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Message-ID: <50B5CD9C.6010007@cn.fujitsu.com>
Date: Wed, 28 Nov 2012 16:38:52 +0800
From: Wen Congyang <wency@...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, 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
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@...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().
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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