mm, fault-injection: declare should_fail_alloc_page()

The mm/ directory can almost fully be built with W=1, which would help
in local development.  One remaining issue is missing prototype for
should_fail_alloc_page().  Thus add it next to the should_failslab()
prototype.

Note the previous attempt by commit f717309 ("mm/page_alloc: make
should_fail_alloc_page() static") had to be reverted by commit
54aa386 as it caused an unresolved symbol error with
CONFIG_DEBUG_INFO_BTF=y

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Vlastimil Babka <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: David Hildenbrand <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: tehcaster

include/linux/fault-inject.h

@@ -64,6 +64,8 @@ static inline struct dentry *fault_create_debugfs_attr(const char *name,
 
 struct kmem_cache;
 
+bool should_fail_alloc_page(gfp_t gfp_mask, unsigned int order);
+
 int should_failslab(struct kmem_cache *s, gfp_t gfpflags);
 #ifdef CONFIG_FAILSLAB
 extern bool __should_failslab(struct kmem_cache *s, gfp_t gfpflags);