Re: [PATCH v2 0/5] Add movablecore_map boot option

[Wen Congyang]

At 11/28/2012 04:28 PM, Jiang Liu Wrote:
> On 2012-11-28 16:29, Wen Congyang wrote:
>> At 11/28/2012 12:08 PM, Jiang Liu Wrote:
>>> On 2012-11-28 11:24, Bob Liu wrote:
>>>> On Tue, Nov 27, 2012 at 8:49 PM, Tang Chen <tangchen@xxxxxxxxxxxxxx> wrote:
>>>>> On 11/27/2012 08:09 PM, Bob Liu wrote:
>>>>>>
>>>>>> On Tue, Nov 27, 2012 at 4:29 PM, Tang Chen<tangchen@xxxxxxxxxxxxxx>
>>>>>> wrote:
>>>>>>>
>>>>>>> Hi Liu,
>>>>>>>
>>>>>>>
>>>>>>> This feature is used in memory hotplug.
>>>>>>>
>>>>>>> In order to implement a whole node hotplug, we need to make sure the
>>>>>>> node contains no kernel memory, because memory used by kernel could
>>>>>>> not be migrated. (Since the kernel memory is directly mapped,
>>>>>>> VA = PA + __PAGE_OFFSET. So the physical address could not be changed.)
>>>>>>>
>>>>>>> User could specify all the memory on a node to be movable, so that the
>>>>>>> node could be hot-removed.
>>>>>>>
>>>>>>
>>>>>> Thank you for your explanation. It's reasonable.
>>>>>>
>>>>>> But i think it's a bit duplicated with CMA, i'm not sure but maybe we
>>>>>> can combine it with CMA which already in mainline?
>>>>>>
>>>>> Hi Liu,
>>>>>
>>>>> Thanks for your advice. :)
>>>>>
>>>>> CMA is Contiguous Memory Allocator, right?  What I'm trying to do is
>>>>> controlling where is the start of ZONE_MOVABLE of each node. Could
>>>>> CMA do this job ?
>>>>
>>>> cma will not control the start of ZONE_MOVABLE of each node, but it
>>>> can declare a memory that always movable
>>>> and all non movable allocate request will not happen on that area.
>>>>
>>>> Currently cma use a boot parameter "cma=" to declare a memory size
>>>> that always movable.
>>>> I think it might fulfill your requirement if extending the boot
>>>> parameter with a start address.
>>>>
>>>> more info at http://lwn.net/Articles/468044/
>>>>>
>>>>> And also, after a short investigation, CMA seems need to base on
>>>>> memblock. But we need to limit memblock not to allocate memory on
>>>>> ZONE_MOVABLE. As a result, we need to know the ranges before memblock
>>>>> could be used. I'm afraid we still need an approach to get the ranges,
>>>>> such as a boot option, or from static ACPI tables such as SRAT/MPST.
>>>>>
>>>>
>>>> Yes, it's based on memblock and with boot option.
>>>> In setup_arch32()
>>>>     dma_contiguous_reserve(0);   => will declare a cma area using
>>>> memblock_reserve()
>>>>
>>>>> I'm don't know much about CMA for now. So if you have any better idea,
>>>>> please share with us, thanks. :)
>>>>
>>>> My idea is reuse cma like below patch(even not compiled) and boot with
>>>> "cma=size@start_address".
>>>> I don't know whether it can work and whether suitable for your
>>>> requirement, if not forgive me for this noises.
>>>>
>>>> diff --git a/drivers/base/dma-contiguous.c b/drivers/base/dma-contiguous.c
>>>> index 612afcc..564962a 100644
>>>> --- a/drivers/base/dma-contiguous.c
>>>> +++ b/drivers/base/dma-contiguous.c
>>>> @@ -59,11 +59,18 @@ struct cma *dma_contiguous_default_area;
>>>>   */
>>>>  static const unsigned long size_bytes = CMA_SIZE_MBYTES * SZ_1M;
>>>>  static long size_cmdline = -1;
>>>> +static long cma_start_cmdline = -1;
>>>>
>>>>  static int __init early_cma(char *p)
>>>>  {
>>>> +       char *oldp;
>>>>         pr_debug("%s(%s)\n", __func__, p);
>>>> +       oldp = p;
>>>>         size_cmdline = memparse(p, &p);
>>>> +
>>>> +       if (*p == '@')
>>>> +               cma_start_cmdline = memparse(p+1, &p);
>>>> +       printk("cma start:0x%x, size: 0x%x\n", size_cmdline, cma_start_cmdline);
>>>>         return 0;
>>>>  }
>>>>  early_param("cma", early_cma);
>>>> @@ -127,8 +134,10 @@ void __init dma_contiguous_reserve(phys_addr_t limit)
>>>>         if (selected_size) {
>>>>                 pr_debug("%s: reserving %ld MiB for global area\n", __func__,
>>>>                          selected_size / SZ_1M);
>>>> -
>>>> -               dma_declare_contiguous(NULL, selected_size, 0, limit);
>>>> +               if (cma_size_cmdline != -1)
>>>> +                       dma_declare_contiguous(NULL, selected_size,
>>>> cma_start_cmdline, limit);
>>>> +               else
>>>> +                       dma_declare_contiguous(NULL, selected_size, 0, limit);
>>>>         }
>>>>  };
>>> Seems a good idea to reserve memory by reusing CMA logic, though need more
>>> investigation here. One of CMA goal is to ensure pages in CMA are really
>>> movable, and this patchset tries to achieve the same goal at a first glance.
>>
>> Hmm, I don't like to reuse CMA. Because CMA is used for DMA. If we reuse it
>> for movable memory, I think movable zone is enough. And the start address is
>> not acceptable, because we want to specify the start address for each node.
>>
>> I think we can implement movablecore_map like that:
>> 1. parse the parameter
>> 2. reserve the memory after efi_reserve_boot_services()
> This sounds good, but the code to reserve memory for movable
> nodes will be similar to dma_declare_contiguous().

Yes, it may be very similar. I think we can move it into mm/page_alloc.c, and
both cma and movablecore_map can use this function.

Thanks
Wen Congyang

> 
>> 3. release the memory in mem_init
>>
>> What about this?
>>
>> Thanks
>> Wen Congyang
>>>
>>>  
>>>
>>>
>>>
>>
>>
>> .
>>
> 
> 
> 

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