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

Oscar Salvador
2021-03-08T18:49:23Z

On Thu, Mar 04, 2021 at 10:42:59AM -0800, Dave Hansen wrote:
> 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?

AFAIK, the biggest we populate vmemmap pages with is 2MB, plus the fact
that as you pointed out, memory sections on x86_64 are 128M, which is
way smaller than what would require to allocate a 1GB for vmemmap pages.

Am I missing something?

--
Oscar Salvador
SUSE L3