[PATCH RFC 5/8] mm: only mark section offline when all pages are offline

[David Hildenbrand]

If any page is still online, the section should stay online.

Signed-off-by: David Hildenbrand <da...@redhat.com>
---
 mm/page_alloc.c |  2 +-
 mm/sparse.c     | 25 ++++++++++++++++++++++++-
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 2e5dcfdb0908..ae9023da2ca2 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8013,7 +8013,6 @@ __offline_isolated_pages(unsigned long start_pfn, 
unsigned long end_pfn)
                        break;
        if (pfn == end_pfn)
                return;
-       offline_mem_sections(pfn, end_pfn);
        zone = page_zone(pfn_to_page(pfn));
        spin_lock_irqsave(&zone->lock, flags);
        pfn = start_pfn;
@@ -8051,6 +8050,7 @@ __offline_isolated_pages(unsigned long start_pfn, 
unsigned long end_pfn)
                pfn += (1 << order);
        }
        spin_unlock_irqrestore(&zone->lock, flags);
+       offline_mem_sections(start_pfn, end_pfn);
 }
 #endif
 
diff --git a/mm/sparse.c b/mm/sparse.c
index 58cab483e81b..44978cb18fed 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -623,7 +623,27 @@ void online_mem_sections(unsigned long start_pfn, unsigned 
long end_pfn)
 }
 
 #ifdef CONFIG_MEMORY_HOTREMOVE
-/* Mark all memory sections within the pfn range as online */
+static bool all_pages_in_section_offline(unsigned long section_nr)
+{
+       unsigned long pfn = section_nr_to_pfn(section_nr);
+       struct page *page;
+       int i;
+
+       for (i = 0; i < PAGES_PER_SECTION; i++, pfn++) {
+               if (!pfn_valid(pfn))
+                       continue;
+
+               page = pfn_to_page(pfn);
+               if (!PageOffline(page))
+                       return false;
+       }
+       return true;
+}
+
+/*
+ * Mark all memory sections within the pfn range as offline (if all pages
+ * of a memory section are already offline)
+ */
 void offline_mem_sections(unsigned long start_pfn, unsigned long end_pfn)
 {
        unsigned long pfn;
@@ -639,6 +659,9 @@ void offline_mem_sections(unsigned long start_pfn, unsigned 
long end_pfn)
                if (WARN_ON(!valid_section_nr(section_nr)))
                        continue;
 
+               if (!all_pages_in_section_offline(section_nr))
+                       continue;
+
                ms = __nr_to_section(section_nr);
                ms->section_mem_map &= ~SECTION_IS_ONLINE;
        }
-- 
2.14.3