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Subject[PATCH v2 1/6] 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.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Hellwig <hch@lst.de>
---
arch/arm64/include/asm/memory.h | 9 ---------
arch/arm64/mm/init.c | 8 --------
include/asm-generic/fixmap.h | 1 +
include/linux/mm_types.h | 5 +++++
4 files changed, 6 insertions(+), 17 deletions(-)

diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index b96442960aea..f0a5c9531e8b 100644
--- 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 787e27964ab9..6a0b5c5a61af 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -615,14 +615,6 @@ 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 827e4d3bbc7a..8cc7b09c1bc7 100644
--- 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 5ed8f6292a53..ec8c16d9396b 100644
--- 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 ilog2(roundup_pow_of_two(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)

--
2.19.0
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