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Date: Fri, 19 Feb 2016 10:39:10 +0900
Message-ID: <CAAmzW4Ni2uZ_J1dcfHPNPYDc0EDDDOL+_oKD-+OZ=Cmg=8sgGA@mail.gmail.com>
Subject: Re: [PATCH 2/2] mm/page_ref: add tracepoint to track down page
 reference manipulation
From: Joonsoo Kim <js1304@gmail.com>
To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Nazarewicz <mina86@mina86.com>,
        Minchan Kim <minchan@kernel.org>,
        Mel Gorman <mgorman@techsingularity.net>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>, linux-api@vger.kernel.org,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>
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2016-02-19 9:34 GMT+09:00 Sergey Senozhatsky
<sergey.senozhatsky.work@gmail.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.