linux-kernel - Re: [PATCH 1/3] page-allocator: Under memory pressure, wait on pressure to relieve instead of congestion

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Date:	Tue, 9 Mar 2010 11:11:55 -0600 (CST)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Mel Gorman <mel@....ul.ie>
cc:	Christian Ehrhardt <ehrhardt@...ux.vnet.ibm.com>,
	linux-mm@...ck.org, Nick Piggin <npiggin@...e.de>,
	Chris Mason <chris.mason@...cle.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] page-allocator: Under memory pressure, wait on
 pressure to relieve instead of congestion

On Tue, 9 Mar 2010, Mel Gorman wrote:

> Until it's timeout at least. It's still better than the current
> situation of sleeping on congestion.

Congestion may clear if memory becomes available in other zones.

> The ideal would be waiting on a per-node basis. I'm just not liking having
> to look up the node structure when freeing a patch of pages and making a
> cache line in there unnecessarily hot.

The node structure (pgdat) contains the zone structures. If you know the
type of zone then you can calculate the pgdat address.

> > But then an overallocated node may stall processes. If that node is full
> > of unreclaimable memory then the process may never wake up?
> Processes wake after a timeout.

Ok that limits it but still we may be waiting for no reason.

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