mm: add pte_batch_hint() to reduce scanning in folio_pte_batch()

Some architectures (e.g.  arm64) can tell from looking at a pte, if some
follow-on ptes also map contiguous physical memory with the same pgprot. 
(for arm64, these are contpte mappings).

Take advantage of this knowledge to optimize folio_pte_batch() so that it
can skip these ptes when scanning to create a batch.  By default, if an
arch does not opt-in, folio_pte_batch() returns a compile-time 1, so the
changes are optimized out and the behaviour is as before.

arm64 will opt-in to providing this hint in the next patch, which will
greatly reduce the cost of ptep_get() when scanning a range of contptes.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ryan Roberts <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Tested-by: John Hubbard <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Andrey Ryabinin <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: Barry Song <[email protected]>
Cc: Borislav Petkov (AMD) <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: James Morse <[email protected]>
Cc: Kefeng Wang <[email protected]>
Cc: Marc Zyngier <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Yang Shi <[email protected]>
Cc: Zi Yan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions