On 08.03.21 19:48, Oscar Salvador wrote:
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?
Right now, it is dead code that you are removing.
Just like for 2MB vmemmap pages, we would proactively have populate 1G
pages when adding individual sections. You can easily waste a lot of memory.
Of course, one could also make a final pass over the tables to see where
it makes sense forming 1GB pages.
But then, we would need quite some logic when removing individual
sections (e.g., a 128 MB DIMM) - and I remember there are corner cases
where we might have to remove boot memory ...
Long story short, I don't think 1G vmemmap pages are really worth the
trouble.
--
Thanks,
David / dhildenb
