[PATCH] mm/migrate_device: Try to handle swapcache pages.

[mpenttil@redhat.com]

From: Mika Penttilä <mpenttil@redhat.com>

Migrating file pages and swapcache pages into device memory is not supported.
The decision is done based on page_mapping(). For now, swapcache pages are not migrated.

Things can however be improved, for swapcache pages. Try to get rid of the swap cache,
and if successful, go ahead as with other anonymous pages.

As a detail, do not mess with shmem pages, as they handle swap internally.

Cc: Alistair Popple <apopple@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Mika Penttilä <mpenttil@redhat.com>
---
 mm/migrate_device.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/mm/migrate_device.c b/mm/migrate_device.c
index d30c9de60b0d..e8169c58c341 100644
--- a/mm/migrate_device.c
+++ b/mm/migrate_device.c
@@ -12,6 +12,7 @@
 #include <linux/mmu_notifier.h>
 #include <linux/oom.h>
 #include <linux/pagewalk.h>
+#include <linux/shmem_fs.h>
 #include <linux/rmap.h>
 #include <linux/swapops.h>
 #include <asm/tlbflush.h>
@@ -750,10 +751,17 @@ static void __migrate_device_pages(unsigned long *src_pfns,
 			/*
 			 * For now only support anonymous memory migrating to
 			 * device private or coherent memory.
+			 *
+			 * Try to get rid of swap cache if possible.
+			 * Leave shmem pages alone, they handle swap internally
+			 *
 			 */
 			if (mapping) {
-				src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
-				continue;
+				if (shmem_mapping(mapping) ||
+				    !folio_free_swap(page_folio(page))) {
+					src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
+					continue;
+				}
 			}
 		} else if (is_zone_device_page(newpage)) {
 			/*
-- 
2.17.1