Re: [PATCH v2 2/3] x86/vmemmap: Drop handling of 1GB vmemmap ranges

[David Hildenbrand]

On 03.02.21 15:10, Oscar Salvador wrote:
> On Wed, Feb 03, 2021 at 02:33:56PM +0100, David Hildenbrand wrote:
> > One problem I see with existing code / this change making more obvious is
> > that when trying to remove in other granularity than we added (e.g., unplug
> > a 128MB DIMM avaialble during boot), we remove the direct map of unrelated
> > DIMMs.
>
> So, let me see if I understand your concern.
>
> We have a range that was mapped with 1GB page, and we try to remove
> a 128MB chunk from it.
> Yes, in that case we would clear the pud, and that is bad, so we should
> keep the PAGE_ALIGNED checks.
>
> Now, let us assume that scenario.
> If you have a 1GB mapped range and you remove it in smaller chunks bit by bit
> (e.g: 128M), the direct mapping of that range will never be cleared unless

No, that's exactly what's happening. Good thing is that it barely ever 
happens, so I assume leaving behind some direct mapping / page tables is 
not that bad.

--
Thanks,

David / dhildenb