Re: [PATCH]: Making high and batch sizes of per_cpu_pagelists configurable

[Andrew Morton <akpm@osdl.org>]

Rohit Seth <rohit.seth@intel.com> wrote:
>
> +	if ((high/4) > (PAGE_SHIFT * 8))
>  +		pcp->batch = PAGE_SHIFT * 8;

hm.  What relationship is there between log2(PAGE_SIZE) and the batch
quantity?  I'd have thought that if anything, we'd want to make the batch
sizes smaller for larger PAGE_SIZE.  Or something.

>  +}
>  +
>  +/*
>  + * percpu_pagelist_fraction - changes the pcp->high for each zone on each
>  + * cpu.  It is the fraction of total pages in each zone that a hot per cpu pagelist
>  + * can have before it gets flushed back to buddy allocator.
>  + */
>  +
>  +int percpu_pagelist_fraction_sysctl_handler(ctl_table *table, int write,
>  +	struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
>  +{
>  +	struct zone *zone;
>  +	unsigned int cpu;
>  +	int ret;
>  +
>  +	ret = proc_dointvec_minmax(table, write, file, buffer, length, ppos);
>  +	if (!write || (ret == -EINVAL))
>  +		return ret;
>  +	for_each_zone(zone) {
>  +		for_each_online_cpu(cpu) {
>  +			unsigned long  high;
>  +			high = zone->present_pages / percpu_pagelist_fraction;
>  +			setup_pagelist_highmark(zone_pcp(zone, cpu), high);

What happens if a CPU comes online afterwards?