include/linux/mmzone.h: add documentation for pfn_valid()

Patch series "arm64: drop pfn_valid_within() and simplify pfn_valid()", v4.

These patches aim to remove CONFIG_HOLES_IN_ZONE and essentially hardwire
pfn_valid_within() to 1.

The idea is to mark NOMAP pages as reserved in the memory map and restore
the intended semantics of pfn_valid() to designate availability of struct
page for a pfn.

With this the core mm will be able to cope with the fact that it cannot
use NOMAP pages and the holes created by NOMAP ranges within MAX_ORDER
blocks will be treated correctly even without the need for
pfn_valid_within.

This patch (of 4):

Add comment describing the semantics of pfn_valid() that clarifies that
pfn_valid() only checks for availability of a memory map entry (i.e.
struct page) for a PFN rather than availability of usable memory backing
that PFN.

The most "generic" version of pfn_valid() used by the configurations with
SPARSEMEM enabled resides in include/linux/mmzone.h so this is the most
suitable place for documentation about semantics of pfn_valid().

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Mike Rapoport <[email protected]>
Suggested-by: Anshuman Khandual <[email protected]>
Reviewed-by: Anshuman Khandual <[email protected]>
Acked-by: Ard Biesheuvel <[email protected]>
Reviewed-by: Kefeng Wang <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Marc Zyngier <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Will Deacon <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions