Date:	Wed, 28 Nov 2012 16:28:19 +0800
From:	Jiang Liu <jiang.liu@...wei.com>
To:	Wen Congyang <wency@...fujitsu.com>
CC:	Bob Liu <lliubbo@...il.com>, Tang Chen <tangchen@...fujitsu.com>,
	<hpa@...or.com>, <akpm@...ux-foundation.org>, <rob@...dley.net>,
	<isimatu.yasuaki@...fujitsu.com>, <laijs@...fujitsu.com>,
	<linfeng@...fujitsu.com>, <yinghai@...nel.org>,
	<kosaki.motohiro@...fujitsu.com>, <minchan.kim@...il.com>,
	<mgorman@...e.de>, <rientjes@...gle.com>, <rusty@...tcorp.com.au>,
	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	<linux-doc@...r.kernel.org>, <m.szyprowski@...sung.com>
Subject: Re: [PATCH v2 0/5] Add movablecore_map boot option

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@...fujitsu.com> wrote:
>>>> On 11/27/2012 08:09 PM, Bob Liu wrote:
>>>>>
>>>>> On Tue, Nov 27, 2012 at 4:29 PM, Tang Chen<tangchen@...fujitsu.com>
>>>>> 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@...rt_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().

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


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