linux-kernel - Re: [PATCH 14/35] autonuma: knuma

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Date:	Wed, 30 May 2012 02:14:38 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Hillf Danton <dhillf@...il.com>, Dan Smith <danms@...ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Paul Turner <pjt@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Mike Galbraith <efault@....de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Bharata B Rao <bharata.rao@...il.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH 14/35] autonuma: knuma_migrated per NUMA node queues

Hi,

On Tue, May 29, 2012 at 03:51:08PM +0200, Peter Zijlstra wrote:
> On Fri, 2012-05-25 at 19:02 +0200, Andrea Arcangeli wrote:
> 
> 
> > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> > index 41aa49b..8e578e6 100644
> > --- a/include/linux/mmzone.h
> > +++ b/include/linux/mmzone.h
> > @@ -666,6 +666,12 @@ typedef struct pglist_data {
> >  	struct task_struct *kswapd;
> >  	int kswapd_max_order;
> >  	enum zone_type classzone_idx;
> > +#ifdef CONFIG_AUTONUMA
> > +	spinlock_t autonuma_lock;
> > +	struct list_head autonuma_migrate_head[MAX_NUMNODES];
> > +	unsigned long autonuma_nr_migrate_pages;
> > +	wait_queue_head_t autonuma_knuma_migrated_wait;
> > +#endif
> >  } pg_data_t;
> >  
> >  #define node_present_pages(nid)	(NODE_DATA(nid)->node_present_pages)
> 
> O(nr_nodes^2) data.. ISTR people rewriting a certain slab allocator to
> get rid of that :-)
> 
> Also, don't forget that MAX_NUMNODES is an unconditional 512 on distro
> kernels, even when we only have 2.
> 
> Now the total wasted space isn't too bad since its only 16 bytes,
> totaling a whole 2M for a 256 node system. But still, something like
> that wants at least a mention somewhere.

I fully agree, I prefer to fix it and I was fully aware about
this. It's not a big deal so it got low priority to be fixed, but I
intended to optimize this.

As long as num_possible_nodes() is initialized before the pgdat is
allocated it shouldn't be difficult to optimize this moving struct
list_head autonuma_migrate_head[0] at the end of the structure.

mm_autonuma and sched_autonuma initially also had MAX_NUMNODES arrays
in them, then I converted to dynamic allocations to be optimal. We
same needs to happen here. 

Thanks,
Andrea
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