xen: add helpers for caching grant mapping pages

Instead of having similar helpers in multiple backend drivers use
common helpers for caching pages allocated via gnttab_alloc_pages().

Make use of those helpers in blkback and scsiback.

Cc: <stable@vger.kernel.org> # 5.9
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovksy@oracle.com>
Signed-off-by: Juergen Gross <jgross@suse.com>

2 files changed, 83 insertions, 49 deletions

diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index 523dcdf39cc9..e2e42912f241 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -813,6 +813,78 @@ int gnttab_alloc_pages(int nr_pages, struct page **pages)
 }
 EXPORT_SYMBOL_GPL(gnttab_alloc_pages);
 
+void gnttab_page_cache_init(struct gnttab_page_cache *cache)
+{
+	spin_lock_init(&cache->lock);
+	INIT_LIST_HEAD(&cache->pages);
+	cache->num_pages = 0;
+}
+EXPORT_SYMBOL_GPL(gnttab_page_cache_init);
+
+int gnttab_page_cache_get(struct gnttab_page_cache *cache, struct page **page)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&cache->lock, flags);
+
+	if (list_empty(&cache->pages)) {
+		spin_unlock_irqrestore(&cache->lock, flags);
+		return gnttab_alloc_pages(1, page);
+	}
+
+	page[0] = list_first_entry(&cache->pages, struct page, lru);
+	list_del(&page[0]->lru);
+	cache->num_pages--;
+
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(gnttab_page_cache_get);
+
+void gnttab_page_cache_put(struct gnttab_page_cache *cache, struct page **page,
+			   unsigned int num)
+{
+	unsigned long flags;
+	unsigned int i;
+
+	spin_lock_irqsave(&cache->lock, flags);
+
+	for (i = 0; i < num; i++)
+		list_add(&page[i]->lru, &cache->pages);
+	cache->num_pages += num;
+
+	spin_unlock_irqrestore(&cache->lock, flags);
+}
+EXPORT_SYMBOL_GPL(gnttab_page_cache_put);
+
+void gnttab_page_cache_shrink(struct gnttab_page_cache *cache, unsigned int num)
+{
+	struct page *page[10];
+	unsigned int i = 0;
+	unsigned long flags;
+
+	spin_lock_irqsave(&cache->lock, flags);
+
+	while (cache->num_pages > num) {
+		page[i] = list_first_entry(&cache->pages, struct page, lru);
+		list_del(&page[i]->lru);
+		cache->num_pages--;
+		if (++i == ARRAY_SIZE(page)) {
+			spin_unlock_irqrestore(&cache->lock, flags);
+			gnttab_free_pages(i, page);
+			i = 0;
+			spin_lock_irqsave(&cache->lock, flags);
+		}
+	}
+
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	if (i != 0)
+		gnttab_free_pages(i, page);
+}
+EXPORT_SYMBOL_GPL(gnttab_page_cache_shrink);
+
 void gnttab_pages_clear_private(int nr_pages, struct page **pages)
 {
 	int i;
diff --git a/drivers/xen/xen-scsiback.c b/drivers/xen/xen-scsiback.c
index 4acc4e899600..862162dca33c 100644
--- a/drivers/xen/xen-scsiback.c
+++ b/drivers/xen/xen-scsiback.c
@@ -99,6 +99,8 @@ struct vscsibk_info {
 	struct list_head v2p_entry_lists;
 
 	wait_queue_head_t waiting_to_free;
+
+	struct gnttab_page_cache free_pages;
 };
 
 /* theoretical maximum of grants for one request */
@@ -188,10 +190,6 @@ module_param_named(max_buffer_pages, scsiback_max_buffer_pages, int, 0644);
 MODULE_PARM_DESC(max_buffer_pages,
 "Maximum number of free pages to keep in backend buffer");
 
-static DEFINE_SPINLOCK(free_pages_lock);
-static int free_pages_num;
-static LIST_HEAD(scsiback_free_pages);
-
 /* Global spinlock to protect scsiback TPG list */
 static DEFINE_MUTEX(scsiback_mutex);
 static LIST_HEAD(scsiback_list);
@@ -207,41 +205,6 @@ static void scsiback_put(struct vscsibk_info *info)
 		wake_up(&info->waiting_to_free);
 }
 
-static void put_free_pages(struct page **page, int num)
-{
-	unsigned long flags;
-	int i = free_pages_num + num, n = num;
-
-	if (num == 0)
-		return;
-	if (i > scsiback_max_buffer_pages) {
-		n = min(num, i - scsiback_max_buffer_pages);
-		gnttab_free_pages(n, page + num - n);
-		n = num - n;
-	}
-	spin_lock_irqsave(&free_pages_lock, flags);
-	for (i = 0; i < n; i++)
-		list_add(&page[i]->lru, &scsiback_free_pages);
-	free_pages_num += n;
-	spin_unlock_irqrestore(&free_pages_lock, flags);
-}
-
-static int get_free_page(struct page **page)
-{
-	unsigned long flags;
-
-	spin_lock_irqsave(&free_pages_lock, flags);
-	if (list_empty(&scsiback_free_pages)) {
-		spin_unlock_irqrestore(&free_pages_lock, flags);
-		return gnttab_alloc_pages(1, page);
-	}
-	page[0] = list_first_entry(&scsiback_free_pages, struct page, lru);
-	list_del(&page[0]->lru);
-	free_pages_num--;
-	spin_unlock_irqrestore(&free_pages_lock, flags);
-	return 0;
-}
-
 static unsigned long vaddr_page(struct page *page)
 {
 	unsigned long pfn = page_to_pfn(page);
@@ -302,7 +265,8 @@ static void scsiback_fast_flush_area(struct vscsibk_pend *req)
 		BUG_ON(err);
 	}
 
-	put_free_pages(req->pages, req->n_grants);
+	gnttab_page_cache_put(&req->info->free_pages, req->pages,
+			      req->n_grants);
 	req->n_grants = 0;
 }
 
@@ -445,8 +409,8 @@ static int scsiback_gnttab_data_map_list(struct vscsibk_pend *pending_req,
 	struct vscsibk_info *info = pending_req->info;
 
 	for (i = 0; i < cnt; i++) {
-		if (get_free_page(pg + mapcount)) {
-			put_free_pages(pg, mapcount);
+		if (gnttab_page_cache_get(&info->free_pages, pg + mapcount)) {
+			gnttab_page_cache_put(&info->free_pages, pg, mapcount);
 			pr_err("no grant page\n");
 			return -ENOMEM;
 		}
@@ -796,6 +760,8 @@ static int scsiback_do_cmd_fn(struct vscsibk_info *info,
 		cond_resched();
 	}
 
+	gnttab_page_cache_shrink(&info->free_pages, scsiback_max_buffer_pages);
+
 	RING_FINAL_CHECK_FOR_REQUESTS(&info->ring, more_to_do);
 	return more_to_do;
 }
@@ -1233,6 +1199,8 @@ static int scsiback_remove(struct xenbus_device *dev)
 
 	scsiback_release_translation_entry(info);
 
+	gnttab_page_cache_shrink(&info->free_pages, 0);
+
 	dev_set_drvdata(&dev->dev, NULL);
 
 	return 0;
@@ -1263,6 +1231,7 @@ static int scsiback_probe(struct xenbus_device *dev,
 	info->irq = 0;
 	INIT_LIST_HEAD(&info->v2p_entry_lists);
 	spin_lock_init(&info->v2p_lock);
+	gnttab_page_cache_init(&info->free_pages);
 
 	err = xenbus_printf(XBT_NIL, dev->nodename, "feature-sg-grant", "%u",
 			    SG_ALL);
@@ -1879,13 +1848,6 @@ out:
 
 static void __exit scsiback_exit(void)
 {
-	struct page *page;
-
-	while (free_pages_num) {
-		if (get_free_page(&page))
-			BUG();
-		gnttab_free_pages(1, &page);
-	}
 	target_unregister_template(&scsiback_ops);
 	xenbus_unregister_driver(&scsiback_driver);
 }