linux-kernel - Re: mmotm 2015-01-22-15-04: qemu failure due to 'mm: memcontrol: remove unnecessary soft limit tree node test'

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Message-ID: <20150124071623.GA17705@phnom.home.cmpxchg.org>
Date:	Sat, 24 Jan 2015 02:16:23 -0500
From:	Johannes Weiner <hannes@...xchg.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Guenter Roeck <linux@...ck-us.net>, akpm@...ux-foundation.org,
	mm-commits@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	linux-next@...r.kernel.org, sfr@...b.auug.org.au, mhocko@...e.cz
Subject: Re: mmotm 2015-01-22-15-04: qemu failure due to 'mm: memcontrol:
 remove unnecessary soft limit tree node test'

On Fri, Jan 23, 2015 at 03:09:20PM -0600, Christoph Lameter wrote:
> On Fri, 23 Jan 2015, Guenter Roeck wrote:
> 
> > Wouldn't that have unintended consequences ? So far
> > rb tree nodes are allocated even if a node not online;
> > the above would change that. Are you saying it is
> > unnecessary to initialize rb tree nodes if the node
> > is not online ?
> 
> It is not advisable to allocate since an offline node means that the
> structure cannot be allocated on the node where it would be most
> beneficial. Typically subsystems allocate the per node data structures
> when the node is brought online.

I would generally agree, but this code, which implements a userspace
interface, is already grotesquely inefficient and heavyhanded.  It's
also superseded in the next release, so we can just keep this simple
at this point.
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