linux-kernel - [PATCH] arm64: mm: update SECTION_SIZE

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Date:	Mon, 13 Jun 2016 20:31:59 +0800
From:	Jisheng Zhang <jszhang@...vell.com>
To:	<catalin.marinas@....com>, <will.deacon@....com>
CC:	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, Jisheng Zhang <jszhang@...vell.com>
Subject: [PATCH] arm64: mm: update SECTION_SIZE_BITS to 27 for 4k pagesize

On one of my platforms, linux is given 1152MB memory. With current
SECTION_SIZE_BITS 30, the reserved memmap is larger, it's a waste for
us. Inspired by disscusion[1], reducing the SECTION_SIZE_BITS to 27
which means 128M section size saves us about 14MB, a huge gain for
embeded memory constrained system.

[1]http://lkml.iu.edu/hypermail/linux/kernel/1604.1/03036.html

Signed-off-by: Jisheng Zhang <jszhang@...vell.com>
---
 arch/arm64/include/asm/sparsemem.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/arm64/include/asm/sparsemem.h b/arch/arm64/include/asm/sparsemem.h
index 74a9d30..41c10f7 100644
--- a/arch/arm64/include/asm/sparsemem.h
+++ b/arch/arm64/include/asm/sparsemem.h
@@ -18,7 +18,11 @@
 
 #ifdef CONFIG_SPARSEMEM
 #define MAX_PHYSMEM_BITS	48
+#ifdef CONFIG_ARM64_64K_PAGES
 #define SECTION_SIZE_BITS	30
+#else
+#define SECTION_SIZE_BITS	27
+#endif
 #endif
 
 #endif
-- 
2.8.1