linux-kernel - Re: [PATCH 3/6] tracing, page-allocator: Add trace event for page traffic related to the buddy lists

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Date:	Fri, 7 Aug 2009 09:53:17 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Larry Woodman <lwoodman@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>, riel@...hat.com,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [PATCH 3/6] tracing, page-allocator: Add trace event for page
	traffic related to the buddy lists


* Mel Gorman <mel@....ul.ie> wrote:

> +TRACE_EVENT(mm_page_pcpu_drain,
> +
> +	TP_PROTO(struct page *page, int order, int migratetype),
> +
> +	TP_ARGS(page, order, migratetype),
> +
> +	TP_STRUCT__entry(
> +		__field(	struct page *,	page		)
> +		__field(	int,		order		)
> +		__field(	int,		migratetype	)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->page		= page;
> +		__entry->order		= order;
> +		__entry->migratetype	= migratetype;
> +	),
> +
> +	TP_printk("page=%p pfn=%lu order=%d cpu=%d migratetype=%d",
> +		__entry->page,
> +		page_to_pfn(__entry->page),
> +		__entry->order,
> +		smp_processor_id(),
> +		__entry->migratetype)

> +	trace_mm_page_alloc_zone_locked(page, order, migratetype, order == 0);

This can be optimized further by omitting the migratetype field and 
adding something like this:

	TP_printk("page=%p pfn=%lu order=%d cpu=%d migratetype=%d",
		__entry->page,
		page_to_pfn(__entry->page),
		__entry->order,
		smp_processor_id(),
		__entry->order == 0);

The advantage is 4 bytes less in the record and a shorter tracepoint 
fast-path - while still having the same output.

	Ingo
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