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From: Balbir Singh on 3 Aug 2010 00:10
* KAMEZAWA Hiroyuki <kamezawa.hiroyu(a)jp.fujitsu.com> [2010-08-02 19:20:06]:

> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu(a)jp.fujitsu.com>
>
> This patch replaces bit_spinlock with spinlock. In general,
> spinlock has good functinality than bit_spin_lock and we should use
> it if we have a room for it. In 64bit arch, we have extra 4bytes.
> Let's use it.
> expected effects:
> - use better codes.
> - ticket lock on x86-64
> - para-vitualization aware lock
> etc..
>
> Chagelog: 20090729
> - fixed page_cgroup_is_locked().
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu(a)jp.fujitsu.com>
> --

The additional space usage is a big concern, I think saving space
would be of highest priority. I understand the expected benefits, but
a spinlock_t per page_cgroup is quite expensive at the moment. If
anything I think it should be a config option under CONFIG_DEBUG or
something else to play with and see the side effects.

--
Three Cheers,
Balbir
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From: KAMEZAWA Hiroyuki on 3 Aug 2010 00:40
On Tue, 3 Aug 2010 09:36:45 +0530
Balbir Singh <balbir(a)linux.vnet.ibm.com> wrote:

> * KAMEZAWA Hiroyuki <kamezawa.hiroyu(a)jp.fujitsu.com> [2010-08-02 19:20:06]:
>
> > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu(a)jp.fujitsu.com>
> >
> > This patch replaces bit_spinlock with spinlock. In general,
> > spinlock has good functinality than bit_spin_lock and we should use
> > it if we have a room for it. In 64bit arch, we have extra 4bytes.
> > Let's use it.
> > expected effects:
> > - use better codes.
> > - ticket lock on x86-64
> > - para-vitualization aware lock
> > etc..
> >
> > Chagelog: 20090729
> > - fixed page_cgroup_is_locked().
> >
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu(a)jp.fujitsu.com>
> > --
>
> The additional space usage is a big concern, I think saving space
> would be of highest priority. I understand the expected benefits, but
> a spinlock_t per page_cgroup is quite expensive at the moment. If
> anything I think it should be a config option under CONFIG_DEBUG or
> something else to play with and see the side effects.
>

Hmm. As I already wrote, packing id to flags is not easy.
leave 4 bytes space _pad for a while and drop this patch ?

I don't like to add CONFIG_DEBUG in this core.

Thanks,
-Kame


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