linux-kernel - Re: [PATCH 4/8] sched: Update NUMA hinting faults once per scan

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Message-ID: <20130628090159.GC28407@twins.programming.kicks-ass.net>
Date:	Fri, 28 Jun 2013 11:01:59 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Mel Gorman <mgorman@...e.de>, Ingo Molnar <mingo@...nel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/8] sched: Update NUMA hinting faults once per scan

On Fri, Jun 28, 2013 at 12:02:33PM +0530, Srikar Dronamraju wrote:
> * Mel Gorman <mgorman@...e.de> [2013-06-26 15:38:03]:
> > @@ -831,9 +837,13 @@ void task_numa_fault(int node, int pages, bool migrated)
> >  	if (unlikely(!p->numa_faults)) {
> >  		int size = sizeof(*p->numa_faults) * nr_node_ids;
> >  
> > -		p->numa_faults = kzalloc(size, GFP_KERNEL);
> > +		/* numa_faults and numa_faults_buffer share the allocation */
> > +		p->numa_faults = kzalloc(size * 2, GFP_KERNEL);
> 
> Instead of allocating buffer to hold the current faults, cant we pass
> the nr of pages and node information (and probably migrate) to
> task_numa_placement()?.

I'm afraid I don't get your question; there's more storage required than
just the arguments.

> Why should task_struct be passed as an argument to  task_numa_placement().
> It seems it always will be current.

Customary for parts -- motivated by the fact that usage of current
is/can be more expensive than passing an argument.
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