On Mon, May 06, 2024 at 03:30:54PM +0530, Anshuman Khandual wrote:
>
>On 5/6/24 06:51, Wei Yang wrote:
>> When CONFIG_ARCH_KEEP_MEMBLOCK not set, we expect to discard related
>> code and data. But it doesn't until CONFIG_MEMORY_HOTPLUG not set
>> neither.
>
>When CONFIG_ARCH_KEEP_MEMBLOCK is not set memblock information both for
>normal and reserved memory get freed up but should the memblock related
>code and data also be freed up as well ? Then I would also believe such
If not freed, those functions would access unpredictable area.
>memory saving will be very minimal given CONFIG_ARCH_KEEP_MEMBLOCK code
>is too limited scoped in the tree.
Not very much, it shows 12K more in it.
>
>Also could you please explain how it is related to CONFIG_MEMORY_HOTPLUG
>config being set or not.
>
This is in file include/asm-generic/vmlinux.lds.h.
MEM_KEEP/MEM_DISCARD is conditionally defined by CONFIG_MEMORY_HOTPLUG.
So even __init_memblock is defined as __meminit when CONFIG_ARCH_KEEP_MEMBLOCK
not set, it is not discarded.
>>
>> This patch puts memblock's .text/.data into its own section, so that it
>> only depends on CONFIG_ARCH_KEEP_MEMBLOCK to discard related code and
>> data. After this, init size increase from 2420K to 2432K.
>
>Is not this memory size saving some what insignificant to warrant a code
>change ? Also is this problem applicable only to CONFIG_ARCH_KEEP_MEMBLOCK
Yes, this is not significant.
>config. Could you also provide details on how did you measure these numbers ?
>
Kernel print related info in mem_init_print_info(). One of is it
init size, which includes init_data and init_text.
>>
>> Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx>
>> ---
>> include/asm-generic/vmlinux.lds.h | 14 +++++++++++++-
>> include/linux/memblock.h | 8 ++++----
>> 2 files changed, 17 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
>> index f7749d0f2562..775c5eedb9e6 100644
>> --- a/include/asm-generic/vmlinux.lds.h
>> +++ b/include/asm-generic/vmlinux.lds.h
>> @@ -147,6 +147,14 @@
>> #define MEM_DISCARD(sec) *(.mem##sec)
>> #endif
>>
>> +#if defined(CONFIG_ARCH_KEEP_MEMBLOCK)
>> +#define MEMBLOCK_KEEP(sec) *(.mb##sec)
>> +#define MEMBLOCK_DISCARD(sec)
>> +#else
>> +#define MEMBLOCK_KEEP(sec)
>> +#define MEMBLOCK_DISCARD(sec) *(.mb##sec)
>> +#endif
>> +
>> #ifndef CONFIG_HAVE_DYNAMIC_FTRACE_NO_PATCHABLE
>> #define KEEP_PATCHABLE KEEP(*(__patchable_function_entries))
>> #define PATCHABLE_DISCARDS
>> @@ -356,6 +364,7 @@
>> *(.ref.data) \
>> *(.data..shared_aligned) /* percpu related */ \
>> MEM_KEEP(init.data*) \
>> + MEMBLOCK_KEEP(init.data*) \
>> *(.data.unlikely) \
>> __start_once = .; \
>> *(.data.once) \
>> @@ -573,6 +582,7 @@
>> *(.ref.text) \
>> *(.text.asan.* .text.tsan.*) \
>> MEM_KEEP(init.text*) \
>> + MEMBLOCK_KEEP(init.text*) \
>>
>>
>> /* sched.text is aling to function alignment to secure we have same
>> @@ -680,6 +690,7 @@
>> KEEP(*(SORT(___kentry+*))) \
>> *(.init.data .init.data.*) \
>> MEM_DISCARD(init.data*) \
>> + MEMBLOCK_DISCARD(init.data*) \
>> KERNEL_CTORS() \
>> MCOUNT_REC() \
>> *(.init.rodata .init.rodata.*) \
>> @@ -706,7 +717,8 @@
>> #define INIT_TEXT \
>> *(.init.text .init.text.*) \
>> *(.text.startup) \
>> - MEM_DISCARD(init.text*)
>> + MEM_DISCARD(init.text*) \
>> + MEMBLOCK_DISCARD(init.text*)
>>
>> #define EXIT_DATA \
>> *(.exit.data .exit.data.*) \
>> diff --git a/include/linux/memblock.h b/include/linux/memblock.h
>> index e2082240586d..3e1f1d42dde7 100644
>> --- a/include/linux/memblock.h
>> +++ b/include/linux/memblock.h
>> @@ -100,13 +100,13 @@ struct memblock {
>>
>> extern struct memblock memblock;
>>
>> +#define __init_memblock __section(".mbinit.text") __cold notrace \
>> + __latent_entropy
>> +#define __initdata_memblock __section(".mbinit.data")
>> +
>> #ifndef CONFIG_ARCH_KEEP_MEMBLOCK
>> -#define __init_memblock __meminit
>> -#define __initdata_memblock __meminitdata
>> void memblock_discard(void);
>> #else
>> -#define __init_memblock
>> -#define __initdata_memblock
>> static inline void memblock_discard(void) {}
>> #endif
>>
--
Wei Yang
Help you, Help me
