linux-kernel - Re: [PATCH 06/14] Export fragmentation index via /proc/extfrag

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Message-Id: <20100406170542.fe9b9f33.akpm@linux-foundation.org>
Date:	Tue, 6 Apr 2010 17:05:42 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 06/14] Export fragmentation index via
 /proc/extfrag_index

On Fri,  2 Apr 2010 17:02:40 +0100
Mel Gorman <mel@....ul.ie> wrote:

> Fragmentation index is a value that makes sense when an allocation of a
> given size would fail. The index indicates whether an allocation failure is
> due to a lack of memory (values towards 0) or due to external fragmentation
> (value towards 1).  For the most part, the huge page size will be the size
> of interest but not necessarily so it is exported on a per-order and per-zone
> basis via /proc/extfrag_index

(/proc/sys/vm?)

Like unusable_index, this seems awfully specialised.  Perhaps we could
hide it under CONFIG_MEL, or even put it in debugfs with the intention
of removing it in 6 or 12 months time.  Either way, it's hard to
justify permanently adding this stuff to every kernel in the world?


I have a suspicion that all the info in unusable_index and
extfrag_index could be computed from userspace using /proc/kpageflags
(and perhaps a bit of dmesg-diddling to find the zones).  If that can't
be done today, I bet it'd be pretty easy to arrange for it.


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