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

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Date: Fri, 24 May 2024 01:46:56 +0000
From: Wei Yang <richard.weiyang@...il.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: Wei Yang <richard.weiyang@...il.com>, 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

On Tue, May 21, 2024 at 10:21:52AM +0300, Mike Rapoport wrote:
>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.
>

I tried to add some code in modpost.c, "make all" looks good.

May I ask how can I trigger the "mismatch" warning?

BTW, if ARCH_KEEP_MEMBLOCK unset, we would discard memblock meta-data. If
hotplug would call memblock function, it would be dangerous?

The additional code I used is like below.

---
 scripts/mod/modpost.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 937294ff164f..c837e2882904 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -777,14 +777,14 @@ static void check_section(const char *modname, struct elf_info *elf,
 
 #define ALL_INIT_DATA_SECTIONS \
 	".init.setup", ".init.rodata", ".meminit.rodata", \
-	".init.data", ".meminit.data"
+	".init.data", ".meminit.data", "mbinit.data"
 
 #define ALL_PCI_INIT_SECTIONS	\
 	".pci_fixup_early", ".pci_fixup_header", ".pci_fixup_final", \
 	".pci_fixup_enable", ".pci_fixup_resume", \
 	".pci_fixup_resume_early", ".pci_fixup_suspend"
 
-#define ALL_XXXINIT_SECTIONS ".meminit.*"
+#define ALL_XXXINIT_SECTIONS ".meminit.*", "mbinit.*"
 
 #define ALL_INIT_SECTIONS INIT_SECTIONS, ALL_XXXINIT_SECTIONS
 #define ALL_EXIT_SECTIONS ".exit.*"
@@ -799,7 +799,7 @@ static void check_section(const char *modname, struct elf_info *elf,
 
 #define INIT_SECTIONS      ".init.*"
 
-#define ALL_TEXT_SECTIONS  ".init.text", ".meminit.text", ".exit.text", \
+#define ALL_TEXT_SECTIONS  ".init.text", ".meminit.text", ".mbinit.text", ".exit.text", \
 		TEXT_SECTIONS, OTHER_TEXT_SECTIONS
 
 enum mismatch {
-- 
2.34.1


>>  #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.

-- 
Wei Yang
Help you, Help me