[RFC][Patch v9 2/6] KVM: Enables the kernel to isolate guest free pages

[Nitesh Narayan Lal]

This patch enables the kernel to scan the per cpu array
which carries head pages from the buddy free list of order
FREE_PAGE_HINTING_MIN_ORDER (MAX_ORDER - 1) by
guest_free_page_hinting().
guest_free_page_hinting() scans the entire per cpu array by
acquiring a zone lock corresponding to the pages which are
being scanned. If the page is still free and present in the
buddy it tries to isolate the page and adds it to a
dynamically allocated array.

Once this scanning process is complete and if there are any
isolated pages added to the dynamically allocated array
guest_free_page_report() is invoked. However, before this the
per-cpu array index is reset so that it can continue capturing
the pages from buddy free list.

In this patch guest_free_page_report() simply releases the pages back
to the buddy by using __free_one_page()

Signed-off-by: Nitesh Narayan Lal <nitesh@xxxxxxxxxx>
---
 include/linux/page_hinting.h |   5 ++
 mm/page_alloc.c              |   2 +-
 virt/kvm/page_hinting.c      | 154 +++++++++++++++++++++++++++++++++++
 3 files changed, 160 insertions(+), 1 deletion(-)

diff --git a/include/linux/page_hinting.h b/include/linux/page_hinting.h
index 90254c582789..d554a2581826 100644
--- a/include/linux/page_hinting.h
+++ b/include/linux/page_hinting.h
@@ -13,3 +13,8 @@
 
 void guest_free_page_enqueue(struct page *page, int order);
 void guest_free_page_try_hinting(void);
+extern int __isolate_free_page(struct page *page, unsigned int order);
+extern void __free_one_page(struct page *page, unsigned long pfn,
+			    struct zone *zone, unsigned int order,
+			    int migratetype);
+void release_buddy_pages(void *obj_to_free, int entries);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 684d047f33ee..d38b7eea207b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -814,7 +814,7 @@ static inline int page_is_buddy(struct page *page, struct page *buddy,
  * -- nyc
  */
 
-static inline void __free_one_page(struct page *page,
+inline void __free_one_page(struct page *page,
 		unsigned long pfn,
 		struct zone *zone, unsigned int order,
 		int migratetype)
diff --git a/virt/kvm/page_hinting.c b/virt/kvm/page_hinting.c
index 48b4b5e796b0..9885b372b5a9 100644
--- a/virt/kvm/page_hinting.c
+++ b/virt/kvm/page_hinting.c
@@ -1,5 +1,9 @@
 #include <linux/mm.h>
 #include <linux/page_hinting.h>
+#include <linux/page_ref.h>
+#include <linux/kvm_host.h>
+#include <linux/kernel.h>
+#include <linux/sort.h>
 
 /*
  * struct guest_free_pages- holds array of guest freed PFN's along with an
@@ -16,6 +20,54 @@ struct guest_free_pages {
 
 DEFINE_PER_CPU(struct guest_free_pages, free_pages_obj);
 
+/*
+ * struct guest_isolated_pages- holds the buddy isolated pages which are
+ * supposed to be freed by the host.
+ * @pfn: page frame number for the isolated page.
+ * @order: order of the isolated page.
+ */
+struct guest_isolated_pages {
+	unsigned long pfn;
+	unsigned int order;
+};
+
+void release_buddy_pages(void *obj_to_free, int entries)
+{
+	int i = 0;
+	int mt = 0;
+	struct guest_isolated_pages *isolated_pages_obj = obj_to_free;
+
+	while (i < entries) {
+		struct page *page = pfn_to_page(isolated_pages_obj[i].pfn);
+
+		mt = get_pageblock_migratetype(page);
+		__free_one_page(page, page_to_pfn(page), page_zone(page),
+				isolated_pages_obj[i].order, mt);
+		i++;
+	}
+	kfree(isolated_pages_obj);
+}
+
+void guest_free_page_report(struct guest_isolated_pages *isolated_pages_obj,
+			    int entries)
+{
+	release_buddy_pages(isolated_pages_obj, entries);
+}
+
+static int sort_zonenum(const void *a1, const void *b1)
+{
+	const unsigned long *a = a1;
+	const unsigned long *b = b1;
+
+	if (page_zonenum(pfn_to_page(a[0])) > page_zonenum(pfn_to_page(b[0])))
+		return 1;
+
+	if (page_zonenum(pfn_to_page(a[0])) < page_zonenum(pfn_to_page(b[0])))
+		return -1;
+
+	return 0;
+}
+
 struct page *get_buddy_page(struct page *page)
 {
 	unsigned long pfn = page_to_pfn(page);
@@ -33,9 +85,111 @@ struct page *get_buddy_page(struct page *page)
 static void guest_free_page_hinting(void)
 {
 	struct guest_free_pages *hinting_obj = &get_cpu_var(free_pages_obj);
+	struct guest_isolated_pages *isolated_pages_obj;
+	int idx = 0, ret = 0;
+	struct zone *zone_cur, *zone_prev;
+	unsigned long flags = 0;
+	int hyp_idx = 0;
+	int free_pages_idx = hinting_obj->free_pages_idx;
+
+	isolated_pages_obj = kmalloc(MAX_FGPT_ENTRIES *
+			sizeof(struct guest_isolated_pages), GFP_KERNEL);
+	if (!isolated_pages_obj) {
+		hinting_obj->free_pages_idx = 0;
+		put_cpu_var(hinting_obj);
+		return;
+		/* return some logical error here*/
+	}
+
+	sort(hinting_obj->free_page_arr, free_pages_idx,
+	     sizeof(unsigned long), sort_zonenum, NULL);
+
+	while (idx < free_pages_idx) {
+		unsigned long pfn = hinting_obj->free_page_arr[idx];
+		unsigned long pfn_end = hinting_obj->free_page_arr[idx] +
+			(1 << FREE_PAGE_HINTING_MIN_ORDER) - 1;
+
+		zone_cur = page_zone(pfn_to_page(pfn));
+		if (idx == 0) {
+			zone_prev = zone_cur;
+			spin_lock_irqsave(&zone_cur->lock, flags);
+		} else if (zone_prev != zone_cur) {
+			spin_unlock_irqrestore(&zone_prev->lock, flags);
+			spin_lock_irqsave(&zone_cur->lock, flags);
+			zone_prev = zone_cur;
+		}
+
+		while (pfn <= pfn_end) {
+			struct page *page = pfn_to_page(pfn);
+			struct page *buddy_page = NULL;
+
+			if (PageCompound(page)) {
+				struct page *head_page = compound_head(page);
+				unsigned long head_pfn = page_to_pfn(head_page);
+				unsigned int alloc_pages =
+					1 << compound_order(head_page);
+
+				pfn = head_pfn + alloc_pages;
+				continue;
+			}
+
+			if (page_ref_count(page)) {
+				pfn++;
+				continue;
+			}
+
+			if (PageBuddy(page) && page_private(page) >=
+			    FREE_PAGE_HINTING_MIN_ORDER) {
+				int buddy_order = page_private(page);
+
+				ret = __isolate_free_page(page, buddy_order);
+				if (ret) {
+					isolated_pages_obj[hyp_idx].pfn = pfn;
+					isolated_pages_obj[hyp_idx].order =
+								buddy_order;
+					hyp_idx += 1;
+				}
+				pfn = pfn + (1 << buddy_order);
+				continue;
+			}
+
+			buddy_page = get_buddy_page(page);
+			if (buddy_page && page_private(buddy_page) >=
+			    FREE_PAGE_HINTING_MIN_ORDER) {
+				int buddy_order = page_private(buddy_page);
+
+				ret = __isolate_free_page(buddy_page,
+							  buddy_order);
+				if (ret) {
+					unsigned long buddy_pfn =
+						page_to_pfn(buddy_page);
+
+					isolated_pages_obj[hyp_idx].pfn =
+								buddy_pfn;
+					isolated_pages_obj[hyp_idx].order =
+								buddy_order;
+					hyp_idx += 1;
+				}
+				pfn = page_to_pfn(buddy_page) +
+					(1 << buddy_order);
+				continue;
+			}
+			pfn++;
+		}
+		hinting_obj->free_page_arr[idx] = 0;
+		idx++;
+		if (idx == free_pages_idx)
+			spin_unlock_irqrestore(&zone_cur->lock, flags);
+	}
 
 	hinting_obj->free_pages_idx = 0;
 	put_cpu_var(hinting_obj);
+
+	if (hyp_idx > 0)
+		guest_free_page_report(isolated_pages_obj, hyp_idx);
+	else
+		kfree(isolated_pages_obj);
+		/* return some logical error here*/
 }
 
 int if_exist(struct page *page)
-- 
2.17.2