linux-kernel - Re: [PATCH 5/8] sched, numa, mm: Add adaptive NUMA affinity support

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Message-ID: <m2sj7sfbk8.fsf@firstfloor.org>
Date:	Thu, 29 Nov 2012 11:34:15 -0800
From:	Andi Kleen <andi@...stfloor.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Paul Turner <pjt@...gle.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Christoph Lameter <cl@...ux.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 5/8] sched, numa, mm: Add adaptive NUMA affinity support

Peter Zijlstra <a.p.zijlstra@...llo.nl> writes:

> +
> +		down_write(&mm->mmap_sem);
> +		for (vma = mm->mmap; vma; vma = vma->vm_next) {
> +			if (!vma_migratable(vma))
> +				continue;
> +			change_protection(vma, vma->vm_start, vma->vm_end, vma_prot_none(vma), 0);
> +		}

What happens if I have a 1TB process? Will you really unmap all of the
1TB in that timer?


>  
>  	case MPOL_PREFERRED:
>  		if (pol->flags & MPOL_F_LOCAL)
> -			polnid = numa_node_id();
> +			best_nid = numa_node_id();
>  		else
> -			polnid = pol->v.preferred_node;
> +			best_nid = pol->v.preferred_node;

So that's not the local node anymore?  That will change behaviour for
people using the NUMA affinity APIs explicitely.  I don't think that's a
good idea, if someone set the affinity explicitely the kernel better
follow that.

If you want to change behaviour for non DEFAULT like this
please use a new policy type.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only
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