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[v3,1/4] include/linux/mmzone.h: add documentation for pfn_valid()

Message ID 20210422061902.21614-2-rppt@kernel.org (mailing list archive)
State New, archived
Headers show
Series arm64: drop pfn_valid_within() and simplify pfn_valid() | expand

Commit Message

Mike Rapoport April 22, 2021, 6:18 a.m. UTC 
From: Mike Rapoport <rppt@linux.ibm.com>

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().

Suggested-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
 include/linux/mmzone.h | 11 +++++++++++
 1 file changed, 11 insertions(+)
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Patch

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 47946cec7584..961f0eeefb62 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1410,6 +1410,17 @@  static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn)
 #endif
 
 #ifndef CONFIG_HAVE_ARCH_PFN_VALID
+/**
+ * pfn_valid - check if there is a valid memory map entry for a PFN
+ * @pfn: the page frame number to check
+ *
+ * Check if there is a valid memory map entry aka struct page for the @pfn.
+ * Note, that availability of the memory map entry does not imply that
+ * there is actual usable memory at that @pfn. The struct page may
+ * represent a hole or an unusable page frame.
+ *
+ * Return: 1 for PFNs that have memory map entries and 0 otherwise
+ */
 static inline int pfn_valid(unsigned long pfn)
 {
 	struct mem_section *ms;