[PATCH 2/9] mm: alloc_contig_freed_pages() added

[Marek Szyprowski]

From: KAMEZAWA Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com>

This commit introduces alloc_contig_freed_pages() function
which allocates (ie. removes from buddy system) free pages
in range.  Caller has to guarantee that all pages in range
are in buddy system.

Along with this function, a free_contig_pages() function is
provided which frees all (or a subset of) pages allocated
with alloc_contig_free_pages().

Michal Nazarewicz has modified the function to make it easier
to allocate not MAX_ORDER_NR_PAGES aligned pages by making it
return pfn of one-past-the-last allocated page.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com>
Signed-off-by: Michal Nazarewicz <m.nazarewicz at samsung.com>
[m.nazarewicz: added checks if all allocated pages comes from the
same memory zone]
Signed-off-by: Michal Nazarewicz <mina86 at mina86.com>
Signed-off-by: Kyungmin Park <kyungmin.park at samsung.com>
[m.szyprowski: fixed wrong condition in VM_BUG_ON assert]
Signed-off-by: Marek Szyprowski <m.szyprowski at samsung.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
---
 include/linux/mmzone.h         |   16 +++++++++
 include/linux/page-isolation.h |    5 +++
 mm/page_alloc.c                |   67 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 88 insertions(+), 0 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index a2760bb..862a834 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1168,6 +1168,22 @@ static inline int memmap_valid_within(unsigned long pfn,
 }
 #endif /* CONFIG_ARCH_HAS_HOLES_MEMORYMODEL */
 
+#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
+/*
+ * Both PFNs must be from the same zone!  If this function returns
+ * true, pfn_to_page(pfn1) + (pfn2 - pfn1) == pfn_to_page(pfn2).
+ */
+static inline bool zone_pfn_same_memmap(unsigned long pfn1, unsigned long pfn2)
+{
+	return pfn_to_section_nr(pfn1) == pfn_to_section_nr(pfn2);
+}
+
+#else
+
+#define zone_pfn_same_memmap(pfn1, pfn2) (true)
+
+#endif
+
 #endif /* !__GENERATING_BOUNDS.H */
 #endif /* !__ASSEMBLY__ */
 #endif /* _LINUX_MMZONE_H */
diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
index 58cdbac..b9fc428 100644
--- a/include/linux/page-isolation.h
+++ b/include/linux/page-isolation.h
@@ -33,6 +33,11 @@ test_pages_isolated(unsigned long start_pfn, unsigned long end_pfn);
 extern int set_migratetype_isolate(struct page *page);
 extern void unset_migratetype_isolate(struct page *page);
 
+/* The below functions must be run on a range from a single zone. */
+extern unsigned long alloc_contig_freed_pages(unsigned long start,
+					      unsigned long end, gfp_t flag);
+extern void free_contig_pages(unsigned long pfn, unsigned nr_pages);
+
 /*
  * For migration.
  */
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index bf4399a..fbfb920 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5706,6 +5706,73 @@ out:
 	spin_unlock_irqrestore(&zone->lock, flags);
 }
 
+unsigned long alloc_contig_freed_pages(unsigned long start, unsigned long end,
+				       gfp_t flag)
+{
+	unsigned long pfn = start, count;
+	struct page *page;
+	struct zone *zone;
+	int order;
+
+	VM_BUG_ON(!pfn_valid(start));
+	page = pfn_to_page(start);
+	zone = page_zone(page);
+
+	spin_lock_irq(&zone->lock);
+
+	for (;;) {
+		VM_BUG_ON(page_count(page) || !PageBuddy(page) ||
+			  page_zone(page) != zone);
+
+		list_del(&page->lru);
+		order = page_order(page);
+		count = 1UL << order;
+		zone->free_area[order].nr_free--;
+		rmv_page_order(page);
+		__mod_zone_page_state(zone, NR_FREE_PAGES, -(long)count);
+
+		pfn += count;
+		if (pfn >= end)
+			break;
+		VM_BUG_ON(!pfn_valid(pfn));
+
+		if (zone_pfn_same_memmap(pfn - count, pfn))
+			page += count;
+		else
+			page = pfn_to_page(pfn);
+	}
+
+	spin_unlock_irq(&zone->lock);
+
+	/* After this, pages in the range can be freed one be one */
+	count = pfn - start;
+	pfn = start;
+	for (page = pfn_to_page(pfn); count; --count) {
+		prep_new_page(page, 0, flag);
+		++pfn;
+		if (likely(zone_pfn_same_memmap(pfn - 1, pfn)))
+			++page;
+		else
+			page = pfn_to_page(pfn);
+	}
+
+	return pfn;
+}
+
+void free_contig_pages(unsigned long pfn, unsigned nr_pages)
+{
+	struct page *page = pfn_to_page(pfn);
+
+	while (nr_pages--) {
+		__free_page(page);
+		++pfn;
+		if (likely(zone_pfn_same_memmap(pfn - 1, pfn)))
+			++page;
+		else
+			page = pfn_to_page(pfn);
+	}
+}
+
 #ifdef CONFIG_MEMORY_HOTREMOVE
 /*
  * All pages in the range must be isolated before calling this.
-- 
1.7.1.569.g6f426