Messages in this thread |  | | | Date | Mon, 27 Jul 2009 16:44:24 -0400 (EDT) | | From | Steven Rostedt <> | | Subject | Re: ftrace: __start_mcount_loc should be .init.rodata |
| |
On Mon, 27 Jul 2009, John Reiser wrote:
> __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.
Are you sure about that?
> > __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@BitWagon.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) { \
Isn't this in __init_rodata? Doesn't this get removed too?
I may be confused by all the uses of "init" in this file.
-- Steve
> *(.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) > > -- > >
|  |