RE: [PATCH 1/5] freepgt: free_pgtables use vma list

[Luck, Tony]

>How it works is that it knows the extent in each direction
>where mappings do not exist.
>
>Once we know we have a clear span up to the next PMD_SIZE
>modulo (and PUD_SIZE and so on and so forth) we know we
>can liberate the page table chunks covered by such ranges.

Ok ... I see that now (I was mostly looking at free_pgtables()
and missed the conditional in the arglist that passes the
start of the next vma into free_pgd_range() as the ceiling
until we run out of vmas and pass in "ceiling".

But I'm still confused by all the math on addr/end at each
level.  Rounding up/down at each level should presumably be
based on the size of objects at the next level.  So the pgd
code should round using PUD_MASK, pud should use PMD_MASK etc.
Perhaps I missed some updates, but the version of the patch
that I have (and the simulator) is using PMD_MASK in the
pgd_free_range() function ... which is surely wrong.

-Tony
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