Paul Menage wrote:
quoted text
> On Sun, Jun 15, 2008 at 6:32 PM, KOSAKI Motohiro
> <kosaki.motohiro@jp.fujitsu.com> wrote:
>> honestly, I used res_counter on early version.
>> but I got bad performance.
> 
> Bad performance on the charge/uncharge?
> 
> The only difference I can see is that res_counter uses
> spin_lock_irqsave()/spin_unlock_irqrestore(), and you're using plain
> spin_lock()/spin_unlock().
> 
> Is the overhead of a pushf/cli/popf really going to matter compared
> with the overhead of forking/exiting a task?
> 
> Or approaching this from the other side, does res_counter really need
> irq-safe locking, or is it just being cautious?

We really need irq-safe locking. We can end up uncharging from reclaim context
(called under zone->lru_lock and mem->zone->lru_lock - held with interrupts
disabled)

I am going to convert the spin lock to a reader writers lock, so that reads from
user space do not cause contention. I'll experiment and look at the overhead.

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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