linux-kernel - Re: [PATCH v2 0/5] Add movablecore

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Message-ID: <50B87A56.7010902@cn.fujitsu.com>
Date:	Fri, 30 Nov 2012 17:20:22 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Jiang Liu <jiang.liu@...wei.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, wency@...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 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.
> 

The approach is already implemented: https://lkml.org/lkml/2012/7/4/145
(add new MIGRATE_HOTREMOVE, not reuse MIGRATE_CMA)

MIGRATE_HOTREMOVE and MIGRATE_CMA both have this problem:
https://lkml.org/lkml/2012/7/5/83

R.I.P for this idea.

zone->managed_pages(you proposed, but don't manage MIGRATE_HOTREMOVE nor MIGRATE_CMA) +
proxy zone(handle all MIGRATE_HOTREMOVE, MIGRATE_CMA and ZONE_MOVABLE of the node)
may be a good idea.

Thanks,
Lai
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