Hello,
On Tuesday, June 14, 2011 8:30 PM Arnd Bergmann wrote:
On Tuesday 14 June 2011 18:58:35 Michal Nazarewicz wrote:
On Tue, 14 Jun 2011 18:03:00 +0200, Arnd Bergmann wrote:
For all I know, that is something that is only true for a few very special Samsung devices,
Maybe. I'm just answering your question. :)
Ah yes, I forgot that separate regions for different purposes could decrease fragmentation.
That is indeed a good point, but having a good allocator algorithm could also solve this. I don't know too much about these allocation algorithms, but there are probably multiple working approaches to this.
I would suggest going forward without having multiple regions:
Is having support for multiple regions a bad thing? Frankly, removing this support will change code from reading context passed as argument to code reading context from global variable. Nothing is gained; functionality is lost.
What is bad IMHO is making them the default, which forces the board code to care about memory management details. I would much prefer to have contiguous allocation parameters tuned automatically to just work on most boards before we add ways to do board-specific hacks.
I see your concerns, but I really wonder how to determine the properties of the global/default cma pool. You definitely don't want to give all available memory o CMA, because it will have negative impact on kernel operation (kernel really needs to allocate unmovable pages from time to time).
The only solution I see now is to provide Kconfig entry to determine the size of the global CMA pool, but this still have some issues, especially for multi-board kernels (each board probably will have different amount of RAM and different memory-consuming devices available). It looks that each board startup code still might need to tweak the size of CMA pool. I can add a kernel command line option for it, but such solution also will not solve all the cases (afair there was a discussion about kernel command line parameters for memory configuration and the conclusion was that it should be avoided).
Best regards