linux-kernel - Re: [PATCH v4 2/3] x86/vmemmap: Drop handling of 1GB vmemmap ranges

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Date:   Thu, 4 Mar 2021 10:42:59 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Oscar Salvador <osalvador@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     David Hildenbrand <david@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Michal Hocko <mhocko@...nel.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/3] x86/vmemmap: Drop handling of 1GB vmemmap ranges

On 3/1/21 12:32 AM, Oscar Salvador wrote:
> We never get to allocate 1GB pages when mapping the vmemmap range.
> Drop the dead code both for the aligned and unaligned cases and leave
> only the direct map handling.

Could you elaborate a bit on why 1GB pages are never used?  It is just
unlikely to have a 64GB contiguous area of memory that needs 1GB of
contiguous vmemmap?  Or, does the fact that sections are smaller than
64GB keeps this from happening?