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/20181107205433.3875-2-logang@deltatee.com
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index b964429..f0a5c95 100644 (file)
--- 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
index 9b432d9..0340e45 100644 (file)
--- 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
index 827e4d3..8cc7b09 100644 (file)
--- 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
index 5ed8f62..2c471a2 100644 (file)
--- 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)