[PATCH] shrink task_struct by 16 bytes

From: Davi Arnaut
Date: Sat May 19 2007 - 23:40:32 EST

Hi,

Shrink task_struct by replacing the notifier callback with a
notifier list. The block_all_signals() function (and the signal
notifier mechanism) has only one user at the moment, which is drm.

Pahole output for task_struct:

i386 before:

/* size: 2640, cachelines: 42 */
/* sum members: 2619, holes: 3, sum holes: 9 */
/* bit holes: 2, sum bit holes: 62 bits */
/* padding: 12 */
/* paddings: 1, sum paddings: 8 */
/* last cacheline: 16 bytes */

i386 after:

/* size: 2624, cachelines: 41 */
/* sum members: 2615, holes: 3, sum holes: 9 */
/* bit holes: 2, sum bit holes: 62 bits */
/* paddings: 1, sum paddings: 8 */

x86_64 before:

/* size: 3648, cachelines: 57 */
/* sum members: 3587, holes: 13, sum holes: 53 */
/* bit holes: 2, sum bit holes: 62 bits */
/* padding: 8 */

x86_64 after:

/* size: 3632, cachelines: 57 */
/* sum members: 3579, holes: 13, sum holes: 53 */
/* bit holes: 2, sum bit holes: 62 bits */
/* last cacheline: 48 bytes */

Signed-off-by: Davi E. M. Arnaut <davi@xxxxxxxxxxxxx>

---
drivers/char/drm/drmP.h | 4 ++--
drivers/char/drm/drm_lock.c | 16 +++++++++-------
include/linux/init_task.h | 1 +
include/linux/sched.h | 12 +++++-------
include/linux/signal.h | 16 ++++++++++++++++
kernel/fork.c | 1 +
kernel/signal.c | 42 ++++++++++++++++++++----------------------
7 files changed, 54 insertions(+), 38 deletions(-)

Index: linux-2.6/include/linux/sched.h
===================================================================
--- linux-2.6.orig/include/linux/sched.h
+++ linux-2.6/include/linux/sched.h
@@ -963,10 +963,9 @@ struct task_struct {

unsigned long sas_ss_sp;
size_t sas_ss_size;
- int (*notifier)(void *priv);
- void *notifier_data;
- sigset_t *notifier_mask;
-
+ /* signal notifier list */
+ struct list_head notifier_list;
+
void *security;
struct audit_context *audit_context;
seccomp_t seccomp;
@@ -1339,9 +1338,8 @@ static inline int dequeue_signal_lock(st
return ret;
}

-extern void block_all_signals(int (*notifier)(void *priv), void *priv,
- sigset_t *mask);
-extern void unblock_all_signals(void);
+extern void block_signals(struct signal_notifier *);
+extern void unblock_signals(struct signal_notifier *);
extern void release_task(struct task_struct * p);
extern int send_sig_info(int, struct siginfo *, struct task_struct *);
extern int send_group_sig_info(int, struct siginfo *, struct task_struct *);
Index: linux-2.6/include/linux/init_task.h
===================================================================
--- linux-2.6.orig/include/linux/init_task.h
+++ linux-2.6/include/linux/init_task.h
@@ -157,6 +157,7 @@ extern struct group_info init_groups;
.list = LIST_HEAD_INIT(tsk.pending.list), \
.signal = {{0}}}, \
.blocked = {{0}}, \
+ .notifier_list = LIST_HEAD_INIT(tsk.notifier_list), \
.alloc_lock = __SPIN_LOCK_UNLOCKED(tsk.alloc_lock), \
.journal_info = NULL, \
.cpu_timers = INIT_CPU_TIMERS(tsk.cpu_timers), \
Index: linux-2.6/include/linux/signal.h
===================================================================
--- linux-2.6.orig/include/linux/signal.h
+++ linux-2.6/include/linux/signal.h
@@ -27,6 +27,22 @@ struct sigpending {
sigset_t signal;
};

+/**
+ * struct signal_notifier - the signal notifier struct
+ * @list: list head to enqueue into the process notifier list
+ * @func: notifier callback function. if the callback routine returns 0
+ * then then signal will be blocked.
+ * @data: pointer to private data that the notifier routine can use to
+ * determine if the signal should be blocked or not.
+ * @mask: mask of signals to call the callback routine upon
+ */
+struct signal_notifier {
+ struct list_head list;
+ int (*func)(void *priv);
+ void *data;
+ sigset_t mask;
+};
+
/*
* Define some primitives to manipulate sigset_t.
*/
Index: linux-2.6/kernel/fork.c
===================================================================
--- linux-2.6.orig/kernel/fork.c
+++ linux-2.6/kernel/fork.c
@@ -1034,6 +1034,7 @@ static struct task_struct *copy_process(
p->vfork_done = NULL;
spin_lock_init(&p->alloc_lock);

+ INIT_LIST_HEAD(&p->notifier_list);
clear_tsk_thread_flag(p, TIF_SIGPENDING);
init_sigpending(&p->pending);

Index: linux-2.6/drivers/char/drm/drm_lock.c
===================================================================
--- linux-2.6.orig/drivers/char/drm/drm_lock.c
+++ linux-2.6/drivers/char/drm/drm_lock.c
@@ -110,14 +110,16 @@ int drm_lock(struct inode *inode, struct
DRM_DEBUG( "%d %s\n", lock.context, ret ? "interrupted" : "has lock" );
if (ret) return ret;

- sigemptyset(&dev->sigmask);
- sigaddset(&dev->sigmask, SIGSTOP);
- sigaddset(&dev->sigmask, SIGTSTP);
- sigaddset(&dev->sigmask, SIGTTIN);
- sigaddset(&dev->sigmask, SIGTTOU);
+ sigemptyset(&dev->notifier.mask);
+ sigaddset(&dev->notifier.mask, SIGSTOP);
+ sigaddset(&dev->notifier.mask, SIGTSTP);
+ sigaddset(&dev->notifier.mask, SIGTTIN);
+ sigaddset(&dev->notifier.mask, SIGTTOU);
dev->sigdata.context = lock.context;
dev->sigdata.lock = dev->lock.hw_lock;
- block_all_signals(drm_notifier, &dev->sigdata, &dev->sigmask);
+ dev->notifier.data = &dev->sigdata;
+ dev->notifier.func = drm_notifier;
+ block_signals(&dev->notifier);

if (dev->driver->dma_ready && (lock.flags & _DRM_LOCK_READY))
dev->driver->dma_ready(dev);
@@ -189,7 +191,7 @@ int drm_unlock(struct inode *inode, stru
}
}

- unblock_all_signals();
+ unblock_signals(&dev->notifier);
return 0;
}

Index: linux-2.6/drivers/char/drm/drmP.h
===================================================================
--- linux-2.6.orig/drivers/char/drm/drmP.h
+++ linux-2.6/drivers/char/drm/drmP.h
@@ -750,8 +750,8 @@ typedef struct drm_device {
drm_sg_mem_t *sg; /**< Scatter gather memory */
unsigned long *ctx_bitmap; /**< context bitmap */
void *dev_private; /**< device private data */
- drm_sigdata_t sigdata; /**< For block_all_signals */
- sigset_t sigmask;
+ drm_sigdata_t sigdata; /**< Signal notifier data */
+ struct signal_notifier notifier; /**< For block_signals */

struct drm_driver *driver;
drm_local_map_t *agp_buffer_map;
Index: linux-2.6/kernel/signal.c
===================================================================
--- linux-2.6.orig/kernel/signal.c
+++ linux-2.6/kernel/signal.c
@@ -242,32 +242,28 @@ flush_signal_handlers(struct task_struct
* process, and wants to be notified if any signals at all were to be
* sent/acted upon. If the notifier routine returns non-zero, then the
* signal will be acted upon after all. If the notifier routine returns 0,
- * then then signal will be blocked. Only one block per process is
- * allowed. priv is a pointer to private data that the notifier routine
- * can use to determine if the signal should be blocked or not. */
+ * the signal will be blocked.
+ */

void
-block_all_signals(int (*notifier)(void *priv), void *priv, sigset_t *mask)
+block_signals(struct signal_notifier *notifier)
{
unsigned long flags;

spin_lock_irqsave(&current->sighand->siglock, flags);
- current->notifier_mask = mask;
- current->notifier_data = priv;
- current->notifier = notifier;
+ list_add_tail(&notifier->list, &current->notifier_list);
spin_unlock_irqrestore(&current->sighand->siglock, flags);
}

/* Notify the system that blocking has ended. */

void
-unblock_all_signals(void)
+unblock_signals(struct signal_notifier *notifier)
{
unsigned long flags;

spin_lock_irqsave(&current->sighand->siglock, flags);
- current->notifier = NULL;
- current->notifier_data = NULL;
+ list_del(&notifier->list);
recalc_sigpending();
spin_unlock_irqrestore(&current->sighand->siglock, flags);
}
@@ -318,22 +314,24 @@ static int collect_signal(int sig, struc
static int __dequeue_signal(struct sigpending *pending, sigset_t *mask,
siginfo_t *info)
{
+ struct signal_notifier *tmp, *notifier;
int sig = next_signal(pending, mask);

- if (sig) {
- if (current->notifier) {
- if (sigismember(current->notifier_mask, sig)) {
- if (!(current->notifier)(current->notifier_data)) {
- clear_thread_flag(TIF_SIGPENDING);
- return 0;
- }
+ if (unlikely(!sig))
+ return 0;
+
+ list_for_each_entry_safe(notifier, tmp, &current->notifier_list, list) {
+ if (sigismember(&notifier->mask, sig)) {
+ if (!(notifier->func)(notifier->data)) {
+ clear_thread_flag(TIF_SIGPENDING);
+ return 0;
}
}
-
- if (!collect_signal(sig, pending, info))
- sig = 0;
}

+ if (!collect_signal(sig, pending, info))
+ sig = 0;
+
return sig;
}

@@ -1860,8 +1858,8 @@ EXPORT_SYMBOL(ptrace_notify);
EXPORT_SYMBOL(send_sig);
EXPORT_SYMBOL(send_sig_info);
EXPORT_SYMBOL(sigprocmask);
-EXPORT_SYMBOL(block_all_signals);
-EXPORT_SYMBOL(unblock_all_signals);
+EXPORT_SYMBOL(block_signals);
+EXPORT_SYMBOL(unblock_signals);


/*
-
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