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,
> 	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.

highmem is just used for x86, correct? ppc doesn't have highmem I think.

>
> 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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