[dpdk-dev] [RFC PATCH 2/2] lib/librte_eal: Remove unnecessary hugepage zero-filling

[Xie, Huawei]

On 11/19/2015 10:16 AM, Wang, Zhihong wrote:
>
>> -----Original Message-----
>> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Stephen Hemminger
>> Sent: Thursday, November 19, 2015 3:09 AM
>> To: Richardson, Bruce <bruce.richardson at intel.com>
>> Cc: dev at dpdk.org
>> Subject: Re: [dpdk-dev] [RFC PATCH 2/2] lib/librte_eal: Remove unnecessary
>> hugepage zero-filling
>>
>> On Wed, 18 Nov 2015 16:13:32 +0000
>> "Richardson, Bruce" <bruce.richardson at intel.com> wrote:
>>
>>>
>>>> -----Original Message-----
>>>> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Stephen
>>>> Hemminger
>>>> Sent: Wednesday, November 18, 2015 4:00 PM
>>>> To: Xie, Huawei <huawei.xie at intel.com>
>>>> Cc: dev at dpdk.org
>>>> Subject: Re: [dpdk-dev] [RFC PATCH 2/2] lib/librte_eal: Remove
>>>> unnecessary hugepage zero-filling
>>>>
>>>> On Wed, 18 Nov 2015 12:07:54 +0000
>>>> "Xie, Huawei" <huawei.xie at intel.com> wrote:
>>>>
>>>>>>>> The kernel fills new allocated (huge) pages with zeros.
>>>>>>>> DPDK just has to touch the pages to trigger the allocation.
>>>>> I think we shouldn't reply on the assumption that kernel has
>>>>> zeroed the memory. Kernel zeroes the memory mostly to avoid
>>>>> information leakage.It could also achieve this by setting each bit to 1.
>>>>> What we indeed need to check is later DPDK initialization code
>>>>> doesn't assume the memory has been zeroed. Otherwise zero only
>>>>> that part of the memory. Does this makes sense?
>>>> If all new pages are zero, why does DPDK have to pre-touch the pages
>>>> at all?
>>> The pages won't actually be mapped into the processes address space until
>> accessed.
>>> /Bruce
>> Isn't that what mmap MAP_POPULATE flag (not currently used) will do.
> Yes, the MAP_POPULATE does literally the same thing.
> This flag is implemented since Linux 2.5.46 according to Linux man page, guess that's why DPDK fault the page tables manually in the first place. :)
>
> I think we can use this flag since it makes the code clearer.
The manual says MAP_POPULATE is only supported for private mappings
since Linux 2.6.23.
>
> /Zhihong
>
>