Hi!

For architectures with CONFIG_ARCH_HAS_SET_ALIAS, pages can be unmapped
briefly on the directmap, even when CONFIG_DEBUG_PAGEALLOC is not configured.
So this changes kernel_map_pages and kernel_page_present to be defined when
CONFIG_ARCH_HAS_SET_ALIAS is defined as well. It also changes places
(page_alloc.c) where those functions are assumed to only be implemented when
CONFIG_DEBUG_PAGEALLOC is defined.

Which architectures are that?

Should this be merged to the patch where HAS_SET_ALIAS is introduced? We
don't want broken hibernation in between....

-#ifdef CONFIG_DEBUG_PAGEALLOC
 extern bool _debug_pagealloc_enabled;
-extern void __kernel_map_pages(struct page *page, int numpages, int enable);
 
 static inline bool debug_pagealloc_enabled(void)
 {
-	return _debug_pagealloc_enabled;
+	return IS_ENABLED(CONFIG_DEBUG_PAGEALLOC) && _debug_pagealloc_enabled;
 }

This will break build AFAICT. _debug_pagealloc_enabled variable does
not exist in !CONFIG_DEBUG_PAGEALLOC case.

									Pavel

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