Re: [PATCH v3 1/5] memblock: Introduce allocation direction to memblock.

[chen tang <imtangchen@gmail.com>]

Hi Wu,

Thanks, and will update the comments and msg in the next version.  :)

2013/9/14 Jianguo Wu <wujianguo@huawei.com>:
> Hi Tang,
>
> On 2013/9/13 17:30, Tang Chen wrote:
>
>> The Linux kernel cannot migrate pages used by the kernel. As a result, kernel
>> pages cannot be hot-removed. So we cannot allocate hotpluggable memory for
>> the kernel.
>>
>> ACPI SRAT (System Resource Affinity Table) contains the memory hotplug info.
>> But before SRAT is parsed, memblock has already started to allocate memory
>> for the kernel. So we need to prevent memblock from doing this.
>>
>> In a memory hotplug system, any numa node the kernel resides in should
>> be unhotpluggable. And for a modern server, each node could have at least
>> 16GB memory. So memory around the kernel image is highly likely unhotpluggable.
>>
>> So the basic idea is: Allocate memory from the end of the kernel image and
>> to the higher memory. Since memory allocation before SRAT is parsed won't
>> be too much, it could highly likely be in the same node with kernel image.
>>
>> The current memblock can only allocate memory from high address to low.
>> So this patch introduces the allocation direct to memblock. It could be
>> used to tell memblock to allocate memory from high to low or from low
>> to high.
>>
>> Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
>> Reviewed-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
>> ---
>>  include/linux/memblock.h |   22 ++++++++++++++++++++++
>>  mm/memblock.c            |   13 +++++++++++++
>>  2 files changed, 35 insertions(+), 0 deletions(-)
>>
>> diff --git a/include/linux/memblock.h b/include/linux/memblock.h
>> index 31e95ac..a7d3436 100644
>> --- a/include/linux/memblock.h
>> +++ b/include/linux/memblock.h
>> @@ -19,6 +19,11 @@
>>
>>  #define INIT_MEMBLOCK_REGIONS        128
>>
>> +/* Allocation order. */
>
> s/order/direction/
>
>> +#define MEMBLOCK_DIRECTION_HIGH_TO_LOW       0
>> +#define MEMBLOCK_DIRECTION_LOW_TO_HIGH       1
>> +#define MEMBLOCK_DIRECTION_DEFAULT   MEMBLOCK_DIRECTION_HIGH_TO_LOW
>> +
>>  struct memblock_region {
>>       phys_addr_t base;
>>       phys_addr_t size;
>> @@ -35,6 +40,7 @@ struct memblock_type {
>>  };
>>
>>  struct memblock {
>> +     int current_direction;      /* allocate from higher or lower address */
>>       phys_addr_t current_limit;
>>       struct memblock_type memory;
>>       struct memblock_type reserved;
>> @@ -148,6 +154,12 @@ phys_addr_t memblock_alloc_try_nid(phys_addr_t size, phys_addr_t align, int nid)
>>
>>  phys_addr_t memblock_alloc(phys_addr_t size, phys_addr_t align);
>>
>> +static inline bool memblock_direction_bottom_up(void)
>> +{
>> +     return memblock.current_direction == MEMBLOCK_DIRECTION_LOW_TO_HIGH;
>> +}
>> +
>> +
>>  /* Flags for memblock_alloc_base() amd __memblock_alloc_base() */
>>  #define MEMBLOCK_ALLOC_ANYWHERE      (~(phys_addr_t)0)
>>  #define MEMBLOCK_ALLOC_ACCESSIBLE    0
>> @@ -175,6 +187,16 @@ static inline void memblock_dump_all(void)
>>  }
>>
>>  /**
>> + * memblock_set_current_direction - Set current allocation direction to allow
>> + *                                  allocating memory from higher to lower
>> + *                                  address or from lower to higher address
>> + *
>> + * @direction: In which order to allocate memory. Could be
>
> s/order/direction/
>
>> + *             MEMBLOCK_DIRECTION_{HIGH_TO_LOW|LOW_TO_HIGH}
>> + */
>> +void memblock_set_current_direction(int direction);
>> +
>> +/**
>>   * memblock_set_current_limit - Set the current allocation limit to allow
>>   *                         limiting allocations to what is currently
>>   *                         accessible during boot
>> diff --git a/mm/memblock.c b/mm/memblock.c
>> index 0ac412a..f24ca2e 100644
>> --- a/mm/memblock.c
>> +++ b/mm/memblock.c
>> @@ -32,6 +32,7 @@ struct memblock memblock __initdata_memblock = {
>>       .reserved.cnt           = 1,    /* empty dummy entry */
>>       .reserved.max           = INIT_MEMBLOCK_REGIONS,
>>
>> +     .current_direction      = MEMBLOCK_DIRECTION_DEFAULT,
>>       .current_limit          = MEMBLOCK_ALLOC_ANYWHERE,
>>  };
>>
>> @@ -995,6 +996,18 @@ void __init_memblock memblock_trim_memory(phys_addr_t align)
>>       }
>>  }
>>
>> +void __init_memblock memblock_set_current_direction(int direction)
>> +{
>> +     if (direction != MEMBLOCK_DIRECTION_HIGH_TO_LOW &&
>> +         direction != MEMBLOCK_DIRECTION_LOW_TO_HIGH) {
>> +             pr_warn("memblock: Failed to set allocation order. "
>> +                     "Invalid order type: %d\n", direction);
>
> s/order/direction/
>
>> +             return;
>> +     }
>> +
>> +     memblock.current_direction = direction;
>> +}
>> +
>>  void __init_memblock memblock_set_current_limit(phys_addr_t limit)
>>  {
>>       memblock.current_limit = limit;
>
>
>
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