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Date:   Thu, 11 Apr 2019 09:02:30 +0800
From:   "Li, Aubrey" <aubrey.li@...ux.intel.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>, aubrey.li@...el.com,
        Linux API <linux-api@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v14 1/3] /proc/pid/status: Add support for architecture
 specific output

On 2019/4/10 22:54, Andy Lutomirski wrote:
> On Tue, Apr 9, 2019 at 8:40 PM Li, Aubrey <aubrey.li@...ux.intel.com> wrote:
>>
>> On 2019/4/10 10:36, Li, Aubrey wrote:
>>> On 2019/4/10 10:25, Andy Lutomirski wrote:
>>>> On Tue, Apr 9, 2019 at 7:20 PM Li, Aubrey <aubrey.li@...ux.intel.com> wrote:
>>>>>
>>>>> On 2019/4/10 9:58, Andy Lutomirski wrote:
>>>>>> On Tue, Apr 9, 2019 at 6:55 PM Aubrey Li <aubrey.li@...ux.intel.com> wrote:
>>>>>>>
>>>>>>> The architecture specific information of the running processes could
>>>>>>> be useful to the userland. Add support to examine process architecture
>>>>>>> specific information externally.
>>>>>>>
>>>>>>> Signed-off-by: Aubrey Li <aubrey.li@...ux.intel.com>
>>>>>>> Cc: Peter Zijlstra <peterz@...radead.org>
>>>>>>> Cc: Andi Kleen <ak@...ux.intel.com>
>>>>>>> Cc: Tim Chen <tim.c.chen@...ux.intel.com>
>>>>>>> Cc: Dave Hansen <dave.hansen@...el.com>
>>>>>>> Cc: Arjan van de Ven <arjan@...ux.intel.com>
>>>>>>> Cc: Linux API <linux-api@...r.kernel.org>
>>>>>>> Cc: Alexey Dobriyan <adobriyan@...il.com>
>>>>>>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>>>>>>> ---
>>>>>>>  fs/proc/array.c         | 5 +++++
>>>>>>>  include/linux/proc_fs.h | 2 ++
>>>>>>>  2 files changed, 7 insertions(+)
>>>>>>>
>>>>>>> diff --git a/fs/proc/array.c b/fs/proc/array.c
>>>>>>> index 2edbb657f859..331592a61718 100644
>>>>>>> --- a/fs/proc/array.c
>>>>>>> +++ b/fs/proc/array.c
>>>>>>> @@ -401,6 +401,10 @@ static inline void task_thp_status(struct seq_file *m, struct mm_struct *mm)
>>>>>>>         seq_printf(m, "THP_enabled:\t%d\n", thp_enabled);
>>>>>>>  }
>>>>>>>
>>>>>>> +void __weak arch_proc_pid_status(struct seq_file *m, struct task_struct *task)
>>>>>>> +{
>>>>>>> +}
>>>>>>
>>>>>> This pointlessly bloats other architectures.  Do this instead in an
>>>>>> appropriate header:
>>>>>>
>>>>>> #ifndef arch_proc_pid_status
>>>>>> static inline void arch_proc_pid_status(...)
>>>>>> {
>>>>>> }
>>>>>> #endif
>>>>>>
>>>>>
>>>>> I saw a bunch of similar weak functions, is it not acceptable?
>>>>>
>>>>> fs/proc$ grep weak *.c
>>>>> cpuinfo.c:__weak void arch_freq_prepare_all(void)
>>>>> meminfo.c:void __attribute__((weak)) arch_report_meminfo(struct seq_file *m)
>>>>> vmcore.c:int __weak elfcorehdr_alloc(unsigned long long *addr, unsigned long long *size)
>>>>> vmcore.c:void __weak elfcorehdr_free(unsigned long long addr)
>>>>> vmcore.c:ssize_t __weak elfcorehdr_read(char *buf, size_t count, u64 *ppos)
>>>>> vmcore.c:ssize_t __weak elfcorehdr_read_notes(char *buf, size_t count, u64 *ppos)
>>>>> vmcore.c:int __weak remap_oldmem_pfn_range(struct vm_area_struct *vma,
>>>>> vmcore.c:ssize_t __weak
>>>>
>>>> I think they're acceptable, but I don't personally like them.
>>>>
>>>
>>> okay, let me try to see if I can refine it in an appropriate way.
>>
>> Hi Andy,
>>
>> Is this what you want?
>>
>> Thanks,
>> -Aubrey
>>
>> ====================================================================
>> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
>> index 2bb3a648fc12..82d77d3aefff 100644
>> --- a/arch/x86/include/asm/processor.h
>> +++ b/arch/x86/include/asm/processor.h
>> @@ -990,5 +990,8 @@ enum l1tf_mitigations {
>>  };
>>
>>  extern enum l1tf_mitigations l1tf_mitigation;
>> +/* Add support for architecture specific output in /proc/pid/status */
>> +void arch_proc_pid_status(struct seq_file *m, struct task_struct *task);
>> +#define arch_proc_pid_status arch_proc_pid_status
>>
>>  #endif /* _ASM_X86_PROCESSOR_H */
>> diff --git a/fs/proc/array.c b/fs/proc/array.c
>> index 2edbb657f859..fd65a6ba2864 100644
>> --- a/fs/proc/array.c
>> +++ b/fs/proc/array.c
>> @@ -401,6 +401,11 @@ static inline void task_thp_status(struct seq_file *m, struct mm_struct *mm)
>>         seq_printf(m, "THP_enabled:\t%d\n", thp_enabled);
>>  }
>>
>> +/* Add support for architecture specific output in /proc/pid/status */
>> +#ifndef arch_proc_pid_status
>> +#define arch_proc_pid_status(m, task)
>> +#endif
>> +
>>  int proc_pid_status(struct seq_file *m, struct pid_namespace *ns,
>>                         struct pid *pid, struct task_struct *task)
>>  {
>> @@ -424,6 +429,7 @@ int proc_pid_status(struct seq_file *m, struct pid_namespace *ns,
>>         task_cpus_allowed(m, task);
>>         cpuset_task_status_allowed(m, task);
>>         task_context_switch_counts(m, task);
>> +       arch_proc_pid_status(m, task);
>>         return 0;
>>  }
>>
> 
> Yes.  But I still think it would be nicer to separate the arch stuff
> into its own file.  Others might reasonably disagree with me.
> 
I like arch_status, I proposed but no other arch shows interesting in it.

I think the problem is similar for x86_status, it does not make sense for
those x86 platform without AVX512 to have an empty arch file. I personally
don't like [arch]_status because the code may become unclean if more arches
added in future.

Maybe it's too early to have a separated arch staff file for now.

Thanks,
-Aubrey

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