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

["Xie, Huawei" <huawei.xie@intel.com>]

On 11/19/2015 11:54 AM, Wang, Zhihong wrote:
>
>> -----Original Message-----
>> From: Xie, Huawei
>> Sent: Wednesday, November 18, 2015 8:08 PM
>> To: Wang, Zhihong <zhihong.wang@intel.com>; Mcnamara, John
>> <john.mcnamara@intel.com>; dev@dpdk.org
>> Subject: Re: [dpdk-dev] [RFC PATCH 2/2] lib/librte_eal: Remove unnecessary
>> hugepage zero-filling
>>
>> On 11/18/2015 6:45 PM, Wang, Zhihong wrote:
>>>> -----Original Message-----
>>>> From: Mcnamara, John
>>>> Sent: Wednesday, November 18, 2015 6:40 PM
>>>> To: Wang, Zhihong <zhihong.wang@intel.com>; dev@dpdk.org
>>>> Subject: RE: [dpdk-dev] [RFC PATCH 2/2] lib/librte_eal: Remove
>>>> unnecessary hugepage zero-filling
>>>>
>>>>
>>>>
>>>>> -----Original Message-----
>>>>> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Zhihong Wang
>>>>> Sent: Wednesday, November 18, 2015 3:27 AM
>>>>> To: dev@dpdk.org
>>>>> Subject: [dpdk-dev] [RFC PATCH 2/2] lib/librte_eal: Remove
>>>>> unnecessary hugepage zero-filling
>>>>>
>>>>> 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.
> I understand the concern.
> In my opinion application shouldn't assume malloced memory to be zero-filled. So it should be okay for DPDK even if the kernel doesn't zero the page at all.
For malloc, we shouldn't make this assumption because it might allocate
just freed memory from the heap. Hugetlbfs is different. Let us listen
to other people's opinion.
It will make life much easier if we could make this assumption.
>
> I agree that we should check if any code accidentally make that assumption. Currently there's rte_pktmbuf_init() for packet mbuf initialization.
>
> /Zhihong
>
>
>> 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 (orig) {
>>>>>  			hugepg_tbl[i].orig_va = virtaddr;
>>>>> -			memset(virtaddr, 0, hugepage_sz);
>>>>> +			memset(virtaddr, 0, 8);
>>>>>  		}
>>>> Probably worth adding a one or two line comment here to avoid someone
>>>> thinking that it is a bug at some later stage. The text in the commit
>>>> message above is suitable.
>>>>
>>> Good suggestion! Will add it :)
>>>
>>>> John.
>>>> --
>