[RFC PATCH v2 10/16] mm,hwpoison: Rework soft offline for free pages

[Oscar Salvador]

When trying to soft-offline a free page, we need to first take it off
the buddy allocator.
Once we know is out of reach, we can safely flag it as poisoned.

take_page_off_buddy will be used to take a page meant to be poisoned
off the buddy allocator.
take_page_off_buddy calls break_down_buddy_pages, which splits a
higher-order page in case our page belongs to one.

Once the page is under our control, we call page_set_poison to set it
as poisoned and grab a refcount on it.

Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
---
 mm/memory-failure.c | 20 +++++++++++-----
 mm/page_alloc.c     | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 82 insertions(+), 6 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 37b230b8cfe7..1d986580522d 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -78,6 +78,15 @@ EXPORT_SYMBOL_GPL(hwpoison_filter_dev_minor);
 EXPORT_SYMBOL_GPL(hwpoison_filter_flags_mask);
 EXPORT_SYMBOL_GPL(hwpoison_filter_flags_value);
 
+extern bool take_page_off_buddy(struct page *page);
+
+static void page_handle_poison(struct page *page)
+{
+	SetPageHWPoison(page);
+	page_ref_inc(page);
+	num_poisoned_pages_inc();
+}
+
 static int hwpoison_filter_dev(struct page *p)
 {
 	struct address_space *mapping;
@@ -1830,14 +1839,13 @@ static int soft_offline_in_use_page(struct page *page)
 
 static int soft_offline_free_page(struct page *page)
 {
-	int rc = dissolve_free_huge_page(page);
+	int rc = -EBUSY;
 
-	if (!rc) {
-		if (set_hwpoison_free_buddy_page(page))
-			num_poisoned_pages_inc();
-		else
-			rc = -EBUSY;
+	if (!dissolve_free_huge_page(page) && take_page_off_buddy(page)) {
+		page_handle_poison(page);
+		rc = 0;
 	}
+
 	return rc;
 }
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index cd1dd0712624..255df0c76a40 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8632,6 +8632,74 @@ bool is_free_buddy_page(struct page *page)
 
 #ifdef CONFIG_MEMORY_FAILURE
 /*
+ * Break down a higher-order page in sub-pages, and keep our target out of
+ * buddy allocator.
+ */
+static void break_down_buddy_pages(struct zone *zone, struct page *page,
+				   struct page *target, int low, int high,
+				   struct free_area *area, int migratetype)
+{
+	unsigned long size = 1 << high;
+	struct page *current_buddy, *next_page;
+
+	while (high > low) {
+		area--;
+		high--;
+		size >>= 1;
+
+		if (target >= &page[size]) {
+			next_page = page + size;
+			current_buddy = page;
+		} else {
+			next_page = page;
+			current_buddy = page + size;
+		}
+
+		if (set_page_guard(zone, current_buddy, high, migratetype))
+			continue;
+
+		if (current_buddy != target) {
+			add_to_free_area(current_buddy, area, migratetype);
+			set_page_order(current_buddy, high);
+			page = next_page;
+		}
+	}
+}
+
+/*
+ * Take a page that will be marked as poisoned off the buddy allocator.
+ */
+bool take_page_off_buddy(struct page *page)
+ {
+	struct zone *zone = page_zone(page);
+	unsigned long pfn = page_to_pfn(page);
+	unsigned long flags;
+	unsigned int order;
+	bool ret = false;
+
+	spin_lock_irqsave(&zone->lock, flags);
+	for (order = 0; order < MAX_ORDER; order++) {
+		struct page *page_head = page - (pfn & ((1 << order) - 1));
+		int buddy_order = page_order(page_head);
+		struct free_area *area = &(zone->free_area[buddy_order]);
+
+		if (PageBuddy(page_head) && buddy_order >= order) {
+			unsigned long pfn_head = page_to_pfn(page_head);
+			int migratetype = get_pfnblock_migratetype(page_head,
+		                                                   pfn_head);
+
+			del_page_from_free_area(page_head, area);
+			break_down_buddy_pages(zone, page_head, page, 0,
+		                               buddy_order, area, migratetype);
+			ret = true;
+		        break;
+		 }
+	}
+	spin_unlock_irqrestore(&zone->lock, flags);
+	return ret;
+ }
+
+/*
  * Set PG_hwpoison flag if a given page is confirmed to be a free page.  This
  * test is performed under the zone lock to prevent a race against page
  * allocation.
-- 
2.12.3