linux-kernel - Re: [Patch v2] mm/memblock: discard .text/.data if CONFIG_ARCH_KEEP

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Date: Tue, 21 May 2024 10:21:52 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Wei Yang <richard.weiyang@...il.com>
Cc: mpe@...erman.id.au, npiggin@...il.com, christophe.leroy@...roup.eu,
	aneesh.kumar@...nel.org, naveen.n.rao@...ux.ibm.com, arnd@...db.de,
	anshuman.khandual@....com, linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [Patch v2] mm/memblock: discard .text/.data if
 CONFIG_ARCH_KEEP_MEMBLOCK not set

Hi,

On Fri, May 10, 2024 at 02:04:22AM +0000, 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.
> 
> 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, from the log message in mem_init_print_info(), init size
> increase from 2420K to 2432K on arch x86.
> 
> Signed-off-by: Wei Yang <richard.weiyang@...il.com>
> 
> ---
> v2: fix orphan section for powerpc
> ---
>  arch/powerpc/kernel/vmlinux.lds.S |  1 +
>  include/asm-generic/vmlinux.lds.h | 14 +++++++++++++-
>  include/linux/memblock.h          |  8 ++++----
>  3 files changed, 18 insertions(+), 5 deletions(-)
>  
> +#define __init_memblock        __section(".mbinit.text") __cold notrace \
> +						  __latent_entropy
> +#define __initdata_memblock    __section(".mbinit.data")
> +

The new .mbinit.* sections should be added to scripts/mod/modpost.c
alongside .meminit.* sections and then I expect modpost to report a bunch
of section mismatches because many memblock functions are called on memory
hotplug even on architectures that don't select ARCH_KEEP_MEMBLOCK.

>  #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
>  
> -- 
> 2.34.1
> 
> 

-- 
Sincerely yours,
Mike.