[052/118] mm/page_alloc: skip non present sections on zone initialization

Commit Message

Andrew Morton Jan. 31, 2020, 6:13 a.m. UTC

From: "Kirill A. Shutemov" <[e-mail]>
Subject: mm/page_alloc: skip non present sections on zone initialization

memmap_init_zone() can be called on the ranges with holes during the boot.
It will skip any non-valid PFNs one-by-one.  It works fine as long as
holes are not too big.

But huge holes in the memory map causes a problem.  It takes over 20
seconds to walk 32TiB hole.  x86-64 with 5-level paging allows for much
larger holes in the memory map which would practically hang the system.

Deferred struct page init doesn't help here.  It only works on the present
ranges.

Skipping non-present sections would fix the issue.

Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Kirill A. Shutemov <[e-mail]>
Reviewed-by: Baoquan He <[e-mail]>
Acked-by: Michal Hocko <[e-mail]>
Cc: Dan Williams <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Cc: Mel Gorman <[e-mail]>
Cc: "Jin, Zhi" <[e-mail]>
Cc: David Hildenbrand <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Oscar Salvador <[e-mail]>
Cc: Pavel Tatashin <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/page_alloc.c |   28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

Patch

--- a/mm/page_alloc.c~mm-page_alloc-skip-non-present-sections-on-zone-initialization
+++ a/mm/page_alloc.c
@@ -5848,6 +5848,30 @@  overlap_memmap_init(unsigned long zone,
 	return false;
 }
 
+#ifdef CONFIG_SPARSEMEM
+/* Skip PFNs that belong to non-present sections */
+static inline __meminit unsigned long next_pfn(unsigned long pfn)
+{
+	unsigned long section_nr;
+
+	section_nr = pfn_to_section_nr(++pfn);
+	if (present_section_nr(section_nr))
+		return pfn;
+
+	while (++section_nr <= __highest_present_section_nr) {
+		if (present_section_nr(section_nr))
+			return section_nr_to_pfn(section_nr);
+	}
+
+	return -1;
+}
+#else
+static inline __meminit unsigned long next_pfn(unsigned long pfn)
+{
+	return pfn++;
+}
+#endif
+
 /*
  * Initially all pages are reserved - free ones are freed
  * up by memblock_free_all() once the early boot process is
@@ -5887,8 +5911,10 @@  void __meminit memmap_init_zone(unsigned
 		 * function.  They do not exist on hotplugged memory.
 		 */
 		if (context == MEMMAP_EARLY) {
-			if (!early_pfn_valid(pfn))
+			if (!early_pfn_valid(pfn)) {
+				pfn = next_pfn(pfn) - 1;
 				continue;
+			}
 			if (!early_pfn_in_nid(pfn, nid))
 				continue;
 			if (overlap_memmap_init(zone, &pfn))