Subject: Re: [PATCH] powerpc/64s/radix: Enable huge vmalloc mappings

From: Nicholas Piggin <[email-masked]>
Date: Sun, 02 May 2021 20:41:37 +1000

Excerpts from Christophe Leroy's message of May 2, 2021 5:34 pm:
> 
> 
> Le 02/05/2021 à 06:56, Nicholas Piggin a écrit :
>> This reduces TLB misses by nearly 30x on a `git diff` workload on a
>> 2-node POWER9 (59,800 -> 2,100) and reduces CPU cycles by 0.54%, due
>> to vfs hashes being allocated with 2MB pages.
>> 
>> Acked-by: Michael Ellerman <[email-masked]>
>> Signed-off-by: Nicholas Piggin <[email-masked]>
>> ---
>> This was in the -mm tree but was dropped at the last minute after
>> clashing with a patch in powerpc next.
>> 
>> Now all prerequisites are upstream, this can be merged as is. Probably
>> makes sense now to go via powerpc tree.
>> 
>> This is rebased and retested on upstream.
>> 
>>   Documentation/admin-guide/kernel-parameters.txt |  2 ++
>>   arch/powerpc/Kconfig                            |  1 +
>>   arch/powerpc/include/asm/pgtable.h              |  5 +++++
>>   arch/powerpc/kernel/module.c                    | 16 +++++++++++++---
>>   4 files changed, 21 insertions(+), 3 deletions(-)
>> 
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index 1c0a3cf6fcc9..1be38b25c485 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -3250,6 +3250,8 @@
>>   
>>   	nohugeiomap	[KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings.
>>   
>> +	nohugevmalloc	[PPC] Disable kernel huge vmalloc mappings.
>> +
>>   	nosmt		[KNL,S390] Disable symmetric multithreading (SMT).
>>   			Equivalent to smt=1.
>>   
>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
>> index 1e6230bea09d..c547a9d6a2dd 100644
>> --- a/arch/powerpc/Kconfig
>> +++ b/arch/powerpc/Kconfig
>> @@ -185,6 +185,7 @@ config PPC
>>   	select GENERIC_VDSO_TIME_NS
>>   	select HAVE_ARCH_AUDITSYSCALL
>>   	select HAVE_ARCH_HUGE_VMAP		if PPC_BOOK3S_64 && PPC_RADIX_MMU
>> +	select HAVE_ARCH_HUGE_VMALLOC		if HAVE_ARCH_HUGE_VMAP
>>   	select HAVE_ARCH_JUMP_LABEL
>>   	select HAVE_ARCH_JUMP_LABEL_RELATIVE
>>   	select HAVE_ARCH_KASAN			if PPC32 && PPC_PAGE_SHIFT <= 14
>> diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
>> index c6a676714f04..1678e4b08fc3 100644
>> --- a/arch/powerpc/include/asm/pgtable.h
>> +++ b/arch/powerpc/include/asm/pgtable.h
>> @@ -39,6 +39,11 @@ struct mm_struct;
>>   #define __S110	PAGE_SHARED_X
>>   #define __S111	PAGE_SHARED_X
>>   
>> +#ifndef MODULES_VADDR
>> +#define MODULES_VADDR	VMALLOC_START
>> +#define MODULES_END	VMALLOC_END
>> +#endif
> 
> This will also require some changes in a few places, see 
> https://patchwork.ozlabs.org/project/linuxppc-dev/patch/[email-masked]/

I see.

I'll just make the PPC64 version use VMALLOC_START/VMALLOC_END, which
avoids that stupid compiler warning found by kbuild robot as well.

> 
>> +
>>   #ifndef __ASSEMBLY__
>>   
>>   /* Keep these as a macros to avoid include dependency mess */
>> diff --git a/arch/powerpc/kernel/module.c b/arch/powerpc/kernel/module.c
>> index fab84024650c..77aefcbbd276 100644
>> --- a/arch/powerpc/kernel/module.c
>> +++ b/arch/powerpc/kernel/module.c
>> @@ -8,6 +8,7 @@
>>   #include <linux/moduleloader.h>
>>   #include <linux/err.h>
>>   #include <linux/vmalloc.h>
>> +#include <linux/mm.h>
>>   #include <linux/bug.h>
>>   #include <asm/module.h>
>>   #include <linux/uaccess.h>
>> @@ -88,17 +89,24 @@ int module_finalize(const Elf_Ehdr *hdr,
>>   	return 0;
>>   }
>>   
>> -#ifdef MODULES_VADDR
>>   static __always_inline void *
>>   __module_alloc(unsigned long size, unsigned long start, unsigned long end)
>>   {
>> +	/*
>> +	 * Don't do huge page allocations for modules yet until more testing
>> +	 * is done. STRICT_MODULE_RWX may require extra work to support this
>> +	 * too.
>> +	 */
>>   	return __vmalloc_node_range(size, 1, start, end, GFP_KERNEL,
>> -				    PAGE_KERNEL_EXEC, VM_FLUSH_RESET_PERMS, NUMA_NO_NODE,
>> +				    PAGE_KERNEL_EXEC,
>> +				    VM_FLUSH_RESET_PERMS | VM_NO_HUGE_VMAP,
>> +				    NUMA_NO_NODE,
>>   				    __builtin_return_address(0));
> 
> Can we avoid so many lines ? Doesn't it fit on 3 lines now that 100 chars per line are tolerated ?

It could be squashed onto fewer lines. Is it better?

> 
>>   }
>>   
>>   void *module_alloc(unsigned long size)
>>   {
>> +#ifdef CONFIG_PPC32
> 
> Can we just add an IS_ENABLED(CONFIG_PPC32) in the 'if' instead of this #ifdef/#else ?

I guess not if I don't define MODULES_VADDR. Jordan's clenup patch could 
change it to IS_ENABLED.

Thanks,
Nick

> 
>>   	unsigned long limit = (unsigned long)_etext - SZ_32M;
>>   	void *ptr = NULL;
>>   
>> @@ -112,5 +120,7 @@ void *module_alloc(unsigned long size)
>>   		ptr = __module_alloc(size, MODULES_VADDR, MODULES_END);
>>   
>>   	return ptr;
>> -}
>> +#else
>> +	return __module_alloc(size, MODULES_VADDR, MODULES_END);
>>   #endif
>> +}
>> 
>