Re: [PATCH v4 3/4] mm/memory.c: Add memory read privilege on page fault handling

[maobibo <maobibo@loongson.cn>]

On 05/20/2020 09:30 AM, Andrew Morton wrote:
> On Tue, 19 May 2020 18:03:29 +0800 Bibo Mao <maobibo@loongson.cn> wrote:
> 
>> Here add pte_sw_mkyoung function to make page readable on MIPS
>> platform during page fault handling. This patch improves page
>> fault latency about 10% on my MIPS machine with lmbench
>> lat_pagefault case.
>>
>> It is noop function on other arches, there is no negative
>> influence on those architectures.
>>
>> --- a/arch/mips/include/asm/pgtable.h
>> +++ b/arch/mips/include/asm/pgtable.h
>> @@ -414,6 +414,8 @@ static inline pte_t pte_mkyoung(pte_t pte)
>>  	return pte;
>>  }
>>  
>> +#define pte_sw_mkyoung	pte_mkyoung
>> +
>>  #ifdef CONFIG_MIPS_HUGE_TLB_SUPPORT
>>  static inline int pte_huge(pte_t pte)	{ return pte_val(pte) & _PAGE_HUGE; }
>>  
>> --- a/include/asm-generic/pgtable.h
>> +++ b/include/asm-generic/pgtable.h
>> @@ -227,6 +227,21 @@ static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addres
>>  }
>>  #endif
>>  
>> +/*
>> + * On some architectures hardware does not set page access bit when accessing
>> + * memory page, it is responsibilty of software setting this bit. It brings
>> + * out extra page fault penalty to track page access bit. For optimization page
>> + * access bit can be set during all page fault flow on these arches.
>> + * To be differentiate with macro pte_mkyoung, this macro is used on platforms
>> + * where software maintains page access bit.
>> + */
>> +#ifndef pte_sw_mkyoung
>> +static inline pte_t pte_sw_mkyoung(pte_t pte)
>> +{
>> +	return pte;
>> +}
>> +#endif
> 
> Yup, that's neat enough.  Thanks for making this change.  It looks like
> all architectures include asm-generic/pgtable.h so that's fine.
> 
> It's conventional to add a
> 
> #define pte_sw_mkyoung pte_sw_mkyoung
> 
> immediately above the #endif there, so we can't try to implement
> pte_sw_mkyoung() twice if this header gets included twice.  But the
> header has #ifndef _ASM_GENERIC_PGTABLE_H around the whole thing so
> that should be OK.

Sure, will do, and thanks for your kindly help and guidance