linux-kernel - Re: [PATCH] Don't touch single threaded PTEs which are on the right node

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Date:   Thu, 13 Oct 2016 19:16:37 +0100
From:   Mel Gorman <mgorman@...e.de>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Andi Kleen <andi@...stfloor.org>, peterz@...radead.org,
        linux-mm@...ck.org, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Don't touch single threaded PTEs which are on the right
 node

On Thu, Oct 13, 2016 at 11:04:02AM -0700, Andi Kleen wrote:
> > >  	do {
> > >  		oldpte = *pte;
> > > @@ -94,6 +100,13 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
> > >  				/* Avoid TLB flush if possible */
> > >  				if (pte_protnone(oldpte))
> > >  					continue;
> > > +
> > > +				/*
> > > +				 * Don't mess with PTEs if page is already on the node
> > > +				 * a single-threaded process is running on.
> > > +				 */
> > > +				if (target_node == page_to_nid(page))
> > > +					continue;
> > >  			}
> > >  
> > 
> > Check target_node != NUMA_NODE && target_node == page_to_nid(page) to
> > avoid unnecessary page->flag masking and shifts?
> 
> I didn't do this last change because I expect a potentially mispredicted
> check is more expensive than some shifting/masking.
> 

Ok, that's fair enough. For something that minor I expect it to be a
case of "you win some you lose some" depending on workload, CPU and
phase of the moon.

Thanks.

-- 
Mel Gorman
SUSE Labs