Re: mm: introduce new field "managed_pages" to struct zone

[Simon Jeons <simon.jeons@gmail.com>]

On 03/05/2013 12:37 AM, Jiang Liu wrote:
> On 03/04/2013 07:57 AM, Simon Jeons wrote:
>> Hi Jiang,
>> On 03/03/2013 11:43 PM, Jiang Liu wrote:
>>> Hi Simon,
>>>      Bootmem allocator is used to managed DMA and Normal memory only, and it does not manage highmem pages because kernel
>>> can't directly access highmem pages.
>> Why you say so? Could you point out where you figure out bootmem allocator doesn't handle highmem pages? In my understanding, it doesn't distinguish low memory or high memory.
> Hi Simon,

Hi Jiang,

The comments of max_pfn_mapped is "highest direct mapped pfn over 4GB", 
so if both bootmem allocator and memblock just manage direct mapping pages?
BTW, could you show me where you can figure out traditional bootmem 
allocator manages directly mapping pages?

> 	According to my understanding, bootmem allocator does only manages lowmem pages.
> For traditional bootmem allocator in mm/bootmem.c, it could only manages directly mapped lowmem pages.
> For new bootmem allocator in mm/nobootmem.c, it depends on memblock to do the real work. Let's take
> x86 as an example:
> 1) following code set memblock.current_limit to max_low_pfn.
> arch/x86/kernel/setup.c:	memblock.current_limit = get_max_mapped();
> 2) the core of bootmem allocator in nobootmem.c is function __alloc_memory_core_early(),
> which has following code to avoid allocate highmem pages:
> static void * __init __alloc_memory_core_early(int nid, u64 size, u64 align,
>                                          u64 goal, u64 limit)
> {
>          void *ptr;
>          u64 addr;
>
>          if (limit > memblock.current_limit)
>                  limit = memblock.current_limit;
>
>          addr = memblock_find_in_range_node(goal, limit, size, align, nid);
>          if (!addr)
>                  return NULL;
> }
>
> I guess it's the same for other architectures. On the other hand, some other architectures
> may allocate highmem pages during boot by directly using memblock interfaces. For example,
> ppc use memblock interfaces to allocate highmem pages for giagant hugetlb pages.
>
> I'm working a patch set to fix those cases.
>
> Regards!
> Gerry
>
>
>>>      Regards!
>>>      Gerry
>>>
>>> On 02/28/2013 02:13 PM, Simon Jeons wrote:
>>>> Hi Jiang,
>>>>
>>>> https://patchwork.kernel.org/patch/1781291/
>>>>
>>>> You said that the bootmem allocator doesn't touch *highmem pages*, so highmem zones' managed_pages is set to the accurate value "spanned_pages - absent_pages" in function free_area_init_core() and won't be updated anymore. Why it doesn't touch *highmem pages*? Could you point out where you figure out this?
>>>>

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