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Date: Tue, 17 Mar 2015 08:40:25 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Stefan Strogin <s.strogin@partner.samsung.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
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        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Dmitry Safonov <d.safonov@partner.samsung.com>,
        Pintu Kumar <pintu.k@samsung.com>,
        Weijie Yang <weijie.yang@samsung.com>,
        Laura Abbott <lauraa@codeaurora.org>,
        SeongJae Park <sj38.park@gmail.com>, Hui Zhu <zhuhui@xiaomi.com>,
        Minchan Kim <minchan@kernel.org>, Dyasly Sergey <s.dyasly@samsung.com>,
        Vyacheslav Tyrtov <v.tyrtov@samsung.com>,
        Aleksei Mateosian <a.mateosian@samsung.com>, gregory.0xf0@gmail.com,
        sasha.levin@oracle.com, gioh.kim@lge.com, pavel@ucw.cz,
        stefan.strogin@gmail.com, Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>
Subject: Re: [PATCH v4 1/5] mm: cma: add trace events to debug
 physically-contiguous memory allocations
Message-ID: <20150317074025.GA27548@gmail.com>
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* Stefan Strogin <s.strogin@partner.samsung.com> wrote:

> > +TRACE_EVENT(cma_alloc,
> > +
> > +	TP_PROTO(struct cma *cma, struct page *page, int count),
> > +
> > +	TP_ARGS(cma, page, count),
> > +
> > +	TP_STRUCT__entry(
> > +		__field(struct page *, page)
> > +		__field(unsigned long, count)
> > +	),
> > +
> > +	TP_fast_assign(
> > +		__entry->page = page;
> > +		__entry->count = count;
> > +	),
> > +
> > +	TP_printk("page=%p pfn=%lu count=%lu",
> > +		  __entry->page,
> > +		  __entry->page ? page_to_pfn(__entry->page) : 0,
> > +		  __entry->count)

So I'm wondering, the fast-assign side is not equivalent to the 
TP_printk() side:

> > +		__entry->page = page;
> > +		  __entry->page ? page_to_pfn(__entry->page) : 0,

to me it seems it would be useful if MM tracing standardized on pfn 
printing. Just like you did for trace_cma_release().

Also:

> > +		  __entry->page ? page_to_pfn(__entry->page) : 0,

pfn 0 should probably be reserved for the true 0th pfn - those exist 
in some machines. Returning -1ll could be the 'no such pfn' condition?

> > +	TP_STRUCT__entry(
> > +		__field(unsigned long, pfn)

Btw., does pfn always fit into 32 bits on 32-bit platforms?

> > +		__field(unsigned long, count)

Does this have to be 64-bit on 64-bit platforms?

> > +	),
> > +
> > +	TP_fast_assign(
> > +		__entry->pfn = pfn;
> > +		__entry->count = count;
> > +	),
> > +
> > +	TP_printk("pfn=%lu page=%p count=%lu",
> > +		  __entry->pfn,
> > +		  pfn_to_page(__entry->pfn),
> > +		  __entry->count)

So here you print more in the TP_printk() line than in the fast-assign 
side.

Again I'd double check the various boundary conditions.

Thanks,

	Ingo