linux-kernel - Re: [PATCH 2/4] tracing, mm: Add trace events for anti-fragmentation falling back to other migratetypes

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Message-Id: <20090805182518.5BD0.A69D9226@jp.fujitsu.com>
Date:	Wed,  5 Aug 2009 18:26:32 +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>,
	Andrew Morton <akpm@...ux-foundation.org>, riel@...hat.com,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [PATCH 2/4] tracing, mm: Add trace events for anti-fragmentation falling back to other migratetypes

> Fragmentation avoidance depends on being able to use free pages from
> lists of the appropriate migrate type. In the event this is not
> possible, __rmqueue_fallback() selects a different list and in some
> circumstances change the migratetype of the pageblock. Simplistically,
> the more times this event occurs, the more likely that fragmentation
> will be a problem later for hugepage allocation at least but there are
> other considerations such as the order of page being split to satisfy
> the allocation.
> 
> This patch adds a trace event for __rmqueue_fallback() that reports what
> page is being used for the fallback, the orders of relevant pages, the
> desired migratetype and the migratetype of the lists being used, whether
> the pageblock changed type and whether this event is important with
> respect to fragmentation avoidance or not. This information can be used
> to help analyse fragmentation avoidance and help decide whether
> min_free_kbytes should be increased or not.
> 
> Signed-off-by: Mel Gorman <mel@....ul.ie>
> Acked-by: Rik van Riel <riel@...hat.com>

Looks good to me.
but I don't put my reviewed-by because I am not so familiar this area.



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