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SubjectRe: [PATCH mmotm 2.5/4] memcg: disable irq at page cgroup lock (Re: [PATCH -mmotm 3/4] memcg: dirty pages accounting and limiting infrastructure)
On Thu, 11 Mar 2010 13:31:23 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

> On Wed, 10 Mar 2010 09:26:24 +0530, Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> > * nishimura@mxp.nes.nec.co.jp <nishimura@mxp.nes.nec.co.jp> [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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