linux-kernel - Re: [PATCH] Add __GFP_MOVABLE for callers to flag allocations that may be migrated

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Message-ID: <Pine.LNX.4.64.0612050754560.11213@schroedinger.engr.sgi.com>
Date:	Tue, 5 Dec 2006 08:00:39 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Andrew Morton <akpm@...l.org>
cc:	Mel Gorman <mel@...net.ie>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Add __GFP_MOVABLE for callers to flag allocations that
 may be migrated

On Mon, 4 Dec 2006, Andrew Morton wrote:

> > > What happens when we need to run reclaim against just a section of a zone?
> > > Lumpy-reclaim could be used here; perhaps that's Mel's approach too?
> > 
> > Why would we run reclaim against a section of a zone?
> 
> Strange question.  Because all the pages are in use for something else.

We always run reclaim against the whole zone not against parts. Why 
would we start running reclaim against a portion of a zone?

> > Mel aready has that for anti-frag. The sections are per MAX_ORDER area 
> > and the only states are movable unmovable and reclaimable. There is 
> > nothing more to it. No other state information should be added. Why would 
> > we need sub zones? For what purpose?
> 
> You're proposing that for memory hot-unplug, we take a single zone and by
> some means subdivide that into sections which correspond to physically
> hot-unpluggable memory.  That certainly does not map onto MAX_ORDER
> sections.

Mel's patches are already managing "sections" (if you want to call it 
that) of a zone in units of MAX_ORDER. If we memorize where the lowest 
unmovable MAX_ORDER block is then we have the necessary separation and can 
do memory unplug on the remainder of the zone.

> > What feature are you talking about?
> 
> Memory hot-unplug, of course.

There are multiple issues that we discuss here. Please be clear. 
Categorical demands for perfection certainly wont help us.
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