mm: introduce common STRUCT_PAGE_MAX_SHIFT define

This define is used by arm64 to calculate the size of the vmemmap region. It is defined as the log2 of the upper bound on the size of a struct page. We move it into mm_types.h so it can be defined properly instead of set and checked with a build bug. This also allows us to use the same define for riscv. Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Logan Gunthorpe <[email protected]> Acked-by: Will Deacon <[email protected]> Acked-by: Andrew Morton <[email protected]> Acked-by: Ard Biesheuvel <[email protected]> Acked-by: Catalin Marinas <[email protected]> Cc: Arnd Bergmann <[email protected]> Cc: Christoph Hellwig <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
brucespang · Dec 14, 2018 · d1402fc · d1402fc
1 parent 5b52609
commit d1402fc
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Showing 4 changed files with 6 additions and 17 deletions.
diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
@@ -34,15 +34,6 @@
  */
 #define PCI_IO_SIZE		SZ_16M
 
-/*
- * Log2 of the upper bound of the size of a struct page. Used for sizing
- * the vmemmap region only, does not affect actual memory footprint.
- * We don't use sizeof(struct page) directly since taking its size here
- * requires its definition to be available at this point in the inclusion
- * chain, and it may not be a power of 2 in the first place.
- */
-#define STRUCT_PAGE_MAX_SHIFT	6
-
 /*
  * VMEMMAP_SIZE - allows the whole linear region to be covered by
  *                a struct page array

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
@@ -610,14 +610,6 @@ void __init mem_init(void)
 	BUILD_BUG_ON(TASK_SIZE_32			> TASK_SIZE_64);
 #endif
 
-#ifdef CONFIG_SPARSEMEM_VMEMMAP
-	/*
-	 * Make sure we chose the upper bound of sizeof(struct page)
-	 * correctly when sizing the VMEMMAP array.
-	 */
-	BUILD_BUG_ON(sizeof(struct page) > (1 << STRUCT_PAGE_MAX_SHIFT));
-#endif
-
 	if (PAGE_SIZE >= 16384 && get_num_physpages() <= 128) {
 		extern int sysctl_overcommit_memory;
 		/*

diff --git a/include/asm-generic/fixmap.h b/include/asm-generic/fixmap.h
@@ -16,6 +16,7 @@
 #define __ASM_GENERIC_FIXMAP_H
 
 #include <linux/bug.h>
+#include <linux/mm_types.h>
 
 #define __fix_to_virt(x)	(FIXADDR_TOP - ((x) << PAGE_SHIFT))
 #define __virt_to_fix(x)	((FIXADDR_TOP - ((x)&PAGE_MASK)) >> PAGE_SHIFT)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
@@ -206,6 +206,11 @@ struct page {
 #endif
 } _struct_page_alignment;
 
+/*
+ * Used for sizing the vmemmap region on some architectures
+ */
+#define STRUCT_PAGE_MAX_SHIFT	(order_base_2(sizeof(struct page)))
+
 #define PAGE_FRAG_CACHE_MAX_SIZE	__ALIGN_MASK(32768, ~PAGE_MASK)
 #define PAGE_FRAG_CACHE_MAX_ORDER	get_order(PAGE_FRAG_CACHE_MAX_SIZE)