Messages in this thread | | | From | KOSAKI Motohiro <> | Subject | Re: [PATCH 2/3] mm: page allocator: Calculate a better estimate of NR_FREE_PAGES when memory is low and kswapd is awake | Date | Wed, 1 Sep 2010 08:37:41 +0900 (JST) |
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> +#ifdef CONFIG_SMP > +/* Called when a more accurate view of NR_FREE_PAGES is needed */ > +unsigned long zone_nr_free_pages(struct zone *zone) > +{ > + unsigned long nr_free_pages = zone_page_state(zone, NR_FREE_PAGES); > + > + /* > + * While kswapd is awake, it is considered the zone is under some > + * memory pressure. Under pressure, there is a risk that > + * per-cpu-counter-drift will allow the min watermark to be breached > + * potentially causing a live-lock. While kswapd is awake and > + * free pages are low, get a better estimate for free pages > + */ > + if (nr_free_pages < zone->percpu_drift_mark && > + !waitqueue_active(&zone->zone_pgdat->kswapd_wait)) { > + int cpu; > + > + for_each_online_cpu(cpu) { > + struct per_cpu_pageset *pset; > + > + pset = per_cpu_ptr(zone->pageset, cpu); > + nr_free_pages += pset->vm_stat_diff[NR_FREE_PAGES];
If my understanding is correct, we have no lock when reading pset->vm_stat_diff. It mean nr_free_pages can reach negative value at very rarely race. boundary check is necessary?
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