lkml.org 
[lkml]   [2009]   [Sep]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH 1/4] ftrace: __start_mcount_loc should be .init.rodata
From: John Reiser <jreiser@bitwagon.com>

__start_mcount_loc[] is unused after init, yet occupies RAM forever
as part of .rodata. 152kiB is typical on a 64-bit architecture. Instead,
__start_mcount_loc should be in the interval [__init_begin, __init_end)
so that the space is reclaimed after init.

__start_mcount_loc[] is generated during the load portion
of kernel build, and is used only by ftrace_init(). ftrace_init is declared
'__init' and is in .init.text, which is freed after init.
__start_mcount_loc is placed into .rodata by a call to MCOUNT_REC inside
the RO_DATA macro of include/asm-generic/vmlinux.lds.h. The array *is*
read-only, but more importantly it is not used after init. So the call to
MCOUNT_REC should be moved from RO_DATA to INIT_DATA.

This patch has been tested on x86_64 with CONFIG_DEBUG_PAGEALLOC=y
which verifies that the address range never is accessed after init.

Signed-off-by: John Reiser <jreiser@BitWagon.com>
LKML-Reference: <4A6DF0B6.7080402@bitwagon.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
include/asm-generic/vmlinux.lds.h | 5 +++--
1 files changed, 3 insertions(+), 2 deletions(-)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 6ad76bf..98b37cf 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -91,7 +91,8 @@
#endif

#ifdef CONFIG_FTRACE_MCOUNT_RECORD
-#define MCOUNT_REC() VMLINUX_SYMBOL(__start_mcount_loc) = .; \
+#define MCOUNT_REC() . = ALIGN(8); \
+ VMLINUX_SYMBOL(__start_mcount_loc) = .; \
*(__mcount_loc) \
VMLINUX_SYMBOL(__stop_mcount_loc) = .;
#else
@@ -331,7 +332,6 @@
/* __*init sections */ \
__init_rodata : AT(ADDR(__init_rodata) - LOAD_OFFSET) { \
*(.ref.rodata) \
- MCOUNT_REC() \
DEV_KEEP(init.rodata) \
DEV_KEEP(exit.rodata) \
CPU_KEEP(init.rodata) \
@@ -455,6 +455,7 @@
MEM_DISCARD(init.data) \
KERNEL_CTORS() \
*(.init.rodata) \
+ MCOUNT_REC() \
DEV_DISCARD(init.rodata) \
CPU_DISCARD(init.rodata) \
MEM_DISCARD(init.rodata)
--
1.6.3.3
--


\
 
 \ /
  Last update: 2009-09-13 05:09    [from the cache]
©2003-2011 Jasper Spaans