On 20.04.21 14:57, Mike Rapoport wrote:
On Tue, Apr 20, 2021 at 11:22:53AM +0200, David Hildenbrand wrote:
On 20.04.21 11:09, Mike Rapoport wrote:
From: Mike Rapoport <rppt@xxxxxxxxxxxxx>
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@xxxxxxx>
Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
---
include/linux/mmzone.h | 11 +++++++++++
1 file changed, 11 insertions(+)
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;
I'd rephrase all "there is a valid memory map" to "there is a memory map"
and add "pfn_valid() does to indicate whether the memory map as actually
initialized -- see pfn_to_online_page()."
pfn_valid() means that we can do a pfn_to_page() and don't get a fault when
accessing the "struct page". It doesn't state anything about the content.
Well, I mean valid in the sense you can access the struct page :)
How about:
/**
* pfn_valid - check if there is a memory map entry for a PFN
* @pfn: the page frame number to check
*
* Check if there is a memory map entry aka struct page for the @pfn and it
* is safe to access that struct page; the struct page state may be
* uninitialized -- see pfn_to_online_page().
*
* 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.
*/
Sounds good to me -- thanks!
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
--
Thanks,
David / dhildenb
