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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: balbir@linux.vnet.ibm.com
Subject: Re: meminfo Committed_AS underflows
Cc: kosaki.motohiro@jp.fujitsu.com, Dave Hansen <dave@linux.vnet.ibm.com>,
       linux-mm <linux-mm@kvack.org>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       Eric B Munson <ebmunson@us.ibm.com>,
       Mel Gorman <mel@linux.vnet.ibm.com>,
       Christoph Lameter <cl@linux-foundation.org>
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Date: Wed, 15 Apr 2009 13:10:06 +0900 (JST)
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> * KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> [2009-04-15 11:04:59]:
> 
> >  	committed = atomic_long_read(&vm_committed_space);
> > +	if (committed < 0)
> > +		committed = 0;
> 
> Isn't this like pushing the problem under the rug?

global_page_state() already has same logic.
IOW almost meminfo filed has this one (except Commited_AS).


> >  	allowed = ((totalram_pages - hugetlb_total_pages())
> >  		* sysctl_overcommit_ratio / 100) + total_swap_pages;
> > 
> > Index: b/mm/swap.c
> > ===================================================================
> > --- a/mm/swap.c
> > +++ b/mm/swap.c
> > @@ -519,7 +519,7 @@ EXPORT_SYMBOL(pagevec_lookup_tag);
> >   * We tolerate a little inaccuracy to avoid ping-ponging the counter between
> >   * CPUs
> >   */
> > -#define ACCT_THRESHOLD	max(16, NR_CPUS * 2)
> > +#define ACCT_THRESHOLD	max_t(long, 16, num_online_cpus() * 2)
> >
> 
> Hmm.. this is a one time expansion, free of CPU hotplug.
> 
> Should we use nr_cpu_ids or num_possible_cpus()?

#define num_online_cpus()       cpumask_weight(cpu_online_mask)
#define num_possible_cpus()     cpumask_weight(cpu_possible_mask)

num_possible_cpus() have the same calculation cost.
nr_cpu_ids isn't proper value.
it point to valid cpu-id range, no related number of online nor possible cpus.