[PATCH] arm: allow all architectures to change max zone order

[PATCH] arm: allow all architectures to change max zone order

[Lucas Stach]

Many multimedia applications on architectures without an
IOMMU need large physically contiguous buffers and so need
to adjust the max zone order of the page allocator.

There is zero reason to not allow this adjustment on arches
other than SHMOBILE.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
---
 arch/arm/Kconfig |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 49d993c..6ceace8 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1710,7 +1710,7 @@ config HW_PERF_EVENTS
 source "mm/Kconfig"
 
 config FORCE_MAX_ZONEORDER
-	int "Maximum zone order" if ARCH_SHMOBILE
+	int "Maximum zone order"
 	range 11 64 if ARCH_SHMOBILE
 	default "12" if SOC_AM33XX
 	default "9" if SA1111
-- 
1.7.10.4

[PATCH] arm: allow all architectures to change max zone order

[Lucas Stach]

Am Freitag, den 31.05.2013, 19:02 +0200 schrieb Lucas Stach:
> Many multimedia applications on architectures without an
> IOMMU need large physically contiguous buffers and so need
> to adjust the max zone order of the page allocator.
> 
> There is zero reason to not allow this adjustment on arches
> other than SHMOBILE.
> 
> Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
> ---
>  arch/arm/Kconfig |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 49d993c..6ceace8 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -1710,7 +1710,7 @@ config HW_PERF_EVENTS
>  source "mm/Kconfig"
>  
>  config FORCE_MAX_ZONEORDER
> -	int "Maximum zone order" if ARCH_SHMOBILE
> +	int "Maximum zone order"
>  	range 11 64 if ARCH_SHMOBILE
>  	default "12" if SOC_AM33XX
>  	default "9" if SA1111

Ping. This is really straight forward and low risk.
-- 
Pengutronix e.K.                           | Lucas Stach                 |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-5076 |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

[PATCH] arm: allow all architectures to change max zone order

[Russell King - ARM Linux]

On Mon, Jul 01, 2013 at 04:33:49PM +0200, Lucas Stach wrote:
> Am Freitag, den 31.05.2013, 19:02 +0200 schrieb Lucas Stach:
> > Many multimedia applications on architectures without an
> > IOMMU need large physically contiguous buffers and so need
> > to adjust the max zone order of the page allocator.
> > 
> > There is zero reason to not allow this adjustment on arches
> > other than SHMOBILE.
> > 
> > Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
> > ---
> >  arch/arm/Kconfig |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> > index 49d993c..6ceace8 100644
> > --- a/arch/arm/Kconfig
> > +++ b/arch/arm/Kconfig
> > @@ -1710,7 +1710,7 @@ config HW_PERF_EVENTS
> >  source "mm/Kconfig"
> >  
> >  config FORCE_MAX_ZONEORDER
> > -	int "Maximum zone order" if ARCH_SHMOBILE
> > +	int "Maximum zone order"
> >  	range 11 64 if ARCH_SHMOBILE
> >  	default "12" if SOC_AM33XX
> >  	default "9" if SA1111
> 
> Ping. This is really straight forward and low risk.

According to my greps, this is the only copy of this mail that appeared
on the mailing lists in 2013.  I've really not been happy with the
blatent assertion in this commit message, so I've been ignoring the
patch in the patch system because of that... until now.

First, let's look at the default, which is 11.  That corresponds with
2^10 pages, which gives a maximum allocation of 4MB.  While that's
rather limiting when you want to allocate a 1080p framebuffer (which
works out at slightly over 8MB), it seems that it's entirely possible
to allocate such framebuffers without resorting to fiddling with this
when CMA is being used.

Indeed, on iMX6 with imx-drm, I have a 1080p frame buffer provided by
the current CMA memory backed implementation there just fine with the
default value of this.  So, large physically contiguous buffers can
definitely be allocated today without problem - with CMA.

Not using CMA for large memory buffers would be a mistake.  Memory
suffers from fragmentation, which makes large memory allocations
suffer - I see even 16K allocations fail with 3.x kernels.  So what
hope has a 4MB (or larger) allocation got?

CMA avoids that by setting aside a special region which is only used
for data which can be moved into other memory areas when required,
thereby reducing the effects of memory fragmentation in this area.

So, far from "zero reason", there's a very real reason: memory
fragmentation leading to OOM situations.  Rather than fiddling with
this seemingly easy-to-fiddle-with constant, please use an appropriately
adjusted CMA for your multimedia applications instead of alloc_pages().

Thanks.

-- 
FTTC broadband for 0.8mile line: now at 9.7Mbps down 460kbps up... slowly
improving, and getting towards what was expected from it.

[PATCH] arm: allow all architectures to change max zone order

[Lucas Stach]

Am Dienstag, den 17.06.2014, 16:08 +0100 schrieb Russell King - ARM
Linux:
> On Mon, Jul 01, 2013 at 04:33:49PM +0200, Lucas Stach wrote:
> > Am Freitag, den 31.05.2013, 19:02 +0200 schrieb Lucas Stach:
> > > Many multimedia applications on architectures without an
> > > IOMMU need large physically contiguous buffers and so need
> > > to adjust the max zone order of the page allocator.
> > > 
> > > There is zero reason to not allow this adjustment on arches
> > > other than SHMOBILE.
> > > 
> > > Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
> > > ---
> > >  arch/arm/Kconfig |    2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> > > index 49d993c..6ceace8 100644
> > > --- a/arch/arm/Kconfig
> > > +++ b/arch/arm/Kconfig
> > > @@ -1710,7 +1710,7 @@ config HW_PERF_EVENTS
> > >  source "mm/Kconfig"
> > >  
> > >  config FORCE_MAX_ZONEORDER
> > > -	int "Maximum zone order" if ARCH_SHMOBILE
> > > +	int "Maximum zone order"
> > >  	range 11 64 if ARCH_SHMOBILE
> > >  	default "12" if SOC_AM33XX
> > >  	default "9" if SA1111
> > 
> > Ping. This is really straight forward and low risk.
> 
> According to my greps, this is the only copy of this mail that appeared
> on the mailing lists in 2013.  I've really not been happy with the
> blatent assertion in this commit message, so I've been ignoring the
> patch in the patch system because of that... until now.
> 
> First, let's look at the default, which is 11.  That corresponds with
> 2^10 pages, which gives a maximum allocation of 4MB.  While that's
> rather limiting when you want to allocate a 1080p framebuffer (which
> works out at slightly over 8MB), it seems that it's entirely possible
> to allocate such framebuffers without resorting to fiddling with this
> when CMA is being used.
> 
> Indeed, on iMX6 with imx-drm, I have a 1080p frame buffer provided by
> the current CMA memory backed implementation there just fine with the
> default value of this.  So, large physically contiguous buffers can
> definitely be allocated today without problem - with CMA.
> 
> Not using CMA for large memory buffers would be a mistake.  Memory
> suffers from fragmentation, which makes large memory allocations
> suffer - I see even 16K allocations fail with 3.x kernels.  So what
> hope has a 4MB (or larger) allocation got?
> 
> CMA avoids that by setting aside a special region which is only used
> for data which can be moved into other memory areas when required,
> thereby reducing the effects of memory fragmentation in this area.
> 
> So, far from "zero reason", there's a very real reason: memory
> fragmentation leading to OOM situations.  Rather than fiddling with
> this seemingly easy-to-fiddle-with constant, please use an appropriately
> adjusted CMA for your multimedia applications instead of alloc_pages().
> 
While we carried this patch around exactly for the reason that
allocating large buffers did not succeed even with CMA in place, it
seems this is no longer true on todays kernels.

So you are entirely correct in discarding this patch.

Regards,
Lucas
-- 
Pengutronix e.K.             | Lucas Stach                 |
Industrial Linux Solutions   | http://www.pengutronix.de/  |

[PATCH] arm: allow all architectures to change max zone order

[Lucas Stach]

Russell, can you please take a look at this? Nobody else seems to care
about this and we have to carry it around as without it imx-drm is
broken for FullHD displays with a 32bpp framebuffer.

Regards,
Lucas

Am Freitag, den 31.05.2013, 19:02 +0200 schrieb Lucas Stach:
> Many multimedia applications on architectures without an
> IOMMU need large physically contiguous buffers and so need
> to adjust the max zone order of the page allocator.
> 
> There is zero reason to not allow this adjustment on arches
> other than SHMOBILE.
> 
> Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
> ---
>  arch/arm/Kconfig |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 49d993c..6ceace8 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -1710,7 +1710,7 @@ config HW_PERF_EVENTS
>  source "mm/Kconfig"
>  
>  config FORCE_MAX_ZONEORDER
> -	int "Maximum zone order" if ARCH_SHMOBILE
> +	int "Maximum zone order"
>  	range 11 64 if ARCH_SHMOBILE
>  	default "12" if SOC_AM33XX
>  	default "9" if SA1111

-- 
Pengutronix e.K.                           | Lucas Stach                 |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-5076 |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

[PATCH] arm: allow all architectures to change max zone order

[Russell King - ARM Linux]

On Mon, Apr 14, 2014 at 05:06:02PM +0200, Lucas Stach wrote:
> Russell, can you please take a look at this? Nobody else seems to care
> about this and we have to carry it around as without it imx-drm is
> broken for FullHD displays with a 32bpp framebuffer.

I intentionally decided to ignore it because of the argumentative
description in it that implies that I'm stupid for not making this
available everywhere.  So, it can wait a bit longer.

-- 
FTTC broadband for 0.8mile line: now at 9.7Mbps down 460kbps up... slowly
improving, and getting towards what was expected from it.

[PATCH] arm: allow all architectures to change max zone order

[Lucas Stach]

Hi Russell,

Am Montag, den 14.04.2014, 20:35 +0100 schrieb Russell King - ARM Linux:
> On Mon, Apr 14, 2014 at 05:06:02PM +0200, Lucas Stach wrote:
> > Russell, can you please take a look at this? Nobody else seems to care
> > about this and we have to carry it around as without it imx-drm is
> > broken for FullHD displays with a 32bpp framebuffer.
> 
> I intentionally decided to ignore it because of the argumentative
> description in it that implies that I'm stupid for not making this
> available everywhere.  So, it can wait a bit longer.
> 

I'm sorry, it wasn't my intention to imply anything personal here. The
last sentence in the commit message was just meant to say that I could
not think of a reason to restrict this to SHMOBILE.

Can we please get this back on a technical level? If there is anything
technically wrong with this patch, I would really like to know.

Regards,
Lucas
-- 
Pengutronix e.K.                           | Lucas Stach                 |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-5076 |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |