linux-kernel - Re: [PATCH V2 2/7] mm/gup: add gup trace points

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Date:	Wed, 02 Dec 2015 16:11:37 -0800
From:	"Shi, Yang" <yang.shi@...aro.org>
To:	Dave Hansen <dave.hansen@...el.com>, akpm@...ux-foundation.org,
	rostedt@...dmis.org, mingo@...hat.com
CC:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linaro-kernel@...ts.linaro.org
Subject: Re: [PATCH V2 2/7] mm/gup: add gup trace points

On 12/2/2015 3:36 PM, Dave Hansen wrote:
> On 12/02/2015 02:53 PM, Yang Shi wrote:
>> diff --git a/mm/gup.c b/mm/gup.c
>> index deafa2c..10245a4 100644
>> --- a/mm/gup.c
>> +++ b/mm/gup.c
>> @@ -13,6 +13,9 @@
>>   #include <linux/rwsem.h>
>>   #include <linux/hugetlb.h>
>>
>> +#define CREATE_TRACE_POINTS
>> +#include <trace/events/gup.h>
>> +
>>   #include <asm/pgtable.h>
>>   #include <asm/tlbflush.h>
>
> This needs to be _the_ last thing that gets #included.  Otherwise, you
> risk colliding with any other trace header that gets implicitly included
> below.

Thanks for the suggestion, will move it to the last.

>
>> @@ -1340,6 +1346,8 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
>>   					start, len)))
>>   		return 0;
>>
>> +	trace_gup_get_user_pages_fast(start, nr_pages, write, pages);
>> +
>>   	/*
>>   	 * Disable interrupts.  We use the nested form as we can already have
>>   	 * interrupts disabled by get_futex_key.
>
> It would be _really_ nice to be able to see return values from the
> various gup calls as well.  Is that feasible?

I think it should be feasible. kmem_cache_alloc trace event could show 
return value. I'm supposed gup trace events should be able to do the 
same thing.

Regards,
Yang

>

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