mm: move get_dev_pagemap out of line

This is a pretty big function, which should be out of line in general,
and a no-op stub if CONFIG_ZONE_DEVICЕ is not set.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 34 insertions, 2 deletions

diff --git a/kernel/memremap.c b/kernel/memremap.c
index 64b12c806cc5..3df6cd4ffb40 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -314,7 +314,7 @@ static void devm_memremap_pages_release(struct device *dev, void *data)
 }
 
 /* assumes rcu_read_lock() held at entry */
-struct dev_pagemap *find_dev_pagemap(resource_size_t phys)
+static struct dev_pagemap *find_dev_pagemap(resource_size_t phys)
 {
 	struct page_map *page_map;
 
@@ -501,8 +501,40 @@ struct vmem_altmap *to_vmem_altmap(unsigned long memmap_start)
 
 	return pgmap ? pgmap->altmap : NULL;
 }
-#endif /* CONFIG_ZONE_DEVICE */
 
+/**
+ * get_dev_pagemap() - take a new live reference on the dev_pagemap for @pfn
+ * @pfn: page frame number to lookup page_map
+ * @pgmap: optional known pgmap that already has a reference
+ *
+ * @pgmap allows the overhead of a lookup to be bypassed when @pfn lands in the
+ * same mapping.
+ */
+struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
+		struct dev_pagemap *pgmap)
+{
+	const struct resource *res = pgmap ? pgmap->res : NULL;
+	resource_size_t phys = PFN_PHYS(pfn);
+
+	/*
+	 * In the cached case we're already holding a live reference so
+	 * we can simply do a blind increment
+	 */
+	if (res && phys >= res->start && phys <= res->end) {
+		percpu_ref_get(pgmap->ref);
+		return pgmap;
+	}
+
+	/* fall back to slow path lookup */
+	rcu_read_lock();
+	pgmap = find_dev_pagemap(phys);
+	if (pgmap && !percpu_ref_tryget_live(pgmap->ref))
+		pgmap = NULL;
+	rcu_read_unlock();
+
+	return pgmap;
+}
+#endif /* CONFIG_ZONE_DEVICE */
 
 #if IS_ENABLED(CONFIG_DEVICE_PRIVATE) ||  IS_ENABLED(CONFIG_DEVICE_PUBLIC)
 void put_zone_device_private_or_public_page(struct page *page)