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 at intel.com>; dev at 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 at dpdk.org] On Behalf Of Zhihong Wang >>>> Sent: Wednesday, November 18, 2015 3:27 AM >>>> To: dev at 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. 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. >>> --
