mm: simplify freeing of devmap managed pages

Make put_devmap_managed_page return if it took charge of the page
or not and remove the separate page_is_devmap_managed helper.

Link: https://lkml.kernel.org/r/20220210072828.2930359-6-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Tested-by: "Sierra Guiza, Alejandro (Alex)" <alex.sierra@amd.com>

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Christian Knig <christian.koenig@amd.com>
Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Cc: Karol Herbst <kherbst@redhat.com>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: "Pan, Xinhui" <Xinhui.Pan@amd.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

include/linux/mm.h

@@ -1094,33 +1094,24 @@ static inline bool is_zone_movable_page(const struct page *page)
 #ifdef CONFIG_DEV_PAGEMAP_OPS
 DECLARE_STATIC_KEY_FALSE(devmap_managed_key);
 
-static inline bool page_is_devmap_managed(struct page *page)
+bool __put_devmap_managed_page(struct page *page);
+static inline bool put_devmap_managed_page(struct page *page)
 {
 	if (!static_branch_unlikely(&devmap_managed_key))
 		return false;
 	if (!is_zone_device_page(page))
 		return false;
-	switch (page->pgmap->type) {
+	if (page->pgmap->type != MEMORY_DEVICE_PRIVATE &&
-	case MEMORY_DEVICE_PRIVATE:
+	    page->pgmap->type != MEMORY_DEVICE_FS_DAX)
-	case MEMORY_DEVICE_FS_DAX:
-		return true;
-	default:
-		break;
-	}
 		return false;
+	return __put_devmap_managed_page(page);
 }
 
-void put_devmap_managed_page(struct page *page);
-
 #else /* CONFIG_DEV_PAGEMAP_OPS */
-static inline bool page_is_devmap_managed(struct page *page)
+static inline bool put_devmap_managed_page(struct page *page)
 {
 	return false;
 }
-
-static inline void put_devmap_managed_page(struct page *page)
-{
-}
 #endif /* CONFIG_DEV_PAGEMAP_OPS */
 
 static inline bool is_device_private_page(const struct page *page)
@@ -1220,16 +1211,11 @@ static inline void put_page(struct page *page)
 	struct folio *folio = page_folio(page);
 
 	/*
-	 * For devmap managed pages we need to catch refcount transition from
+	 * For some devmap managed pages we need to catch refcount transition
-	 * 2 to 1, when refcount reach one it means the page is free and we
+	 * from 2 to 1:
-	 * need to inform the device driver through callback. See
-	 * include/linux/memremap.h and HMM for details.
 	 */
-	if (page_is_devmap_managed(&folio->page)) {
+	if (put_devmap_managed_page(&folio->page))
-		put_devmap_managed_page(&folio->page);
 		return;
-	}
-
 	folio_put(folio);
 }
 

mm/memremap.c

@@ -502,24 +502,22 @@ void free_devmap_managed_page(struct page *page)
 	page->pgmap->ops->page_free(page);
 }
 
-void put_devmap_managed_page(struct page *page)
+bool __put_devmap_managed_page(struct page *page)
 {
-	int count;
-
-	if (WARN_ON_ONCE(!page_is_devmap_managed(page)))
-		return;
-
-	count = page_ref_dec_return(page);
-
 	/*
 	 * devmap page refcounts are 1-based, rather than 0-based: if
 	 * refcount is 1, then the page is free and the refcount is
 	 * stable because nobody holds a reference on the page.
 	 */
-	if (count == 1)
+	switch (page_ref_dec_return(page)) {
+	case 1:
 		free_devmap_managed_page(page);
-	else if (!count)
+		break;
+	case 0:
 		__put_page(page);
+		break;
+	}
+	return true;
 }
-EXPORT_SYMBOL(put_devmap_managed_page);
+EXPORT_SYMBOL(__put_devmap_managed_page);
 #endif /* CONFIG_DEV_PAGEMAP_OPS */

mm/swap.c

@@ -930,16 +930,8 @@ void release_pages(struct page **pages, int nr)
 				unlock_page_lruvec_irqrestore(lruvec, flags);
 				lruvec = NULL;
 			}
-			/*
+			if (put_devmap_managed_page(page))
-			 * ZONE_DEVICE pages that return 'false' from
-			 * page_is_devmap_managed() do not require special
-			 * processing, and instead, expect a call to
-			 * put_page_testzero().
-			 */
-			if (page_is_devmap_managed(page)) {
-				put_devmap_managed_page(page);
 				continue;
-			}
 			if (put_page_testzero(page))
 				put_dev_pagemap(page->pgmap);
 			continue;