[PATCH] tvec_bases too large for per-cpu data

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>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/kernel/timer.c b/kernel/timer.c
index 2410c18..4427e72 100644 (file)
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -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, unsigned long expires)
                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);
@@ -504,7 +505,7 @@ unsigned long next_timer_interrupt(void)
        }
        hr_expires += jiffies;
 
-       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 = NULL;
@@ -901,7 +902,7 @@ 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))
@@ -1256,12 +1257,32 @@ asmlinkage long sys_sysinfo(struct sysinfo __user *info)
        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 (!base) {
+               static char boot_done;
+
+               /*
+                * Cannot do allocation in init_timers as that runs before the
+                * allocator initializes (and would waste memory if there are
+                * more possible CPUs than will ever be installed/brought up).
+                */
+               if (boot_done) {
+                       base = kmalloc_node(sizeof(*base), GFP_KERNEL,
+                                               cpu_to_node(cpu));
+                       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);
@@ -1273,6 +1294,7 @@ static void __devinit init_timers_cpu(int cpu)
                INIT_LIST_HEAD(base->tv1.vec + j);
 
        base->timer_jiffies = jiffies;
+       return 0;
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
@@ -1295,8 +1317,8 @@ static void __devinit migrate_timers(int cpu)
        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);
@@ -1326,7 +1348,8 @@ static int __devinit timer_cpu_notify(struct notifier_block *self,
        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: