Re: [dpdk-dev] [RFC PATCH 4/5] EAL: Add new EAL "--shm" option.

["Tan, Jianfeng" <jianfeng.tan@intel.com>]

Hi Tetsuya,

On 1/22/2016 9:43 AM, Tan, Jianfeng wrote:
> Hi Tetsuya,
>
> On 1/21/2016 7:07 PM, Tetsuya Mukawa wrote:
>> This is a temporary patch to get EAL memory under 16T(1 << 44).
>>
>> The patch adds new EAL "--shm" option. If the option is specified,
>> EAL will allocate one file from hugetlbfs. This memory is for sharing
>> memory between DPDK applicaiton and QEMU ivhsmem device.
>>
>> Signed-off-by: Tetsuya Mukawa <mukawa@igel.co.jp>
>> ---
>>   lib/librte_eal/common/eal_common_options.c |  5 ++
>>   lib/librte_eal/common/eal_internal_cfg.h   |  1 +
>>   lib/librte_eal/common/eal_options.h        |  2 +
>>   lib/librte_eal/common/include/rte_memory.h |  5 ++
>>   lib/librte_eal/linuxapp/eal/eal_memory.c   | 76 
>> ++++++++++++++++++++++++++++++
>>   5 files changed, 89 insertions(+)
>>
>
...
>> +    vaddr = mmap((void *)(1ULL << 43), size, PROT_READ | PROT_WRITE,
>> +            MAP_SHARED | MAP_FIXED, fd, 0);
>> +    if (vaddr != MAP_FAILED) {
>> +        memset(vaddr, 0, size);
>> +        *pfd = fd;
>> +    }
>
> I'm not sure if hard-coded way is good enough. It's known that kernel 
> manages VMAs using red-black tree, but I don't know if kernel 
> allocates VMA from low address to high address (if yes, can we 
> leverage this feature?).
>

A little more:it seems that kernel uses arch_get_unmapped_area_topdown() 
-> unmapped_area_topdown() to do that, which starts at 
mm->highest_vm_end. If this value bigger than (1ULL << 44)?

Thanks,
Jianfeng