Re: [RFC][PATCH 3/9] actual generic PAGE_SIZE infrastructure

Dave Hansen
2006-08-31T20:50:41Z

Here's the latest version I have, with much improved help text, thanks
to Christoph Lameter.

-----

* Add _ALIGN_UP() which we'll use now and _ALIGN_DOWN(), just for
parity.
* Define ASM_CONST() macro to help using constants in both assembly
and C code. Several architectures have some form of this, and
they will be consolidated around this one.
* Actually create PAGE_SHIFT and PAGE_SIZE macros
* For now, require that architectures enable GENERIC_PAGE_SIZE in
order to get this new code. This option will be removed by the
last patch in the series, and makes the series bisect-safe.
* Note that this moves the compiler.h define outside of the
#ifdef __KERNEL__, but that's OK because it has its own.

Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
---

threadalloc-dave/include/asm-generic/page.h | 29 +++++++++++++++++-
threadalloc-dave/mm/Kconfig | 44 ++++++++++++++++++++++++++++
2 files changed, 71 insertions(+), 2 deletions(-)

diff -puN include/asm-generic/page.h~generic-PAGE_SIZE-infrastructure include/asm-generic/page.h
--- threadalloc/include/asm-generic/page.h~generic-PAGE_SIZE-infrastructure 2006-08-31 13:48:45.000000000 -0700
+++ threadalloc-dave/include/asm-generic/page.h 2006-08-31 13:49:04.000000000 -0700
@@ -1,11 +1,36 @@
#ifndef _ASM_GENERIC_PAGE_H
#define _ASM_GENERIC_PAGE_H

+#include <linux/compiler.h>
+#include <linux/align.h>
+
#ifdef __KERNEL__
-#ifndef __ASSEMBLY__

-#include <linux/compiler.h>
+#ifdef __ASSEMBLY__
+#define ASM_CONST(x) x
+#else
+#define __ASM_CONST(x) x##UL
+#define ASM_CONST(x) __ASM_CONST(x)
+#endif
+
+#ifdef CONFIG_ARCH_GENERIC_PAGE_SIZE
+
+#define PAGE_SHIFT CONFIG_PAGE_SHIFT
+#define PAGE_SIZE (ASM_CONST(1) << PAGE_SHIFT)
+
+/*
+ * Subtle: (1 << PAGE_SHIFT) is an int, not an unsigned long. So if we
+ * assign PAGE_MASK to a larger type it gets extended the way we want
+ * (i.e. with 1s in the high bits)
+ */
+#define PAGE_MASK (~((1 << PAGE_SHIFT) - 1))

+/* to align the pointer to the (next) page boundary */
+#define PAGE_ALIGN(addr) ALIGN(addr, PAGE_SIZE)
+
+#endif /* CONFIG_ARCH_GENERIC_PAGE_SIZE */
+
+#ifndef __ASSEMBLY__
#ifndef CONFIG_ARCH_HAVE_GET_ORDER
/* Pure 2^n version of get_order */
static __inline__ __attribute_const__ int get_order(unsigned long size)
diff -puN mm/Kconfig~generic-PAGE_SIZE-infrastructure mm/Kconfig
--- threadalloc/mm/Kconfig~generic-PAGE_SIZE-infrastructure 2006-08-31 13:48:45.000000000 -0700
+++ threadalloc-dave/mm/Kconfig 2006-08-31 13:49:04.000000000 -0700
@@ -2,6 +2,50 @@ config ARCH_HAVE_GET_ORDER
def_bool y
depends on IA64 || PPC32 || XTENSA

+choice
+ prompt "Kernel page size"
+ depends on ARCH_GENERIC_PAGE_SIZE
+config PAGE_SIZE_4KB
+ bool "4KB"
+ help
+ The kernel page size determines the basic chunk of memory handled
+ by the Linux VM. If these pages are larger, the kernel can
+ use the same amount of physical memory with fewer data structures.
+ This reduces the VM overhead in handling large amounts of data.
+ Larger pages can also lead to better TLB coverage for large memory
+ applications.
+
+ However, larger pages also lead to memory being wasted by the
+ kernel since all files require a minimum of one page of memory.
+ With a 64KB page size, a 1 byte file will consume 64KB of memory.
+
+ A 4KB pagesize is fairly standard and may be required for 32-bit
+ compatibility on many platforms.
+
+ It is usually not wise to select another page size than the default.
+
+config PAGE_SIZE_8KB
+ bool "8KB"
+config PAGE_SIZE_16KB
+ bool "16KB"
+config PAGE_SIZE_64KB
+ bool "64KB"
+config PAGE_SIZE_512KB
+ bool "512KB"
+config PAGE_SIZE_4MB
+ bool "4MB"
+endchoice
+
+config PAGE_SHIFT
+ int
+ depends on ARCH_GENERIC_PAGE_SIZE
+ default "13" if PAGE_SIZE_8KB
+ default "14" if PAGE_SIZE_16KB
+ default "16" if PAGE_SIZE_64KB
+ default "19" if PAGE_SIZE_512KB
+ default "22" if PAGE_SIZE_4MB
+ default "12"
+
config SELECT_MEMORY_MODEL
def_bool y
depends on EXPERIMENTAL || ARCH_SELECT_MEMORY_MODEL
_