From: "Xie, Huawei" <huawei.xie@intel.com>
To: "Gonzalez Monroy, Sergio" <sergio.gonzalez.monroy@intel.com>,
"Wang, Zhihong" <zhihong.wang@intel.com>,
"Mcnamara, John" <john.mcnamara@intel.com>,
"dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [RFC PATCH 2/2] lib/librte_eal: Remove unnecessary hugepage zero-filling
Date: Mon, 23 Nov 2015 03:46:31 +0000 [thread overview]
Message-ID: <C37D651A908B024F974696C65296B57B4B1A6CFF@SHSMSX101.ccr.corp.intel.com> (raw)
In-Reply-To: <564D930C.7060108@intel.com>
On 11/19/2015 5:15 PM, Gonzalez Monroy, Sergio wrote:
> On 18/11/2015 12:07, Xie, Huawei wrote:
>> 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. 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?
>
> Why cannot we rely on the kernel zeroing the memory ?
> If that behavior were to change, then we can zero out the memory
> ourselves.
It is undocumented kernel behavior. My opinion is if not a big burden,
zero out the needed memory ourselves, otherwise resort to this kernel
behavior.
>
> Bruce pointed out to me that the semantics have changed a bit since we
> introduced
> rte_memzone_free.
> Before that, all memzone reserve were zero out by default.
> Is there code relying on that? I'm not sure, but it still is good
> practice to do it.
>
> I submitted an RFC regarding this:
> http://dpdk.org/ml/archives/dev/2015-November/028416.html
>
> The idea would be to keep the available memory we are managing zeroed
> at all times.
>
> Sergio
>>>>> ...
>>>>> 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.
>>>> --
>
>
next prev parent reply other threads:[~2015-11-23 3:46 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-18 3:27 [dpdk-dev] [RFC PATCH 0/2] Reduce DPDK initialization time Zhihong Wang
2015-11-18 3:27 ` [dpdk-dev] [RFC PATCH 1/2] lib/librte_eal: Reduce timer " Zhihong Wang
2015-11-18 3:27 ` [dpdk-dev] [RFC PATCH 2/2] lib/librte_eal: Remove unnecessary hugepage zero-filling Zhihong Wang
2015-11-18 10:39 ` Mcnamara, John
2015-11-18 10:44 ` Wang, Zhihong
2015-11-18 12:07 ` Xie, Huawei
2015-11-18 16:00 ` Stephen Hemminger
2015-11-18 16:13 ` Richardson, Bruce
2015-11-18 19:09 ` Stephen Hemminger
2015-11-19 2:15 ` Wang, Zhihong
2015-11-19 6:04 ` Xie, Huawei
2015-11-19 6:32 ` Wang, Zhihong
2015-11-19 9:18 ` Sergio Gonzalez Monroy
2015-11-23 2:54 ` Xie, Huawei
2015-11-23 10:18 ` Bruce Richardson
2015-11-20 12:15 ` Bruce Richardson
2015-11-19 3:54 ` Wang, Zhihong
2015-11-19 6:09 ` Xie, Huawei
2015-11-19 9:14 ` Sergio Gonzalez Monroy
2015-11-23 3:46 ` Xie, Huawei [this message]
2015-11-23 4:07 ` Stephen Hemminger
2015-11-23 5:05 ` Xie, Huawei
2015-11-23 6:52 ` Stephen Hemminger
2015-11-25 18:24 ` Xie, Huawei
2015-12-24 8:34 ` [dpdk-dev] [RFC PATCH 0/2] Reduce DPDK initialization time Qiu, Michael
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