linux-kernel - Re: [PATCH v4 2/2] mm/page_ref: add tracepoint to track down page reference manipulation

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Date:	Mon, 7 Mar 2016 13:20:55 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Vlastimil Babka <vbabka@...e.cz>,
	Michal Nazarewicz <mina86@...a86.com>,
	Minchan Kim <minchan@...nel.org>,
	Mel Gorman <mgorman@...hsingularity.net>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-api@...r.kernel.org
Subject: Re: [PATCH v4 2/2] mm/page_ref: add tracepoint to track down page
 reference manipulation

On Fri, Mar 04, 2016 at 12:04:39PM -0800, Andrew Morton wrote:
> On Thu, 3 Mar 2016 16:43:49 +0900 Joonsoo Kim <js1304@...il.com> wrote:
> 
> > > Acked-by: Vlastimil Babka <vbabka@...e.cz>
> > >
> > >> +config DEBUG_PAGE_REF
> > >> +       bool "Enable tracepoint to track down page reference manipulation"
> > >> +       depends on DEBUG_KERNEL
> > >> +       depends on TRACEPOINTS
> > >> +       ---help---
> > >> +         This is the feature to add tracepoint for tracking down page
> > >> reference
> > >> +         manipulation. This tracking is useful to diagnosis functional
> > >> failure
> > >> +         due to migration failure caused by page reference mismatch. Be
> > >
> > >
> > > OK.
> > >
> > >> +         careful to turn on this feature because it could bloat some
> > >> kernel
> > >> +         text. In my configuration, it bloats 30 KB. Although kernel text
> > >> will
> > >> +         be bloated, there would be no runtime performance overhead if
> > >> +         tracepoint isn't enabled thanks to jump label.
> > >
> > >
> > > I would just write something like:
> > >
> > > Enabling this feature adds about 30 KB to the kernel code, but runtime
> > > performance overhead is virtually none until the tracepoints are actually
> > > enabled.
> > 
> > Okay, better!
> > Andrew, do you want fixup patch from me or could you simply handle it?
> > 
> 
> This?

Yep!

Thanks!

> 
> --- a/mm/Kconfig.debug~mm-page_ref-add-tracepoint-to-track-down-page-reference-manipulation-fix-3-fix
> +++ a/mm/Kconfig.debug
> @@ -82,10 +82,9 @@ config DEBUG_PAGE_REF
>  	depends on DEBUG_KERNEL
>  	depends on TRACEPOINTS
>  	---help---
> -	  This is the feature to add tracepoint for tracking down page reference
> -	  manipulation. This tracking is useful to diagnosis functional failure
> -	  due to migration failure caused by page reference mismatch. Be
> -	  careful to turn on this feature because it could bloat some kernel
> -	  text. In my configuration, it bloats 30 KB. Although kernel text will
> -	  be bloated, there would be no runtime performance overhead if
> -	  tracepoint isn't enabled thanks to jump label.
> +	  This is a feature to add tracepoint for tracking down page reference
> +	  manipulation. This tracking is useful to diagnose functional failure
> +	  due to migration failures caused by page reference mismatches.  Be
> +	  careful when enabling this feature because it adds about 30 KB to the
> +	  kernel code.  However the runtime performance overhead is virtually
> +	  nil until the tracepoints are actually enabled.
> _
> 
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