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Date: Mon, 18 Aug 2014 13:13:20 -0700
From: Peter Grehan <grehan@freebsd.org>
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To: alc@freebsd.org, Konstantin Belousov <kostikbel@gmail.com>
Subject: Re: superpages for UMA
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Cc: arch@freebsd.org, Gleb Smirnoff <glebius@freebsd.org>,
 "Alexander V. Chernikov" <melifaro@freebsd.org>,
 "Andrey V. Elsukov" <ae@freebsd.org>
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> Newer Intel CPUs have more entries, and AMD CPUs have long (since
> Barcelona) had more.  In particular, they allow 2 MB page mappings to be
> cached in a larger L2 TLB.  Nowadays, the trouble is with the 1 GB pages.
> A lot of CPUs still only support an 8 entry, 1 level TLB for 1 GB pages.

  There are new(ish) ones effectively without 1GB pages. From the 
"Software Optimization Guide for AMD Family 16h Processors"

"Smashing"
   ...
"when the Family 16h processor encounters a 1-Gbyte page size, it will 
smash translations of that 1-Gbyte region into 2-Mbyte TLB entries, each
of which translates a 2-Mbyte region of the 1-Gbyte page."

later,

Peter.