Re: [PATCH v3 5/5] mm: Only IPI CPUs to drain local pages if they exist

[Christoph Lameter <cl@linux.com>]

On Sun, 13 Nov 2011, Gilad Ben-Yossef wrote:

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 9dd443d..44dc6c5 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1119,7 +1119,23 @@ void drain_local_pages(void *arg)
>   */
>  void drain_all_pages(void)
>  {
> -	on_each_cpu(drain_local_pages, NULL, 1);
> +	int cpu;
> +	struct zone *zone;
> +	cpumask_var_t cpus;
> +	struct per_cpu_pageset *pageset;

We usually name such pointers "pcp" in the page allocator.

> +
> +	if (likely(zalloc_cpumask_var(&cpus, GFP_ATOMIC))) {
> +		for_each_populated_zone(zone) {
> +			for_each_online_cpu(cpu) {
> +				pageset = per_cpu_ptr(zone->pageset, cpu);
> +				if (pageset->pcp.count)
> +					cpumask_set_cpu(cpu, cpus);
> +		}

The pagesets are allocated on bootup from the per cpu areas. You may get a
better access pattern by using for_each_online_cpu as the outer loop
because their is a likelyhood of linear increasing accesses as you loop
through the zones for a particular cpu.

Acked-by: Christoph Lameter <cl@linux.com>

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