mm: use vmem_altmap code without CONFIG_ZONE_DEVICE

vmem_altmap_free() and vmem_altmap_offset() could be utlized without
CONFIG_ZONE_DEVICE enabled. For example,
mm/memory_hotplug.c:__add_pages() relies on that. The altmap is no longer
restricted to ZONE_DEVICE handling, but instead depends on
CONFIG_SPARSEMEM_VMEMMAP.

When CONFIG_SPARSEMEM_VMEMMAP is disabled, these functions are defined as
inline stubs, ensuring compatibility with configurations that do not use
sparsemem vmemmap. Without it, lkp reported the following:

ld: arch/x86/mm/init_64.o: in function `remove_pagetable':
init_64.c:(.meminit.text+0xfc7): undefined reference to
`vmem_altmap_free'

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Sumanth Korikkar <[e-mail]>
Reported-by: kernel test robot <[e-mail]>
Closes: https://lore.kernel.org/oe-kbuild-all/[e-mail]/
Reviewed-by: Gerald Schaefer <[e-mail]>
Acked-by: David Hildenbrand <[e-mail]>
Cc: Alexander Gordeev <[e-mail]>
Cc: Aneesh Kumar K.V <[e-mail]>
Cc: Anshuman Khandual <[e-mail]>
Cc: Heiko Carstens <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Oscar Salvador <[e-mail]>
Cc: Vasily Gorbik <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

include/linux/memremap.h

···
 		struct dev_pagemap *pgmap);
 bool pgmap_pfn_valid(struct dev_pagemap *pgmap, unsigned long pfn);
 
-unsigned long vmem_altmap_offset(struct vmem_altmap *altmap);
-void vmem_altmap_free(struct vmem_altmap *altmap, unsigned long nr_pfns);
 unsigned long memremap_compat_align(void);
 #else
 static inline void *devm_memremap_pages(struct device *dev,
···
 static inline bool pgmap_pfn_valid(struct dev_pagemap *pgmap, unsigned long pfn)
 {
 	return false;
-}
-
-static inline unsigned long vmem_altmap_offset(struct vmem_altmap *altmap)
-{
-	return 0;
-}
-
-static inline void vmem_altmap_free(struct vmem_altmap *altmap,
-		unsigned long nr_pfns)
-{
 }
 
 /* when memremap_pages() is disabled all archs can remap a single page */

include/linux/mm.h

···
 		struct vmem_altmap *altmap);
 #endif
 
+#ifdef CONFIG_SPARSEMEM_VMEMMAP
+static inline unsigned long vmem_altmap_offset(struct vmem_altmap *altmap)
+{
+	/* number of pfns from base where pfn_to_page() is valid */
+	if (altmap)
+		return altmap->reserve + altmap->free;
+	return 0;
+}
+
+static inline void vmem_altmap_free(struct vmem_altmap *altmap,
+				    unsigned long nr_pfns)
+{
+	altmap->alloc -= nr_pfns;
+}
+#else
+static inline unsigned long vmem_altmap_offset(struct vmem_altmap *altmap)
+{
+	return 0;
+}
+
+static inline void vmem_altmap_free(struct vmem_altmap *altmap,
+				    unsigned long nr_pfns)
+{
+}
+#endif
+
 #define VMEMMAP_RESERVE_NR	2
 #ifdef CONFIG_ARCH_WANT_OPTIMIZE_DAX_VMEMMAP
 static inline bool __vmemmap_can_optimize(struct vmem_altmap *altmap,

mm/memremap.c

···
 #include <linux/memremap.h>
 #include <linux/pfn_t.h>
 #include <linux/swap.h>
+#include <linux/mm.h>
 #include <linux/mmzone.h>
 #include <linux/swapops.h>
 #include <linux/types.h>
···
 	devm_release_action(dev, devm_memremap_pages_release, pgmap);
 }
 EXPORT_SYMBOL_GPL(devm_memunmap_pages);
-
-unsigned long vmem_altmap_offset(struct vmem_altmap *altmap)
-{
-	/* number of pfns from base where pfn_to_page() is valid */
-	if (altmap)
-		return altmap->reserve + altmap->free;
-	return 0;
-}
-
-void vmem_altmap_free(struct vmem_altmap *altmap, unsigned long nr_pfns)
-{
-	altmap->alloc -= nr_pfns;
-}
 
 /**
  * get_dev_pagemap() - take a new live reference on the dev_pagemap for @pfn