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
memory saving will be very minimal given CONFIG_ARCH_KEEP_MEMBLOCK code
is too limited scoped in the tree.
Also could you please explain how it is related to CONFIG_MEMORY_HOTPLUG
config being set or not.
>
> 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
config. Could you also provide details on how did you measure these numbers ?
>
> 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
>
