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:	Wed, 12 Aug 2009 08:31:03 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	kosaki.motohiro@...fujitsu.com,
	Larry Woodman <lwoodman@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>, riel@...hat.com,
	Peter Zijlstra <peterz@...radead.org>,
	Li Ming Chun <macli@....ubc.ca>,
	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

> The page allocation trace event reports that a page was successfully allocated
> but it does not specify where it came from. When analysing performance,
> it can be important to distinguish between pages coming from the per-cpu
> allocator and pages coming from the buddy lists as the latter requires the
> zone lock to the taken and more data structures to be examined.
> 
> This patch adds a trace event for __rmqueue reporting when a page is being
> allocated from the buddy lists. It distinguishes between being called
> to refill the per-cpu lists or whether it is a high-order allocation.
> Similarly, this patch adds an event to catch when the PCP lists are being
> drained a little and pages are going back to the buddy lists.
> 
> This is trickier to draw conclusions from but high activity on those
> events could explain why there were a large number of cache misses on a
> page-allocator-intensive workload. The coalescing and splitting of buddies
> involves a lot of writing of page metadata and cache line bounces not to
> mention the acquisition of an interrupt-safe lock necessary to enter this
> path.

Looks good to me.
	Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>



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