+ mm-sparse-only-sub-section-aligned-range-would-be-populated.patch added to -mm tree

[akpm@linux-foundation.org]

The patch titled
     Subject: mm/sparse: only sub-section aligned range would be populated
has been added to the -mm tree.  Its filename is
     mm-sparse-only-sub-section-aligned-range-would-be-populated.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/mm-sparse-only-sub-section-aligned-range-would-be-populated.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/mm-sparse-only-sub-section-aligned-range-would-be-populated.patch

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------------------------------------------------------
From: Wei Yang <richard.weiyang@linux.alibaba.com>
Subject: mm/sparse: only sub-section aligned range would be populated

There are two code path which invoke __populate_section_memmap()

  * sparse_init_nid()
  * sparse_add_section()

For both case, we are sure the memory range is sub-section aligned.

  * we pass PAGES_PER_SECTION to sparse_init_nid()
  * we check range by check_pfn_span() before calling
    sparse_add_section()

Also, the counterpart of __populate_section_memmap(), we don't do such
calculation and check since the range is checked by check_pfn_span() in
__remove_pages().

Clear the calculation and check to keep it simple and comply with its
counterpart.

Link: http://lkml.kernel.org/r/20200703031828.14645-1-richard.weiyang@linux.alibaba.com
Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/sparse-vmemmap.c |   18 +++++-------------
 1 file changed, 5 insertions(+), 13 deletions(-)

--- a/mm/sparse-vmemmap.c~mm-sparse-only-sub-section-aligned-range-would-be-populated
+++ a/mm/sparse-vmemmap.c
@@ -247,20 +247,12 @@ int __meminit vmemmap_populate_basepages
 struct page * __meminit __populate_section_memmap(unsigned long pfn,
 		unsigned long nr_pages, int nid, struct vmem_altmap *altmap)
 {
-	unsigned long start;
-	unsigned long end;
+	unsigned long start = (unsigned long) pfn_to_page(pfn);
+	unsigned long end = start + nr_pages * sizeof(struct page);
 
-	/*
-	 * The minimum granularity of memmap extensions is
-	 * PAGES_PER_SUBSECTION as allocations are tracked in the
-	 * 'subsection_map' bitmap of the section.
-	 */
-	end = ALIGN(pfn + nr_pages, PAGES_PER_SUBSECTION);
-	pfn &= PAGE_SUBSECTION_MASK;
-	nr_pages = end - pfn;