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Message-ID: <4A6DF0B6.7080402@bitwagon.com>
Date: Mon, 27 Jul 2009 11:23:50 -0700
From: John Reiser <jreiser@...wagon.com>
To: Steven Rostedt <rostedt@...dmis.org>,
Steven Rostedt <srostedt@...hat.com>,
Ingo Molnar <mingo@...e.hu>, Sam Ravnborg <sam@...nborg.org>,
Tejun Heo <tj@...nel.org>,
Frederic Weisbecker <fweisbec@...il.com>,
Li Zefan <lizf@...fujitsu.com>
CC: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: ftrace: __start_mcount_loc should be .init.rodata
__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.
[Please cc: me if replying only to the linux-kernel list.]
Signed off by: John Reiser <jreiser@...Wagon.com>
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)
--
--
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