On Tue, 15 Dec 2009 12:46:32 +0200
"Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx> wrote:
> On Tue, Dec 15, 2009 at 3:58 AM, KAMEZAWA Hiroyuki
> <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> > On Sat, 12 Dec 2009 00:59:19 +0200
> > "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx> wrote:
> > If you use have to use spinlock here, this is a system-wide spinlock,
> > threshold as "100" is too small, I think.
>
> What is reasonable value for THRESHOLDS_EVENTS_THRESH for you?
>
> In most cases spinlock taken only for two checks. Is it significant time?
>
I tend to think about "bad case" when I see spinlock.
And...I'm not sure but, recently, there are many VM users.
spinlock can be a big pitfall in some enviroment if not para-virtualized.
(I'm sorry I misunderstand somehing and VM handle this well...)
> Unfortunately, I can't test it on a big box. I have only dual-core system.
> It's not enough to test scalability.
>
please leave it as 100 for now. But there is a chance to do simple optimization
for reducing the number of checks.
example)
static void mem_cgroup_threshold(struct mem_cgroup *memcg, bool swap)
{
/* For handle memory allocation in rush, check jiffies */
*/
smp_rmb();
if (memcg->last_checkpoint_jiffies == jiffies)
return; /* reset event to half value ..*/
memcg->last_checkpoint_jiffies = jiffies;
smp_wmb();
.....
I think this kind of check is necessary for handle "Rushing" memory allocation
in scalable way. Above one is just an example, 1 tick may be too long.
Other simple plan is
/* Allow only one thread to do scan the list at the same time. */
if (atomic_inc_not_zero(&memcg->threahold_scan_count) {
atomic_dec(&memcg->threshold_scan_count);
return;
}
...
atomic_dec(&memcg->threahold_scan_count)
Some easy logic (as above) for taking care of scalability and commenary for that
is enough at 1st stage. Then, if there seems to be a trouble/concern, someone
(me?) will do some work later.
Thanks,
-Kame
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