linux-kernel - Re: [PATCH v3 2/7] mm/gup: add gup trace points

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Message-ID: <20151208152555.1c03ae54@gandalf.local.home>
Date:	Tue, 8 Dec 2015 15:25:55 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Yang Shi <yang.shi@...aro.org>
Cc:	akpm@...ux-foundation.org, mingo@...hat.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linaro-kernel@...ts.linaro.org
Subject: Re: [PATCH v3 2/7] mm/gup: add gup trace points

On Tue,  8 Dec 2015 11:39:50 -0800
Yang Shi <yang.shi@...aro.org> wrote:

> For slow version, just add trace point for raw __get_user_pages since all
> slow variants call it to do the real work finally.
> 
> Signed-off-by: Yang Shi <yang.shi@...aro.org>
> ---
>  mm/gup.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index deafa2c..44f05c9 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -18,6 +18,9 @@
>  
>  #include "internal.h"
>  
> +#define CREATE_TRACE_POINTS
> +#include <trace/events/gup.h>
> +
>  static struct page *no_page_table(struct vm_area_struct *vma,
>  		unsigned int flags)
>  {
> @@ -462,6 +465,8 @@ long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
>  	if (!nr_pages)
>  		return 0;
>  
> +	trace_gup_get_user_pages(start, nr_pages);
> +
>  	VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));
>  
>  	/*
> @@ -599,6 +604,7 @@ int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
>  	if (!(vm_flags & vma->vm_flags))
>  		return -EFAULT;
>  
> +	trace_gup_fixup_user_fault(address);
>  	ret = handle_mm_fault(mm, vma, address, fault_flags);
>  	if (ret & VM_FAULT_ERROR) {
>  		if (ret & VM_FAULT_OOM)
> @@ -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, (unsigned long) nr_pages);

typecast shouldn't be needed. But I'm wondering, it would save space in
the ring buffer if we used unsigend int instead of long. Will nr_pages
ever be bigger than 4 billion?

-- Steve

> +
>  	/*
>  	 * Disable interrupts.  We use the nested form as we can already have
>  	 * interrupts disabled by get_futex_key.

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