linux-kernel - Re: [patch v2]numa: add a sysctl to control interleave allocation granularity from each node

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Message-ID: <alpine.DEB.2.00.1112061739140.27247@chino.kir.corp.google.com>
Date:	Tue, 6 Dec 2011 17:42:10 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Shaohua Li <shaohua.li@...el.com>
cc:	lkml <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	Jens Axboe <axboe@...nel.dk>, Christoph Lameter <cl@...ux.com>,
	"lee.schermerhorn@...com" <lee.schermerhorn@...com>
Subject: Re: [patch v2]numa: add a sysctl to control interleave allocation
 granularity from each node

On Wed, 7 Dec 2011, Shaohua Li wrote:

> based on the allocation size, right? I did consider it. It would be easy to
> implement this. Note even without my patch we have the issue if allocation
> from one node is big order and small order from other node. And nobody
> complains the imbalance. This makes me think maybe people didn't care
> about the imbalance too much.
> 

Right, I certainly see what you're trying to do and I support it, however, 
if we're going to add a userspace tunable then I think it would be better 
implemented as a size.  You can still get the functionality that you have 
with your patch (just with a size of 0, the default, making every 
allocation on the next node) but can also interleave on PAGE_SIZE, 
HPAGE_SIZE, etc, increments.  I think it would help for users who are 
concerned about node symmetry for contention on the memory bus and it 
would be a shame if someone needed to add a second tunable for that affect 
if your tunable already has applications using it.
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