Re: [RFC] arm: add __initbss section attribute
From: yalin wang
Date: Mon Oct 12 2015 - 04:47:14 EST
> On Oct 12, 2015, at 16:22, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote:
>
> On 12 October 2015 at 05:59, yalin wang <yalin.wang2010@xxxxxxxxx> wrote:
>> This attribute can make init data to be into .initbss section,
>> this will make the data to be NO_BITS in vmlinux, can shrink the
>> Image file size, and speed up the boot up time.
>>
>> Signed-off-by: yalin wang <yalin.wang2010@xxxxxxxxx>
>> ---
>> arch/arm/kernel/vmlinux.lds.S | 2 +-
>> arch/arm/mm/init.c | 1 +
>> include/asm-generic/sections.h | 1 +
>> include/asm-generic/vmlinux.lds.h | 11 ++++++++++-
>> include/linux/init.h | 1 +
>> include/linux/mm.h | 4 +++-
>> 6 files changed, 17 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
>> index 8b60fde..ad6d740 100644
>> --- a/arch/arm/kernel/vmlinux.lds.S
>> +++ b/arch/arm/kernel/vmlinux.lds.S
>> @@ -330,7 +330,7 @@ SECTIONS
>> }
>> #endif
>>
>> - BSS_SECTION(0, 0, 0)
>> + BSS_SECTION(0, 0, 0, 0)
>> _end = .;
>>
>> STABS_DEBUG
>> diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
>> index 8a63b4c..50b881e 100644
>> --- a/arch/arm/mm/init.c
>> +++ b/arch/arm/mm/init.c
>> @@ -722,6 +722,7 @@ void free_initmem(void)
>> free_tcmmem();
>>
>> poison_init_mem(__init_begin, __init_end - __init_begin);
>> + poison_init_mem(__initbss_start, __initbss_start - __initbss_end);
>> if (!machine_is_integrator() && !machine_is_cintegrator())
>> free_initmem_default(-1);
>> }
>> diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h
>> index b58fd66..a63ebe9 100644
>> --- a/include/asm-generic/sections.h
>> +++ b/include/asm-generic/sections.h
>> @@ -29,6 +29,7 @@ extern char _text[], _stext[], _etext[];
>> extern char _data[], _sdata[], _edata[];
>> extern char __bss_start[], __bss_stop[];
>> extern char __init_begin[], __init_end[];
>> +extern char __initbss_start[], __initbss_end[];
>> extern char _sinittext[], _einittext[];
>> extern char _end[];
>> extern char __per_cpu_load[], __per_cpu_start[], __per_cpu_end[];
>> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
>> index c4bd0e2..b3db62d 100644
>> --- a/include/asm-generic/vmlinux.lds.h
>> +++ b/include/asm-generic/vmlinux.lds.h
>> @@ -574,6 +574,14 @@
>> *(COMMON) \
>> }
>>
>> +#define INITBSS(initbss_align) \
>> + . = ALIGN(initbss_align); \
>> + .initbss : AT(ADDR(.initbss) - LOAD_OFFSET) { \
>> + VMLINUX_SYMBOL(__initbss_start) = .; \
>> + *(.bss.init.data) \
>> + VMLINUX_SYMBOL(__initbss_end) = .; \
>> + }
>> +
>> /*
>> * DWARF debug sections.
>> * Symbols in the DWARF debugging sections are relative to
>> @@ -831,10 +839,11 @@
>> INIT_RAM_FS \
>> }
>>
>> -#define BSS_SECTION(sbss_align, bss_align, stop_align) \
>> +#define BSS_SECTION(sbss_align, bss_align, initbss_align, stop_align) \
>> . = ALIGN(sbss_align); \
>> VMLINUX_SYMBOL(__bss_start) = .; \
>> SBSS(sbss_align) \
>> BSS(bss_align) \
>> + INITBSS(initbss_align) \
>> . = ALIGN(stop_align); \
>> VMLINUX_SYMBOL(__bss_stop) = .;
>> diff --git a/include/linux/init.h b/include/linux/init.h
>> index b449f37..f2960b2 100644
>> --- a/include/linux/init.h
>> +++ b/include/linux/init.h
>> @@ -41,6 +41,7 @@
>> discard it in modules) */
>> #define __init __section(.init.text) __cold notrace
>> #define __initdata __section(.init.data)
>> +#define __initbss __section(.bss.init.data)
>
> Shouldn't this be .init.bss ?
>
>> #define __initconst __constsection(.init.rodata)
>> #define __exitdata __section(.exit.data)
>> #define __exit_call __used __section(.exitcall.exit)
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index d30eea3..1f266f7 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -21,6 +21,7 @@
>> #include <linux/resource.h>
>> #include <linux/page_ext.h>
>> #include <linux/err.h>
>> +#include <asm/sections.h>
>>
>> struct mempolicy;
>> struct anon_vma;
>> @@ -1722,10 +1723,11 @@ static inline void mark_page_reserved(struct page *page)
>> */
>> static inline unsigned long free_initmem_default(int poison)
>> {
>> - extern char __init_begin[], __init_end[];
>>
>> return free_reserved_area(&__init_begin, &__init_end,
>> poison, "unused kernel");
>> + return free_reserved_area(&__initbss_start, &__initbss_end,
>> + poison, "unused kernel");
>
> You obviously have not tested this code, since the first return makes
> the second unreachable.
>
> So you will need to put __initbss annotations all over the tree to
> actually populate and then free this section (after you have fixed
> your code). Before we do that, could we have an estimate of how much
> memory it actually frees up, especially since the zImage compression
> should ensure that zero initialized PROGBITS .data does not take very
> much additional space in the first place.
>
> --
> Ard.
yeah, I just compile it , not test it . because i need replace lots of __initdata variable to __initbss first .
i donât think zImage compression can shrink zero data in .data section ,
in current __initdata implementation , the zero initialized data are mixed with non-zero data,
for example:
int a = 20 __initdata;
int b __initdata; // zero initialized data
int c = 30 __initdata;
so the zero data are not in a contineous memory area, compress will not benefit from this scenario,
and on some platforms like arm64 , donât compress compress zImage ,
i will make a test in some time later, and send out the result to see if this method is better .
Thanks
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