linux-kernel - Re: [PATCH v4 1/5] mm: cma: add trace events to debug physically-contiguous memory allocations

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Date:	Tue, 17 Mar 2015 08:40:25 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Stefan Strogin <s.strogin@...tner.samsung.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Michal Nazarewicz <mina86@...a86.com>,
	aneesh.kumar@...ux.vnet.ibm.com,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Dmitry Safonov <d.safonov@...tner.samsung.com>,
	Pintu Kumar <pintu.k@...sung.com>,
	Weijie Yang <weijie.yang@...sung.com>,
	Laura Abbott <lauraa@...eaurora.org>,
	SeongJae Park <sj38.park@...il.com>,
	Hui Zhu <zhuhui@...omi.com>, Minchan Kim <minchan@...nel.org>,
	Dyasly Sergey <s.dyasly@...sung.com>,
	Vyacheslav Tyrtov <v.tyrtov@...sung.com>,
	Aleksei Mateosian <a.mateosian@...sung.com>,
	gregory.0xf0@...il.com, sasha.levin@...cle.com, gioh.kim@....com,
	pavel@....cz, stefan.strogin@...il.com,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v4 1/5] mm: cma: add trace events to debug
 physically-contiguous memory allocations


* Stefan Strogin <s.strogin@...tner.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
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