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SubjectRe: meminfo Committed_AS underflows
* KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> [2009-04-15 13:10:06]:

> > * 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).
>

OK

>
> > > 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.
>

Since the value is just a basis for thresholds, num_online_cpus()
might work.

--
Balbir


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