On 18/02/2019 17:04, Mark Rutland wrote:

On Mon, Feb 18, 2019 at 03:30:38PM +0000, Steven Price wrote:

quoted

On 18/02/2019 15:06, Peter Zijlstra wrote:

quoted

On Mon, Feb 18, 2019 at 02:29:52PM +0000, Mark Rutland wrote:

quoted

I think that Peter means p?d_huge(x) should imply p?d_large(x), e.g.

#define pmd_large(x) \
	(pmd_sect(x) || pmd_huge(x) || pmd_trans_huge(x))

... which should work regardless of CONFIG_HUGETLB_PAGE.

Yep, that.

I'm not aware of a situation where pmd_huge(x) is true but pmd_sect(x)
isn't. Equally for pmd_huge(x) and pmd_trans_huge(x).

What am I missing?

Having dug for a bit, I think you're right in asserting that pmd_sect()
should cover those.

I had worried that wouldn't cater for contiguous pmd entries, but those
have to be contiguous section entries, so they get picked up.

That said, do we have any special handling for contiguous PTEs? We use
those in kernel mappings regardless of hugetlb support, and I didn't
spot a pte_large() helper.

There's no special handling for contiguous PTEs because the page walk
code doesn't care - each PTE is valid individually even if it is part of
a contiguous group. So the walker can descend all levels in this case.
pte_large() if it existed would therefore always return 0.

The pte_entry() callback obviously might go looking for the contiguous
bit so that it can annotate the output correctly but that's different
from a 'large' page. The code in arch/arm64/mm/dump.c simply looks for
the PTE_CONT bit being set to do this annotation.

Steve

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