[PATCH v15 3/7] mm: Add function __putback_isolated_page

[Alexander Duyck]

From: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>

There are cases where we would benefit from avoiding having to go through
the allocation and free cycle to return an isolated page.

Examples for this might include page poisoning in which we isolate a page
and then put it back in the free list without ever having actually
allocated it.

This will enable us to also avoid notifiers for the future free page
reporting which will need to avoid retriggering page reporting when
returning pages that have been reported on.

Signed-off-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
---
 mm/internal.h       |    1 +
 mm/page_alloc.c     |   24 ++++++++++++++++++++++++
 mm/page_isolation.c |    6 ++----
 3 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index 3cf20ab3ca01..e1c908d0bf83 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -157,6 +157,7 @@ static inline struct page *pageblock_pfn_to_page(unsigned long start_pfn,
 }
 
 extern int __isolate_free_page(struct page *page, unsigned int order);
+extern void __putback_isolated_page(struct page *page, unsigned int order);
 extern void memblock_free_pages(struct page *page, unsigned long pfn,
 					unsigned int order);
 extern void __free_pages_core(struct page *page, unsigned int order);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e0a7895300fb..500b242c6f7f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3228,6 +3228,30 @@ int __isolate_free_page(struct page *page, unsigned int order)
 	return 1UL << order;
 }
 
+/**
+ * __putback_isolated_page - Return a now-isolated page back where we got it
+ * @page: Page that was isolated
+ * @order: Order of the isolated page
+ *
+ * This function is meant to return a page pulled from the free lists via
+ * __isolate_free_page back to the free lists they were pulled from.
+ */
+void __putback_isolated_page(struct page *page, unsigned int order)
+{
+	struct zone *zone = page_zone(page);
+	unsigned long pfn;
+	unsigned int mt;
+
+	/* zone lock should be held when this function is called */
+	lockdep_assert_held(&zone->lock);
+
+	pfn = page_to_pfn(page);
+	mt = get_pfnblock_migratetype(page, pfn);
+
+	/* Return isolated page to tail of freelist. */
+	__free_one_page(page, pfn, zone, order, mt);
+}
+
 /*
  * Update NUMA hit/miss statistics
  *
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index 04ee1663cdbe..d93d2be0070f 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -134,13 +134,11 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
 		__mod_zone_freepage_state(zone, nr_pages, migratetype);
 	}
 	set_pageblock_migratetype(page, migratetype);
+	if (isolated_page)
+		__putback_isolated_page(page, order);
 	zone->nr_isolate_pageblock--;
 out:
 	spin_unlock_irqrestore(&zone->lock, flags);
-	if (isolated_page) {
-		post_alloc_hook(page, order, __GFP_MOVABLE);
-		__free_pages(page, order);
-	}
 }
 
 static inline struct page *