[PATCH v5 3/5] mm: remove the special early-section handling from pfn_valid() and for_each_valid_pfn()

[Yuan Liu]

Make pfn_valid() return 0 for PFNs that fall into invalid subsections
in early sections. Make for_each_valid_pfn() skip PFNs that fall into
invalid subsections in early sections.

This change is in preparation for optimizing zone contiguity checks
based on pages_with_online_memmap.

Reviewed-by: Wei Yang <richard.weiyang@xxxxxxxxx>
Reviewed-by: Jason Zeng <jason.zeng@xxxxxxxxx>
Signed-off-by: Yuan Liu <yuan1.liu@xxxxxxxxx>
---
 include/linux/mmzone.h | 13 ++++++-------
 mm/sparse-vmemmap.c    |  4 ++--
 2 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 9adb2ad21da5..783084f8bbfe 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -2259,6 +2259,10 @@ void sparse_init_early_section(int nid, struct page *map, unsigned long pnum,
  * there is actual usable memory at that @pfn. The struct page may
  * represent a hole or an unusable page frame.
  *
+ * Note that this function returns 0 for PFNs that fall into
+ * invalid subsections as part of early sections, even though there would
+ * currently be a memmap allocated (that should not be touched).
+ *
  * Return: 1 for PFNs that have memory map entries and 0 otherwise
  */
 static inline int pfn_valid(unsigned long pfn)
@@ -2283,11 +2287,7 @@ static inline int pfn_valid(unsigned long pfn)
 		rcu_read_unlock_sched();
 		return 0;
 	}
-	/*
-	 * Traditionally early sections always returned pfn_valid() for
-	 * the entire section-sized span.
-	 */
-	ret = early_section(ms) || pfn_section_valid(ms, pfn);
+	ret = pfn_section_valid(ms, pfn);
 	rcu_read_unlock_sched();
 
 	return ret;
@@ -2303,8 +2303,7 @@ static inline unsigned long first_valid_pfn(unsigned long pfn, unsigned long end
 	while (nr <= __highest_present_section_nr && pfn < end_pfn) {
 		struct mem_section *ms = __pfn_to_section(pfn);
 
-		if (valid_section(ms) &&
-		    (early_section(ms) || pfn_section_first_valid(ms, &pfn))) {
+		if (valid_section(ms) && pfn_section_first_valid(ms, &pfn)) {
 			rcu_read_unlock_sched();
 			return pfn;
 		}
diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index 6eadb9d116e4..c6eefbb6013f 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -771,8 +771,8 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
 	}
 
 	/*
-	 * The memmap of early sections is always fully populated. See
-	 * section_activate() and pfn_valid() .
+	 * The memmap of early sections is currently always fully populated. See
+	 * section_activate().
 	 */
 	if (!section_is_early) {
 		memmap_pages_add(-1L * (DIV_ROUND_UP(nr_pages * sizeof(struct page), PAGE_SIZE)));
-- 
2.47.3