irq: allocate irq_desc_ptrs array based on nr_irqs

Impact: allocate irq_desc_ptrs in preparation for making it variable-sized.

This addresses this memory usage bump when NR_CPUS bumped from 128 to 4096:

    34816   +229376    264192  +658%  irq_desc_ptrs(.data.read_mostly)

The patch is split into two parts, the first simply allocates the
irq_desc_ptrs array.  Then next will deal with making it variable.
This is only when CONFIG_SPARSE_IRQS=y.

Signed-off-by: Mike Travis <travis@sgi.com>

1 files changed, 9 insertions, 2 deletions

diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c
index fd1ef16252f4..d0b8f7e72790 100644
--- a/kernel/irq/handle.c
+++ b/kernel/irq/handle.c
@@ -17,6 +17,7 @@
 #include <linux/kernel_stat.h>
 #include <linux/rculist.h>
 #include <linux/hash.h>
+#include <linux/bootmem.h>
 
 #include "internals.h"
 
@@ -110,7 +111,7 @@ static void init_one_irq_desc(int irq, struct irq_desc *desc, int cpu)
  */
 DEFINE_SPINLOCK(sparse_irq_lock);
 
-struct irq_desc *irq_desc_ptrs[NR_IRQS] __read_mostly;
+struct irq_desc **irq_desc_ptrs __read_mostly;
 
 static struct irq_desc irq_desc_legacy[NR_IRQS_LEGACY] __cacheline_aligned_in_smp = {
         [0 ... NR_IRQS_LEGACY-1] = {
@@ -137,6 +138,9 @@ int __init early_irq_init(void)
         desc = irq_desc_legacy;
         legacy_count = ARRAY_SIZE(irq_desc_legacy);
 
+        /* allocate irq_desc_ptrs array based on nr_irqs */
+        irq_desc_ptrs = alloc_bootmem(nr_irqs * sizeof(void *));
+
         for (i = 0; i < legacy_count; i++) {
                 desc[i].irq = i;
                 desc[i].kstat_irqs = kstat_irqs_legacy[i];
@@ -153,7 +157,10 @@ int __init early_irq_init(void)
 
 struct irq_desc *irq_to_desc(unsigned int irq)
 {
-        return (irq < nr_irqs) ? irq_desc_ptrs[irq] : NULL;
+        if (irq_desc_ptrs && irq < nr_irqs)
+                return irq_desc_ptrs[irq];
+
+        return NULL;
 }
 
 struct irq_desc *irq_to_desc_alloc_cpu(unsigned int irq, int cpu)