mm: remove the extra ZONE_DEVICE struct page refcount

ZONE_DEVICE struct pages have an extra reference count that complicates
the code for put_page() and several places in the kernel that need to
check the reference count to see that a page is not being used (gup,
compaction, migration, etc.). Clean up the code so the reference count
doesn't need to be treated specially for ZONE_DEVICE pages.

Note that this excludes the special idle page wakeup for fsdax pages,
which still happens at refcount 1.  This is a separate issue and will
be sorted out later.  Given that only fsdax pages require the
notifiacation when the refcount hits 1 now, the PAGEMAP_OPS Kconfig
symbol can go away and be replaced with a FS_DAX check for this hook
in the put_page fastpath.

Based on an earlier patch from Ralph Campbell <rcampbell@nvidia.com>.

Link: https://lkml.kernel.org/r/20220210072828.2930359-8-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: Felix Kuehling <Felix.Kuehling@amd.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: Chaitanya Kulkarni <kch@nvidia.com>
Cc: Christian Knig <christian.koenig@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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index cb8bee88e70c..0201d258c646 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1090,7 +1090,7 @@ static inline bool is_zone_movable_page(const struct page *page)
 	return page_zonenum(page) == ZONE_MOVABLE;
 }
 
-#ifdef CONFIG_DEV_PAGEMAP_OPS
+#if defined(CONFIG_ZONE_DEVICE) && defined(CONFIG_FS_DAX)
 DECLARE_STATIC_KEY_FALSE(devmap_managed_key);
 
 bool __put_devmap_managed_page(struct page *page);
@@ -1103,12 +1103,12 @@ static inline bool put_devmap_managed_page(struct page *page)
 	return __put_devmap_managed_page(page);
 }
 
-#else /* CONFIG_DEV_PAGEMAP_OPS */
+#else /* CONFIG_ZONE_DEVICE && CONFIG_FS_DAX */
 static inline bool put_devmap_managed_page(struct page *page)
 {
 	return false;
 }
-#endif /* CONFIG_DEV_PAGEMAP_OPS */
+#endif /* CONFIG_ZONE_DEVICE && CONFIG_FS_DAX */
 
 /* 127: arbitrary random number, small enough to assemble well */
 #define folio_ref_zero_or_close_to_overflow(folio) \