linux-kernel - Re: [PATCH 3/3] introduce HIGH_ORDER delineating easily reclaimable orders

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Message-Id: <20070421012843.f5a814eb.akpm@linux-foundation.org>
Date:	Sat, 21 Apr 2007 01:28:43 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andy Whitcroft <apw@...dowen.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Mel Gorman <mel@....ul.ie>
Subject: Re: [PATCH 3/3] introduce HIGH_ORDER delineating easily reclaimable
 orders

On Fri, 20 Apr 2007 16:04:36 +0100 Andy Whitcroft <apw@...dowen.org> wrote:

> The memory allocator treats lower order (order <= 3) and higher order
> (order >= 4) allocations in slightly different ways.  As lower orders
> are much more likely to be available and also more likely to be
> simply reclaimed it is deemed reasonable to wait longer for those.
> Lumpy reclaim also changes behaviour at this same boundary, more
> agressivly targetting pages in reclaim at higher order.
> 
> This patch removes all these magical numbers and replaces with
> with a constant HIGH_ORDER.

oh, there we go.

It would have been better to have patched page_alloc.c independently, then
to have used HIGH_ORDER in "lumpy: increase pressure at the end of the inactive
list".

The name HIGH_ORDER is a bit squidgy.  I'm not sure what would be better though.
PAGE_ALLOC_CLUSTER_MAX?

It'd be interesting to turn this into a runtime tunable, perhaps.
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