linux-kernel - Re: [PATCH 5/6] mm: kswapd: Treat zone->all_unreclaimable in sleeping_prematurely similar to balance

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Date:	Mon, 13 Dec 2010 08:58:55 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Simon Kirby <sim@...tway.ca>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Shaohua Li <shaohua.li@...el.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/6] mm: kswapd: Treat zone->all_unreclaimable in
 sleeping_prematurely similar to balance_pgdat()

On Fri, 10 Dec 2010 10:55:32 +0000
Mel Gorman <mel@....ul.ie> wrote:

> On Fri, Dec 10, 2010 at 10:23:37AM +0900, KAMEZAWA Hiroyuki wrote:
> > On Thu,  9 Dec 2010 11:18:19 +0000
> > Mel Gorman <mel@....ul.ie> wrote:
> > 
> > > After DEF_PRIORITY, balance_pgdat() considers all_unreclaimable zones to
> > > be balanced but sleeping_prematurely does not. This can force kswapd to
> > > stay awake longer than it should. This patch fixes it.
> > > 
> > > Signed-off-by: Mel Gorman <mel@....ul.ie>
> > 
> > Hmm, maybe the logic works well but I don't like very much.
> > 
> > How about adding below instead of pgdat->node_present_pages ?
> > 
> > static unsigned long required_balanced_pages(pgdat, classzone_idx)
> > {
> > 	unsigned long present = 0;
> > 
> > 	for_each_zone_in_node(zone, pgdat) {
> > 		if (zone->all_unreclaimable) /* Ignore unreclaimable zone at checking balance */
> > 			continue;
> > 		if (zone_idx(zone) > classzone_idx)
> > 			continue;
> > 		present = zone->present_pages;
> > 	}
> > 	return present;
> > }
> > 
> 
> I'm afraid I do not really understand. After your earlier comments,
> pgdat_balanced() now looks like
> 
> static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced_pages,
>                                                 int classzone_idx)
> {
>         unsigned long present_pages = 0;
>         int i;
> 
>         for (i = 0; i <= classzone_idx; i++)
>                 present_pages += pgdat->node_zones[i].present_pages;
> 
>         return balanced_pages > (present_pages >> 2);
> }
> 
> so the classzone is being taken into account. I'm not sure what you're
> asking for it to be changed to. Maybe it'll be clearer after V4 comes
> out rebased on top of mmotm.
> 

Ah, this seems okay to me.

Thank you.
-Kame



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