linux-kernel - Re: [RFC]numa: improve I/O performance by optimizing numa interleave allocation

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Message-ID: <alpine.DEB.2.00.1111180954200.2242@router.home>
Date:	Fri, 18 Nov 2011 09:56:15 -0600 (CST)
From:	Christoph Lameter <cl@...ux.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,
	Jens Axboe <axboe@...nel.dk>, lee.schermerhorn@...com
Subject: Re: [RFC]numa: improve I/O performance by optimizing numa interleave
 allocation

On Fri, 18 Nov 2011, Shaohua Li wrote:

> So can we make both interleave fairness and continuous allocation happy?

Maybe.

> Simplily we can adjust the round robin algorithm. We switch to another node
> after several (N) allocation happens. If N isn't too big, we can still get
> fair allocation. And we get N continuous pages. I use N=8 in below patch.
> I thought 8 isn't too big for modern NUMA machine. Applications which use
> interleave are unlikely run short time, so I thought fairness still works.

People are already complaining that the 4k interleaving is too coarse.
Bioses can often interleave on a cacheline level. A smaller size balances
the load better over multiple nodes. Large sizes can result in imbalances
since f.e. a whole array may end up on one node. Maybe make it tunable
by expanding the numa_policy structure to include a size parameter?


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