[PATCH][v2] powerpc/mm: using two zones for freescale 64 bit kernel

[Kumar Gala]

On Sep 20, 2012, at 8:36 AM, Kumar Gala wrote:

> 
> On Sep 20, 2012, at 5:14 AM, Xie Shaohui-B21989 wrote:
> 
>>>> On Thu, 2012-08-30 at 15:49 -0500, Kumar Gala wrote:
>>>>> On Aug 24, 2012, at 5:50 AM, Shaohui Xie wrote:
>>>>> 
>>>>>> PowerPC platform only supports ZONE_DMA zone for 64bit kernel, so
>>>>>> all the memory will be put into this zone. If the memory size is
>>>>>> greater than the device's DMA capability and device uses
>>>>>> dma_alloc_coherent to allocate memory, it will get an address
>>>>>> which is over the device's DMA addressing, the device will fail.
>>>>>> 
>>>>>> So we split the memory to two zones: zone ZONE_DMA32 &
>>>>>> ZONE_NORMAL, since we already allocate PCICSRBAR/PEXCSRBAR right
>>>>>> below the 4G boundary (if the lowest PCI address is above 4G), so
>>>>>> we constrain the DMA zone ZONE_DMA32 to 2GB, also, we clear flag
>>>>>> __GFP_DMA &
>>>>>> __GFP_DMA32 and set __GFP_DMA32 only if the device's dma_mask <
>>>>>> total memory size. By doing this, devices which cannot DMA all the
>>>>>> memory will be limited to ZONE_DMA32, but devices which can DMA
>>>>>> all
>>>> the memory will not be affected by this limitation.
>>>>>> 
>>>>>> Signed-off-by: Shaohui Xie <Shaohui.Xie at freescale.com>
>>>>>> Signed-off-by: Mingkai Hu <Mingkai.hu at freescale.com>
>>>>>> Signed-off-by: Chen Yuanquan <B41889 at freescale.com>
>>>>>> ---
>>>>>> changes for v2:
>>>>>> 1. use a config option for using two zones (ZONE_DMA32 &
>>>>>> ZONE_NORMAL) in freescale 64 bit kernel.
>>>>>> 
>>>> 
>>>> There must have been a misunderstanding. I think this should be a
>>>> runtime choice, possibly by the platform code. Any reason that can't be
>>> done ?
>>>> 
>>> [S.H] Do you mean this:
>>> 
>>> phys_addr_t platform_dma_size (maybe a default value should be used, then
>>> platform code will change it)
>>> 
>>> if (top_of_ram > platform_dma_size)
>>> 	max_zone_pfns[ZONE_DMA] = platform_dma_size >> PAGE_SHIFT; else
>>> 	max_zone_pfns[ZONE_DMA] = top_of_ram >> PAGE_SHIFT;
>>> 
>>> max_zone_pfns[ZONE_NORMAL] = top_of_ram >> PAGE_SHIFT;
>>> 
>>>> Also how does Intel do it ?
>>> [S.H] below are codes in Intel:
>>> 
>>> 403 void __init zone_sizes_init(void)
>>> 404 {
>>> 405         unsigned long max_zone_pfns[MAX_NR_ZONES];
>>> 406
>>> 407         memset(max_zone_pfns, 0, sizeof(max_zone_pfns));
>>> 408
>>> 409 #ifdef CONFIG_ZONE_DMA
>>> 410         max_zone_pfns[ZONE_DMA]         = MAX_DMA_PFN;
>>> 411 #endif
>>> 412 #ifdef CONFIG_ZONE_DMA32
>>> 413         max_zone_pfns[ZONE_DMA32]       = MAX_DMA32_PFN;
>>> 414 #endif
>>> 415         max_zone_pfns[ZONE_NORMAL]      = max_low_pfn;
>>> 416 #ifdef CONFIG_HIGHMEM
>>> 417         max_zone_pfns[ZONE_HIGHMEM]     = max_pfn;
>>> 418 #endif
>>> 419
>>> 
>>> For x86_64, there is no CONFIG_HIGHMEM, so there will be three zones:
>>> ZONE_DMA/ZONE_DMA32/ZONE_NORMAL.
>>> 
>> [S.H] Hello, Ben,
>> 
>> I have some questions, though I'm still expecting your comments.
>> PPC does not have ZONE_DMA32 by default, if we want to use it, we need to add "config ZONE_DMA32" in Kconfig first.
>> If setting multiple zones without ZONE_DMA, kmalloc in "include/linux/slab_def.h" will fail if it uses flag GFP_DMA.
>> For the runtime choice in 64-bit kernel, what exactly multiple zones should be used?
>> "ZONE_DMA & ZONE_NORMAL" or "ZONE_DMA & ZONE_DMA32 & ZONE_NORMAL"?
>> Then what the size should be set for them respectively?
>> 
>> Please comment, Thanks!
> 
> I think Ben is saying that Kconfig would enable ZONE_DMA32 for all PPC64, but make it runtime/per platform how we setup the zone's such that either ZONE_DMA32 is set to MAX_DMA32_PFN or it set to same value as ZONE_DMA.
> 
> However that's just a guess.

Ben,

Can you help clarify your thoughts here.

thanks

- k