Re: [PATCH mmotm 2.5/4] memcg: disable irq at page cgroup lock (Re:[PATCH -mmotm 3/4] memcg: dirty pages accounting and limitinginfrastructure)

[KAMEZAWA Hiroyuki]

On Thu, 11 Mar 2010 13:31:23 +0900
Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx> wrote:

> On Wed, 10 Mar 2010 09:26:24 +0530, Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> wrote:
> > * nishimura@xxxxxxxxxxxxxxxxx <nishimura@xxxxxxxxxxxxxxxxx> [2010-03-10 10:43:09]:

> I made a patch(attached) using both local_irq_disable/enable and local_irq_save/restore.
> local_irq_save/restore is used only in mem_cgroup_update_file_mapped.
> 
> And I attached a histogram graph of 30 times kernel build in root cgroup for each.
> 
>   before_root: no irq operation(original)
>   after_root: local_irq_disable/enable for all
>   after2_root: local_irq_save/restore for all
>   after3_root: mixed version(attached)
> 
> hmm, there seems to be a tendency that before < after < after3 < after2 ?
> Should I replace save/restore version to mixed version ?
> 

IMHO, starting from after2_root version is the easist.
If there is a chance to call lock/unlock page_cgroup can be called in
interrupt context, we _have to_ disable IRQ, anyway.
And if we have to do this, I prefer migration_lock rather than this mixture.

BTW, how big your system is ? Balbir-san's concern is for bigger machines.
But I'm not sure this change is affecte by the size of machines.
I'm sorry I have no big machine, now.

I'll consider yet another fix for race in account migration if I can.

Thanks,
-Kame


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