[PATCH 2/4] mem-hotplug: Skip LOCAL_NODE_DATA pages in memory offline procedure.

[Tang Chen]

In memory offline procedure, skip pages marked as LOCAL_NODE_DATA.
For now, this kind of pages are used to store local node pagetables.

The minimum unit of memory online/offline is a memory block. In a
block, the movable pages will be offlined as usual (unmapped and
isolated), and the pagetable pages will be skipped. After the iteration
of all page, the block will be set as offline, but the kernel can
still access the pagetable pages. This is user transparent.

Signed-off-by: Tang Chen <tangchen@xxxxxxxxxxxxxx>
---
 mm/page_alloc.c     |   18 ++++++++++++++++--
 mm/page_isolation.c |    6 ++++++
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 557b21b..73b8f0b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5701,11 +5701,18 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
 	pfn = page_to_pfn(page);
 	for (found = 0, iter = 0; iter < pageblock_nr_pages; iter++) {
 		unsigned long check = pfn + iter;
+		unsigned long magic;
 
 		if (!pfn_valid_within(check))
 			continue;
 
 		page = pfn_to_page(check);
+
+		/* Skip pages storing local node kernel data. */
+		magic = (unsigned long)page->lru.next;
+		if (magic == LOCAL_NODE_DATA)
+			continue;
+
 		/*
 		 * We can't use page_count without pin a page
 		 * because another CPU can free compound page.
@@ -6029,8 +6036,7 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
 	struct page *page;
 	struct zone *zone;
 	int order, i;
-	unsigned long pfn;
-	unsigned long flags;
+	unsigned long pfn, flags, magic;
 	/* find the first valid pfn */
 	for (pfn = start_pfn; pfn < end_pfn; pfn++)
 		if (pfn_valid(pfn))
@@ -6046,6 +6052,14 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
 			continue;
 		}
 		page = pfn_to_page(pfn);
+
+		/* Skip pages storing local node kernel data. */
+		magic = (unsigned long)page->lru.next;
+		if (magic == LOCAL_NODE_DATA) {
+			pfn++;
+			continue;
+		}
+
 		/*
 		 * The HWPoisoned page may be not in buddy system, and
 		 * page_count() is not 0.
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index 383bdbb..fb60a27 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -174,6 +174,7 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn,
 				  bool skip_hwpoisoned_pages)
 {
 	struct page *page;
+	unsigned long magic;
 
 	while (pfn < end_pfn) {
 		if (!pfn_valid_within(pfn)) {
@@ -181,6 +182,8 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn,
 			continue;
 		}
 		page = pfn_to_page(pfn);
+		magic = (unsigned long)page->lru.next;
+
 		if (PageBuddy(page)) {
 			/*
 			 * If race between isolatation and allocation happens,
@@ -208,6 +211,9 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn,
 			 */
 			pfn++;
 			continue;
+		} else if (magic == LOCAL_NODE_DATA) {
+			pfn++;
+			continue;
 		}
 		else
 			break;
-- 
1.7.1

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