linux-kernel - Re: [PATCH 2/4] slqb: Record what node is local to a kmem_cache

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Date:	Mon, 5 Oct 2009 10:49:04 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	Christoph Lameter <cl@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>, heiko.carstens@...ibm.com,
	sachinp@...ibm.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Tejun Heo <tj@...nel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH 2/4] slqb: Record what node is local to a kmem_cache_cpu

On Sun, Oct 04, 2009 at 03:06:45PM +0300, Pekka Enberg wrote:
> On Thu, Oct 1, 2009 at 2:45 AM, Christoph Lameter
> <cl@...ux-foundation.org> wrote:
> >> This is essentially the "unqueued" nature of SLUB. It's objective "I have this
> >> page here which I'm going to use until I can't use it no more and will depend
> >> on the page allocator to sort my stuff out". I have to read up on SLUB up
> >> more to see if it's compatible with SLQB or not though. In particular, how
> >> does SLUB deal with frees from pages that are not the "current" page? SLQB
> >> does not care what page the object belongs to as long as it's node-local
> >> as the object is just shoved onto a LIFO for maximum hotness.
> >
> > Frees are done directly to the target slab page if they are not to the
> > current active slab page. No centralized locks. Concurrent frees from
> > processors on the same node to multiple other nodes (or different pages
> > on the same node) can occur.
> >
> >> > SLAB deals with it in fallback_alloc(). It scans the nodes in zonelist
> >> > order for free objects of the kmem_cache and then picks up from the
> >> > nearest node. Ugly but it works. SLQB would have to do something similar
> >> > since it also has the per node object bins that SLAB has.
> >> >
> >>
> >> In a real sense, this is what the patch ends up doing. When it fails to
> >> get something locally but sees that the local node is memoryless, it
> >> will check the remote node lists in zonelist order. I think that's
> >> reasonable behaviour but I'm biased because I just want the damn machine
> >> to boot again. What do you think? Pekka, Nick?
> >
> > Look at fallback_alloc() in slab. You can likely copy much of it. It
> > considers memory policies and cpuset constraints.
> 
> Sorry for the delay. I went ahead and merged Mel's patch to make
> things boot on PPC. Fallback policy needs a bit more work as Christoph
> says but I'd really love to have Nick's input on this.
> 
> Mel, do you have a Kconfig patch laying around somewhere to enable
> SLQB on PPC and S390?
> 

It's patch 4 of this series.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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