[PATCH v2] core-parking: shrink core_parking_cpunum[]

[Jan Beulich <jbeulich@xxxxxxxx>]

This NR_CPUS-dimensioned array is likely unused on most installations.
Therefore it is especially wasteful for it to consume more space than
really needed. Allocate it dynamically ahead of registering the hooks.

Further the array having all fields set to -1 is actually useless. Nothing
relies on it, and core_parking_remove() doesn't restore the sentinel for
vacated slots. Drop the initializers altogether, rather than replacing
them.

Also take the opportunity and update an adjacent variable's type, where
a fixed-width type was pretty clearly inappropriate to use.

Finally drop the redundant initializer from core_parking_init().

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
I assume there is a reason this is acting (mostly) as a LIFO. Else a
simple cpumask_t would suffice.

num_possible_cpus() would be the more correct thing to use as array
dimension, yet we don't maintain cpu_possible_map on x86.
---
v2: Use dynamic allocation.

--- a/xen/common/core_parking.c
+++ b/xen/common/core_parking.c
@@ -20,6 +20,7 @@
 #include <xen/cpumask.h>
 #include <xen/init.h>
 #include <xen/param.h>
+#include <xen/xvmalloc.h>
 
 #include <asm/smp.h>
 
@@ -27,8 +28,8 @@
 #define CORE_PARKING_DECREMENT 2
 
 static DEFINE_SPINLOCK(accounting_lock);
-static uint32_t cur_idle_nums;
-static unsigned int core_parking_cpunum[NR_CPUS] = {[0 ... NR_CPUS-1] = -1};
+static unsigned int cur_idle_nums;
+static unsigned int *__ro_after_init core_parking_cpunum;
 
 struct cp_policy {
     char name[30];
@@ -188,7 +189,7 @@ long cf_check core_parking_helper(void *
             return ret;
 
         spin_lock(&accounting_lock);
-        BUG_ON(cur_idle_nums >= ARRAY_SIZE(core_parking_cpunum));
+        BUG_ON(cur_idle_nums >= nr_cpu_ids);
         core_parking_cpunum[cur_idle_nums++] = cpu;
         spin_unlock(&accounting_lock);
     }
@@ -263,9 +264,12 @@ static int __init register_core_parking_
 
 static int __init cf_check core_parking_init(void)
 {
-    int ret = 0;
+    int ret;
 
-    if ( core_parking_controller == PERFORMANCE_FIRST )
+    core_parking_cpunum = xvzalloc_array(unsigned int, nr_cpu_ids);
+    if ( !core_parking_cpunum )
+        ret = -ENOMEM;
+    else if ( core_parking_controller == PERFORMANCE_FIRST )
         ret = register_core_parking_policy(&performance_first);
     else
         ret = register_core_parking_policy(&power_first);