cpumask: add nr_cpumask_bits When nr_cpu_ids is set to CONFIG_NR_CPUS then references to nr_cpu_ids will return the maximum index of the configured NR_CPUS (+1) instead of the maximum index of the possible number of cpus (+1). This results in extra unused memory being allocated by functions that are setting up arrays of structs to keep track of per cpu items. Since we do want to keep the ability to use constants for the cpu bit operators on smaller systems (which are generally much faster assembler ops), we introduce a separate "nr_cpumask_bits" to replace "nr_cpu_ids" only for the inline assembly ops. This will be a constant when CONFIG_CPUMASK_OFFSTACK is undefined and a variable when it is defined. Thus "nr_cpu_ids" reverts back to being a variable representing the maximum possible cpu (+1), except in the non-SMP case where it is a constant value of 1. The relationship between the related variables and constants is: (1 <= nr_cpu_ids <= nr_cpumask_bits <= NR_CPUS). Signed-of-by: Mike Travis --- arch/x86/kernel/setup_percpu.c | 7 ++++--- include/linux/cpumask.h | 8 ++++++++ 2 files changed, 12 insertions(+), 3 deletions(-) diff -r 4106f6225184 arch/x86/kernel/setup_percpu.c --- a/arch/x86/kernel/setup_percpu.c Wed Oct 22 10:43:16 2008 +1100 +++ b/arch/x86/kernel/setup_percpu.c Wed Oct 22 10:46:16 2008 +1100 @@ -155,6 +155,10 @@ void __init setup_per_cpu_areas(void) printk(KERN_INFO "PERCPU: Allocating %zd bytes of per cpu data\n", size); + printk(KERN_DEBUG + "NR_CPUS:%d nr_cpumask_bits:%d nr_cpu_ids:%d nr_node_ids:%d\n", + NR_CPUS, nr_cpumask_bits, nr_cpu_ids, nr_node_ids); + for_each_possible_cpu(cpu) { #ifndef CONFIG_NEED_MULTIPLE_NODES ptr = __alloc_bootmem(size, align, @@ -182,9 +186,6 @@ void __init setup_per_cpu_areas(void) per_cpu_offset(cpu) = ptr - __per_cpu_start; memcpy(ptr, __per_cpu_start, __per_cpu_end - __per_cpu_start); } - - printk(KERN_DEBUG "NR_CPUS: %d, nr_cpu_ids: %d, nr_node_ids %d\n", - NR_CPUS, nr_cpu_ids, nr_node_ids); /* Setup percpu data maps */ setup_per_cpu_maps(); diff -r 4106f6225184 include/linux/cpumask.h --- a/include/linux/cpumask.h Wed Oct 22 10:43:16 2008 +1100 +++ b/include/linux/cpumask.h Wed Oct 22 10:46:16 2008 +1100 @@ -199,6 +199,14 @@ extern int nr_cpu_ids; extern int nr_cpu_ids; #else #define nr_cpu_ids NR_CPUS +#endif + +/* The number of bits to hand to the bitmask ops. */ +#if NR_CPUS <= BITS_PER_LONG +/* This produces more efficient code. */ +#define nr_cpumask_bits NR_CPUS +#else +#define nr_cpumask_bits nr_cpu_ids #endif static inline void cpumask_set_cpu(int cpu, volatile struct cpumask *dstp)