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

[Bruce Richardson <bruce.richardson@intel.com>]

On Wed, Nov 18, 2015 at 11:09:06AM -0800, Stephen Hemminger wrote:
> 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.

Hadn't seen that flag before, but it does indeed look to do exactly what we
want.

/Bruce