On Thu 23-06-11 15:27:34, KAMEZAWA Hiroyuki wrote:
> On Wed, 22 Jun 2011 17:53:09 +0200
> Michal Hocko <mhocko@xxxxxxx> wrote:
>
> > On Thu 16-06-11 12:54:00, KAMEZAWA Hiroyuki wrote:
[...]
> > > @@ -1616,17 +1629,32 @@ mem_cgroup_select_victim(struct mem_cgro
> > > /*
> > > * Always updating the nodemask is not very good - even if we have an empty
> > > * list or the wrong list here, we can start from some node and traverse all
> > > - * nodes based on the zonelist. So update the list loosely once per 10 secs.
> > > + * nodes based on the zonelist.
> > > *
> > > + * The counter of mem->numascan_update is updated once per
> > > + * NUMASCAN_EVENTS_TARGET. We update the numa information when we see
> > > + * the number of event is larger than 3% of limit or 64MB pagein/pageout.
> > > */
> > > +#define NUMASCAN_UPDATE_RATIO (3)
> > > +#define NUMASCAN_UPDATE_THRESH (16384UL) /* 16k events of pagein/pageout */
> > > static void mem_cgroup_may_update_nodemask(struct mem_cgroup *mem)
> > > {
> > > int nid;
> > > -
> > > - if (time_after(mem->next_scan_node_update, jiffies))
> > > + unsigned long long limit;
> > > + /* if no limit, we never reach here */
> > > + limit = res_counter_read_u64(&mem->res, RES_LIMIT);
> > > + limit /= PAGE_SIZE;
> > > + /* 3% of limit */
> > > + limit = (limit * NUMASCAN_UPDATE_RATIO/100UL);
> > > + limit = min_t(unsigned long long, limit, NUMASCAN_UPDATE_THRESH);
> > > + /*
> > > + * If the number of pagein/out event is larger than 3% of limit or
> > > + * 64MB pagein/out, refresh numa information.
> > > + */
> > > + if (atomic_read(&mem->numascan_update) < limit ||
> > > + !mutex_trylock(&mem->numascan_mutex))
> > > return;
> >
> > I am not sure whether a mutex is not overkill here. What about using an
> > atomic operation instead?
> >
>
> I think mutex is informative than atomic counter for code readers.
> If influence of overhead is not big, I'd like to use mutex.
I do not have a strong opinion on that. mem_cgroup is not that
widespread structure to think about every single byte. On the other hand
atomic test&set would do the same thing. We are already using atomic
operations to manipulate numascan_update so doing it whole atomic based
sounds natural.
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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