linux-kernel - Re: [PATCH v4] zone_reclaim is always 0 by default

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Date:	Thu, 4 Jun 2009 07:24:09 -0500
From:	Robin Holt <holt@....com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Christoph Lameter <cl@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, Robin Holt <holt@....com>,
	"Zhang, Yanmin" <yanmin.zhang@...el.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	linux-ia64@...r.kernel.org, linuxppc-dev@...abs.org,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v4] zone_reclaim is always 0 by default

Acked-by: Robin Holt <holt@....com>


On Thu, Jun 04, 2009 at 07:23:15PM +0900, KOSAKI Motohiro wrote:
...
> Actually, zone_reclaim_mode=1 mean "I dislike remote node allocation rather than
> disk access", it makes performance improvement to HPC workload.
> but it makes performance degression to desktop, file server and web server.

I still disagree with this statement, but I don't care that much.
Why not something more to the effect of:

Setting zone_reclaim_mode=1 causes memory allocations on a nearly
exhausted node to do direct reclaim within that node before attempting
off-node allocations.  For work loads where most pages are clean in
page cache and easily reclaimed, this can result excessive disk activity
versus a more fair node memory balance.

If you disagree, don't respond, just ignore.

...
> --- a/include/linux/topology.h
> +++ b/include/linux/topology.h
> @@ -54,12 +54,7 @@ int arch_update_cpu_topology(void);
>  #define node_distance(from,to)	((from) == (to) ? LOCAL_DISTANCE : REMOTE_DISTANCE)
>  #endif
>  #ifndef RECLAIM_DISTANCE
> -/*
> - * If the distance between nodes in a system is larger than RECLAIM_DISTANCE
> - * (in whatever arch specific measurement units returned by node_distance())
> - * then switch on zone reclaim on boot.
> - */
> -#define RECLAIM_DISTANCE 20
> +#define RECLAIM_DISTANCE INT_MAX

Why remove this comment?  It seems more-or-less a reasonable statement.

Thanks,
Robin
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