[PATCH] tvec_bases too large for per-cpu data

["Jan Beulich" <JBeulich@novell.com>]

[-- Attachment #1: Type: text/plain, Size: 621 bytes --]

From: Jan Beulich <jbeulich@novell.com>

With internal Xen-enabled kernels we see the kernel's static per-cpu
data area
exceed the limit of 32k on x86-64, and even native x86-64 kernels get
fairly
close to that limit. I generally question whether it is reasonable to
have
data structures several kb in size allocated as per-cpu data when the
space
there is rather limited.
The biggest arch-independent consumer is tvec_bases (over 4k on 32-bit
archs,
over 8k on 64-bit ones), which now gets converted to use dynamically
allocated
memory instead.

Signed-Off-By: Jan Beulich <jbeulich@novell.com>

(actual patch attached)

[-- Attachment #2: linux-2.6.16-rc1-per-cpu-tvec_bases.patch --]
[-- Type: application/octet-stream, Size: 4159 bytes --]

From: Jan Beulich <jbeulich@novell.com>

With internal Xen-enabled kernels we see the kernel's static per-cpu data area
exceed the limit of 32k on x86-64, and even native x86-64 kernels get fairly
close to that limit. I generally question whether it is reasonable to have
data structures several kb in size allocated as per-cpu data when the space
there is rather limited.
The biggest arch-independent consumer is tvec_bases (over 4k on 32-bit archs,
over 8k on 64-bit ones), which now gets converted to use dynamically allocated
memory instead.

Signed-Off-By: Jan Beulich <jbeulich@novell.com>

diff -Npru /home/jbeulich/tmp/linux-2.6.16-rc1/kernel/timer.c 2.6.16-rc1-per-cpu-tvec_bases/kernel/timer.c
--- /home/jbeulich/tmp/linux-2.6.16-rc1/kernel/timer.c	2006-01-18 12:39:13.000000000 +0100
+++ 2.6.16-rc1-per-cpu-tvec_bases/kernel/timer.c	2006-01-18 13:53:28.000000000 +0100
@@ -86,7 +86,8 @@ struct tvec_t_base_s {
 } ____cacheline_aligned_in_smp;
 
 typedef struct tvec_t_base_s tvec_base_t;
-static DEFINE_PER_CPU(tvec_base_t, tvec_bases);
+static DEFINE_PER_CPU(tvec_base_t *, tvec_bases);
+static tvec_base_t boot_tvec_bases;
 
 static inline void set_running_timer(tvec_base_t *base,
 					struct timer_list *timer)
@@ -157,7 +158,7 @@ EXPORT_SYMBOL(__init_timer_base);
 void fastcall init_timer(struct timer_list *timer)
 {
 	timer->entry.next = NULL;
-	timer->base = &per_cpu(tvec_bases, raw_smp_processor_id()).t_base;
+	timer->base = &per_cpu(tvec_bases, raw_smp_processor_id())->t_base;
 }
 EXPORT_SYMBOL(init_timer);
 
@@ -218,7 +219,7 @@ int __mod_timer(struct timer_list *timer
 		ret = 1;
 	}
 
-	new_base = &__get_cpu_var(tvec_bases);
+	new_base = __get_cpu_var(tvec_bases);
 
 	if (base != &new_base->t_base) {
 		/*
@@ -258,7 +259,7 @@ EXPORT_SYMBOL(__mod_timer);
  */
 void add_timer_on(struct timer_list *timer, int cpu)
 {
-	tvec_base_t *base = &per_cpu(tvec_bases, cpu);
+	tvec_base_t *base = per_cpu(tvec_bases, cpu);
   	unsigned long flags;
 
   	BUG_ON(timer_pending(timer) || !timer->function);
@@ -492,7 +493,7 @@ unsigned long next_timer_interrupt(void)
 	tvec_t *varray[4];
 	int i, j;
 
-	base = &__get_cpu_var(tvec_bases);
+	base = __get_cpu_var(tvec_bases);
 	spin_lock(&base->t_base.lock);
 	expires = base->timer_jiffies + (LONG_MAX >> 1);
 	list = 0;
@@ -856,7 +857,7 @@ EXPORT_SYMBOL(xtime_lock);
  */
 static void run_timer_softirq(struct softirq_action *h)
 {
-	tvec_base_t *base = &__get_cpu_var(tvec_bases);
+	tvec_base_t *base = __get_cpu_var(tvec_bases);
 
  	hrtimer_run_queues();
 	if (time_after_eq(jiffies, base->timer_jiffies))
@@ -1209,12 +1210,31 @@ asmlinkage long sys_sysinfo(struct sysin
 	return 0;
 }
 
-static void __devinit init_timers_cpu(int cpu)
+static int __devinit init_timers_cpu(int cpu)
 {
 	int j;
 	tvec_base_t *base;
 
-	base = &per_cpu(tvec_bases, cpu);
+	base = per_cpu(tvec_bases, cpu);
+	if (likely(!base)) {
+		static char boot_done;
+
+		if (likely(boot_done)) {
+#ifdef CONFIG_NUMA
+			base = kmalloc_node(sizeof(*base), GFP_KERNEL, cpu_to_node(cpu));
+			if (!base)
+#endif
+				base = kmalloc(sizeof(*base), GFP_KERNEL);
+			if (!base)
+				return -ENOMEM;
+			memset(base, 0, sizeof(*base));
+		}
+		else {
+			base = &boot_tvec_bases;
+			boot_done = 1;
+		}
+		per_cpu(tvec_bases, cpu) = base;
+	}
 	spin_lock_init(&base->t_base.lock);
 	for (j = 0; j < TVN_SIZE; j++) {
 		INIT_LIST_HEAD(base->tv5.vec + j);
@@ -1226,6 +1246,7 @@ static void __devinit init_timers_cpu(in
 		INIT_LIST_HEAD(base->tv1.vec + j);
 
 	base->timer_jiffies = jiffies;
+	return 0;
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
@@ -1248,8 +1269,8 @@ static void __devinit migrate_timers(int
 	int i;
 
 	BUG_ON(cpu_online(cpu));
-	old_base = &per_cpu(tvec_bases, cpu);
-	new_base = &get_cpu_var(tvec_bases);
+	old_base = per_cpu(tvec_bases, cpu);
+	new_base = get_cpu_var(tvec_bases);
 
 	local_irq_disable();
 	spin_lock(&new_base->t_base.lock);
@@ -1279,7 +1300,8 @@ static int __devinit timer_cpu_notify(st
 	long cpu = (long)hcpu;
 	switch(action) {
 	case CPU_UP_PREPARE:
-		init_timers_cpu(cpu);
+		if (init_timers_cpu(cpu) < 0)
+			return NOTIFY_BAD;
 		break;
 #ifdef CONFIG_HOTPLUG_CPU
 	case CPU_DEAD: