Russell,
On 07/01/2015 02:48 PM, Russell King - ARM Linux wrote:
On Wed, Jul 01, 2015 at 01:53:02PM -0400, Murali Karicheri wrote:
Currently for Keystone devices, user can't change the
value of CONFIG_FORCE_MAX_ZONEORDER option in defconfig.
Users require capability to tune the value of this option on a target
board. So this patch adds this capability
No they shouldn't. If we do permit this, it should not be unrestricted -
it's a power-of-2 of the page size, so specifying something like 32768 is
insane.
Thanks for your comments
This was present in out internal version of the kernel. Only thing I can
recall is that this patch was added to fix an isue in a DEBUG buid.
Memory allocation for a large data structures used by a driver during
probe (internal version) was failing as the data structure gets expanded
as a result of DEBUG option related variables. There is no hurry to add
this for now.
In any case, it's well known that the Linux MM system fragments memory,
and the higher order allocations will fail soon after boot - and the
larger the order, the greater chance of it failing.Ok
Agree
The only case that you want large allocations is for things like DMA, and
we have a separate allocator for that called CMA, which is able to grab
large chunks of memory, provided it's configured with a large enough zone.
Please check whether CMA can be used _before_ considering using this
option. If you need to increase the order, it should be justified, and
it should be done on a per SoC basis in a static way, not left to the
user to dream up some power-of-2 figure.
I will explore these options when we upstream the internal driver. For
now I will drop this patch.
Thanks
--
Murali Karicheri
Linux Kernel, Keystone
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