mm/swap: fix release_pages() when releasing devmap pages

release_pages() is an optimized version of a loop around put_page().
Unfortunately for devmap pages the logic is not entirely correct in
release_pages().  This is because device pages can be more than type
MEMORY_DEVICE_PUBLIC.  There are in fact 4 types, private, public, FS DAX,
and PCI P2PDMA.  Some of these have specific needs to "put" the page while
others do not.

This logic to handle any special needs is contained in
put_devmap_managed_page().  Therefore all devmap pages should be processed
by this function where we can contain the correct logic for a page put.

Handle all device type pages within release_pages() by calling
put_devmap_managed_page() on all devmap pages.  If
put_devmap_managed_page() returns true the page has been put and we
continue with the next page.  A false return of put_devmap_managed_page()
means the page did not require special processing and should fall to
"normal" processing.

This was found via code inspection while determining if release_pages()
and the new put_user_pages() could be interchangeable.[1]

[1] https://lkml.kernel.org/r/20190523172852.GA27175@iweiny-DESK2.sc.intel.com

Link: https://lkml.kernel.org/r/20190605214922.17684-1-ira.weiny@intel.com
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

diff --git a/mm/swap.c b/mm/swap.c
index 7ede3ed..607c482 100644 (file)
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -740,15 +740,20 @@ void release_pages(struct page **pages, int nr)
                if (is_huge_zero_page(page))
                        continue;
 
-               /* Device public page can not be huge page */
-               if (is_device_public_page(page)) {
+               if (is_zone_device_page(page)) {
                        if (locked_pgdat) {
                                spin_unlock_irqrestore(&locked_pgdat->lru_lock,
                                                       flags);
                                locked_pgdat = NULL;
                        }
-                       put_devmap_managed_page(page);
-                       continue;
+                       /*
+                        * ZONE_DEVICE pages that return 'false' from
+                        * put_devmap_managed_page() do not require special
+                        * processing, and instead, expect a call to
+                        * put_page_testzero().
+                        */
+                       if (put_devmap_managed_page(page))
+                               continue;
                }
 
                page = compound_head(page);