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

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Date:	Fri, 19 Feb 2016 10:39:10 +0900
From:	Joonsoo Kim <js1304@...il.com>
To:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Nazarewicz <mina86@...a86.com>,
	Minchan Kim <minchan@...nel.org>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Vlastimil Babka <vbabka@...e.cz>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	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 2/2] mm/page_ref: add tracepoint to track down page
 reference manipulation

2016-02-19 9:34 GMT+09:00 Sergey Senozhatsky
<sergey.senozhatsky.work@...il.com>:
> On (02/18/16 09:29), Steven Rostedt wrote:
>> > diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h
>> > index 534249c..fd6d9a5 100644
>> > --- a/include/linux/page_ref.h
>> > +++ b/include/linux/page_ref.h
>> > @@ -1,6 +1,54 @@
>> >  #include <linux/atomic.h>
>> >  #include <linux/mm_types.h>
>> >  #include <linux/page-flags.h>
>> > +#include <linux/tracepoint-defs.h>
>> > +
>> > +extern struct tracepoint __tracepoint_page_ref_set;
>> > +extern struct tracepoint __tracepoint_page_ref_mod;
>> > +extern struct tracepoint __tracepoint_page_ref_mod_and_test;
>> > +extern struct tracepoint __tracepoint_page_ref_mod_and_return;
>> > +extern struct tracepoint __tracepoint_page_ref_mod_unless;
>> > +extern struct tracepoint __tracepoint_page_ref_freeze;
>> > +extern struct tracepoint __tracepoint_page_ref_unfreeze;
>> > +
>> > +#ifdef CONFIG_DEBUG_PAGE_REF
>>
>> Please add a comment here. Something to the effect of:
>>
>> /*
>>  * Ideally we would want to use the trace_<tracepoint>_enabled() helper
>>  * functions. But due to include header file issues, that is not
>>  * feasible. Instead we have to open code the static key functions.
>>  *
>>  * See trace_##name##_enabled(void) in include/linux/tracepoint.h
>>  */
>>
>
> not sure if it's worth mentioning in the comment, but the other
> concern here is the performance impact of an extra function call,
> I believe. otherwise, Joonsoo would just do:

It's very natural thing so I'm not sure it is worth mentioning.

> in include/linux/page_ref.h
>
> static inline void set_page_count(struct page *page, int v)
> {
>         atomic_set(&page->_count, v);
>         __page_ref_set(page, v);
> }
> ...
>
>
>
> and in mm/debug_page_ref.c
>
> void __page_ref_set(struct page *page, int v)
> {
>         if (trace_page_ref_set_enabled())
>                 trace_page_ref_set(page, v);
> }
> EXPORT_SYMBOL(__page_ref_set);
> EXPORT_TRACEPOINT_SYMBOL(page_ref_set);

It is what I did in v1.

Thanks.