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

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Message-Id: <20160304120439.a38a15e0fe5b989fe5b8edfc@linux-foundation.org>
Date:	Fri, 4 Mar 2016 12:04:39 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Joonsoo Kim <js1304@...il.com>
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,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v4 2/2] mm/page_ref: add tracepoint to track down page
 reference manipulation

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?

--- 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.
_