linux-kernel - Re: [PATCH 02/19] mm/mpol: Remove NUMA_INTERLEAVE

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Date:	Thu, 9 Aug 2012 23:41:11 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	mingo@...nel.org, riel@...hat.com, oleg@...hat.com, pjt@...gle.com,
	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	tglx@...utronix.de, Lee.Schermerhorn@...com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/19] mm/mpol: Remove NUMA_INTERLEAVE_HIT

Hi,

On Tue, Jul 31, 2012 at 09:12:06PM +0200, Peter Zijlstra wrote:
> Since the NUMA_INTERLEAVE_HIT statistic is useless on its own; it wants
> to be compared to either a total of interleave allocations or to a miss
> count, remove it.
> 
> Fixing it would be possible, but since we've gone years without these
> statistics I figure we can continue that way.
> 
> Also NUMA_HIT fully includes NUMA_INTERLEAVE_HIT so users might
> switch to using that.
> 
> This cleans up some of the weird MPOL_INTERLEAVE allocation exceptions.

It's not apparent why you need to remove it for sched-numa. I think I
see it but it'd be nicer if it would explained so one doesn't need to
read an internal bit of several patches later to understand why this
is needed.

> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -169,7 +169,7 @@ static ssize_t node_read_numastat(struct
>  		       node_page_state(dev->id, NUMA_HIT),
>  		       node_page_state(dev->id, NUMA_MISS),
>  		       node_page_state(dev->id, NUMA_FOREIGN),
> -		       node_page_state(dev->id, NUMA_INTERLEAVE_HIT),
> +		       0UL,
>  		       node_page_state(dev->id, NUMA_LOCAL),
>  		       node_page_state(dev->id, NUMA_OTHER));
>  }

Not so nice to leave forever a 0 here. It doesn't matter if nobody can
act on it because it wants to be compared, it's still useful as an
informative value for vmstat below:

> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -717,7 +717,6 @@ const char * const vmstat_text[] = {
>  	"numa_hit",
>  	"numa_miss",
>  	"numa_foreign",
> -	"numa_interleave",
>  	"numa_local",
>  	"numa_other",
>  #endif
> 
> 
> --
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