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

[Sergio Gonzalez Monroy <sergio.gonzalez.monroy@intel.com>]

On 19/11/2015 06:32, Wang, Zhihong wrote:
>> -----Original Message-----
>> From: Xie, Huawei
>> Sent: Thursday, November 19, 2015 2:05 PM
>> To: Wang, Zhihong <zhihong.wang@intel.com>; Stephen Hemminger
>> <stephen@networkplumber.org>; Richardson, Bruce
>> <bruce.richardson@intel.com>
>> Cc: dev@dpdk.org
>> Subject: Re: [dpdk-dev] [RFC PATCH 2/2] lib/librte_eal: Remove unnecessary
>> hugepage zero-filling
>>
>> On 11/19/2015 10:16 AM, Wang, Zhihong wrote:
>>>> -----Original Message-----
>>>> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Stephen
>>>> Hemminger
>>>> Sent: Thursday, November 19, 2015 3:09 AM
>>>> To: Richardson, Bruce <bruce.richardson@intel.com>
>>>> Cc: dev@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@intel.com> wrote:
>>>>
>>>>>> -----Original Message-----
>>>>>> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Stephen
>>>>>> Hemminger
>>>>>> Sent: Wednesday, November 18, 2015 4:00 PM
>>>>>> To: Xie, Huawei <huawei.xie@intel.com>
>>>>>> Cc: dev@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@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.
> I've done check before and MAP_SHARED | MAP_POPULATE worked together correctly. Is there any implicit complication here?
>

None that I can see.

Sergio
>>> /Zhihong
>>>
>>>