_entry_safe(sd, tmp, &removed, s_sibling) {
- list_del_init(&sd->s_sibling);
+ while (removed) {
+ struct sysfs_dirent *sd = removed;
+
+ removed = sd->s_sibling;
+ sd->s_sibling = NULL;
+
sysfs_drop_dentry(sd);
sysfs_deactivate(sd);
sysfs_put(sd);
@@ -577,11 +627,11 @@ int sysfs_rename_dir(struct kobject * kobj, struct dentry *new_parent,
d_add(new_dentry, NULL);
d_move(kobj->dentry, new_dentry);

- list_del_init(&sd->s_sibling);
+ sysfs_unlink_sibling(sd);
sysfs_get(parent_sd);
sysfs_put(sd->s_parent);
sd->s_parent = parent_sd;
- list_add(&sd->s_sibling, &parent_sd->s_children);
+ sysfs_link_sibling(sd);

error = 0;
goto out_unlock;
@@ -633,11 +683,11 @@ again:
dput(new_dentry);

/* Remove from old parent's list and insert into new parent's list. */
- list_del_init(&sd->s_sibling);
+ sysfs_unlink_sibling(sd);
sysfs_get(new_parent_sd);
sysfs_put(sd->s_parent);
sd->s_parent = new_parent_sd;
- list_add(&sd->s_sibling, &new_parent_sd->s_children);
+ sysfs_link_sibling(sd);

out:
mutex_unlock(&new_parent_dentry->d_inode->i_mutex);
@@ -668,7 +718,7 @@ static int sysfs_dir_close(struct inode *inode, struct file *file)
struct sysfs_dirent * cursor = file->private_data;

mutex_lock(&dentry->d_inode->i_mutex);
- list_del_init(&cursor->s_sibling);
+ sysfs_unlink_sibling(cursor);
mutex_unlock(&dentry->d_inode->i_mutex);

release_sysfs_dirent(cursor);
@@ -687,7 +737,7 @@ static int sysfs_readdir(struct file * filp, void * dirent, filldir_t filldir)
struct dentry *dentry = filp->f_path.dentry;
struct sysfs_dirent * parent_sd = dentry->d_fsdata;
struct sysfs_dirent *cursor = filp->private_data;
- struct list_head *p, *q = &cursor->s_sibling;
+ struct sysfs_dirent **pos;
ino_t ino;
int i = filp->f_pos;

@@ -710,16 +760,21 @@ static int sysfs_readdir(struct file * filp, void * dirent, filldir_t filldir)
i++;
/* fallthrough */
default:
+ pos = &parent_sd->s_children;
+ while (*pos != cursor)
+ pos = &(*pos)->s_sibling;
+
+ /* unlink cursor */
+ *pos = cursor->s_sibling;
+
if (filp->f_pos == 2)
- list_move(q, &parent_sd->s_children);
+ pos = &parent_sd->s_children;

- for (p=q->next; p!= &parent_sd->s_children; p=p->next) {
- struct sysfs_dirent *next;
+ for ( ; *pos; pos = &(*pos)->s_sibling) {
+ struct sysfs_dirent *next = *pos;
const char * name;
int len;

- next = list_entry(p, struct sysfs_dirent,
- s_sibling);
if (!next->s_type)
continue;

@@ -729,12 +784,14 @@ static int sysfs_readdir(struct file * filp, void * dirent, filldir_t filldir)

if (filldir(dirent, name, len, filp->f_pos, ino,
dt_type(next)) < 0)
- return 0;
+ break;

- list_move(q, p);
- p = q;
filp->f_pos++;
}
+
+ /* put cursor back in */
+ cursor->s_sibling = *pos;
+ *pos = cursor;
}
return 0;
}
@@ -759,20 +816,21 @@ static loff_t sysfs_dir_lseek(struct file * file, loff_t offset, int origin)
if (file->f_pos >= 2) {
struct sysfs_dirent *sd = dentry->d_fsdata;
struct sysfs_dirent *cursor = file->private_data;
- struct list_head *p;
+ struct sysfs_dirent **pos;
loff_t n = file->f_pos - 2;

- list_del(&cursor->s_sibling);
- p = sd->s_children.next;
- while (n && p != &sd->s_children) {
- struct sysfs_dirent *next;
- next = list_entry(p, struct sysfs_dirent,
- s_sibling);
+ sysfs_unlink_sibling(cursor);
+
+ pos = &sd->s_children;
+ while (n && *pos) {
+ struct sysfs_dirent *next = *pos;
if (next->s_type)
n--;
- p = p->next;
+ pos = &(*pos)->s_sibling;
}
- list_add_tail(&cursor->s_sibling, p);
+
+ cursor->s_sibling = *pos;
+ *pos = cursor;
}
}
mutex_unlock(&dentry->d_inode->i_mutex);
diff --git a/fs/sysfs/inode.c b/fs/sysfs/inode.c
index 3eab9c4..732fd7f 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;
}
diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c
index d0e1603..4be9593 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,
};

diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index ae006b0..6f8aaf3 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 {
--
1.5.2.2