linux-kernel - Re: [PATCH 1/6] tracing, page-allocator: Add trace events for page allocation and page freeing

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Message-ID: <20090807075030.GB20292@elte.hu>
Date:	Fri, 7 Aug 2009 09:50:30 +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 1/6] tracing, page-allocator: Add trace events for page
	allocation and page freeing


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

> +TRACE_EVENT(mm_pagevec_free,

> +	TP_fast_assign(
> +		__entry->page		= page;
> +		__entry->order		= order;
> +		__entry->cold		= cold;
> +	),

> -	while (--i >= 0)
> +	while (--i >= 0) {
> +		trace_mm_pagevec_free(pvec->pages[i], 0, pvec->cold);
>  		free_hot_cold_page(pvec->pages[i], pvec->cold);
> +	}

Pagevec freeing has order 0 implicit, so you can further optimize 
this by leaving out the 'order' field and using this format string:

+	TP_printk("page=%p pfn=%lu order=0 cold=%d",
+                       __entry->page,
+                       page_to_pfn(__entry->page),
+                       __entry->cold)

the trace record becomes smaller by 4 bytes and the tracepoint 
fastpath becomes shorter as well.

	Ingo
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