linux-kernel - Re: Free memory never fully used, swapping

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Date:	Tue, 30 Nov 2010 01:13:25 -0800
From:	Simon Kirby <sim@...tway.ca>
To:	Christoph Lameter <cl@...ux.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mel Gorman <mel@....ul.ie>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: Free memory never fully used, swapping

On Fri, Nov 26, 2010 at 09:48:14AM -0600, Christoph Lameter wrote:

> On Thu, 25 Nov 2010, KOSAKI Motohiro wrote:
> > Please try SLAB instead SLUB (it can be switched by kernel build option).
> > SLUB try to use high order allocation implicitly.
> 
> SLAB uses orders 0-1. Order is fixed per slab cache and determined based
> on object size at slab creation.
> 
> SLUB uses orders 0-3. Falls back to smallest order if alloc order cannot
> be met by the page allocator.
> 
> One can reduce SLUB to SLAB orders by specifying the following kernel
> commandline parameter:
> 
> slub_max_order=1

Can we also mess with these /sys files on the fly?

[/sys/kernel/slab]# grep . kmalloc-*/order | sort -n -k2 -t-
kmalloc-8/order:0
kmalloc-16/order:0
kmalloc-32/order:0
kmalloc-64/order:0
kmalloc-96/order:0
kmalloc-128/order:0
kmalloc-192/order:0
kmalloc-256/order:1
kmalloc-512/order:2
kmalloc-1024/order:3
kmalloc-2048/order:3
kmalloc-4096/order:3
kmalloc-8192/order:3

I'm not familiar with how slub works, but I assume there's some overhead
or some reason not to just use order 0 for <= kmalloc-4096?  Or is it
purely just trying to reduce cpu by calling alloc_pages less often?

Simon-
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