linux-kernel - Re: [PATCH 08/31] mm, vmscan: simplify the logic deciding whether kswapd sleeps

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Date:	Tue, 5 Jul 2016 11:26:39 +0100
From:	Mel Gorman <mgorman@...hsingularity.net>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>, Rik van Riel <riel@...riel.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 08/31] mm, vmscan: simplify the logic deciding whether
 kswapd sleeps

On Tue, Jul 05, 2016 at 02:59:31PM +0900, Minchan Kim wrote:
> > @@ -3249,9 +3249,19 @@ static void kswapd_try_to_sleep(pg_data_t *pgdat, int order,
> >  
> >  	prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
> >  
> > +	/*
> > +	 * If kswapd has not been woken recently, then kswapd goes fully
> > +	 * to sleep. kcompactd may still need to wake if the original
> > +	 * request was high-order.
> > +	 */
> > +	if (classzone_idx == -1) {
> > +		wakeup_kcompactd(pgdat, alloc_order, classzone_idx);
> > +		classzone_idx = MAX_NR_ZONES - 1;
> > +		goto full_sleep;
> > +	}
> > +
> >  	/* Try to sleep for a short interval */
> > -	if (prepare_kswapd_sleep(pgdat, order, remaining,
> > -						balanced_classzone_idx)) {
> > +	if (prepare_kswapd_sleep(pgdat, reclaim_order, remaining, classzone_idx)) {
> 
> 
> Just trivial but this is clean up patch so I suggest one.
> If it doesn't help readability, just ignore, please.
> 
> This(ie, first prepare_kswapd_sleep always get 0 remaining value so
> it's pointless argument for the function. We could remove it and
> check it before second prepare_kswapd_sleep call.
> 

Yeah, fair point. I added a new patch that does this near the end of
the series with the other patches that avoid unnecessarily passing
parameters.

> > @@ -3418,10 +3426,10 @@ void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
> >  	if (!cpuset_zone_allowed(zone, GFP_KERNEL | __GFP_HARDWALL))
> >  		return;
> >  	pgdat = zone->zone_pgdat;
> > -	if (pgdat->kswapd_max_order < order) {
> > -		pgdat->kswapd_max_order = order;
> > -		pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx);
> > -	}
> > +	if (pgdat->kswapd_classzone_idx == -1)
> > +		pgdat->kswapd_classzone_idx = classzone_idx;
> 
> It's tricky. Couldn't we change kswapd_classzone_idx to integer type
> and remove if above if condition?
> 

It's tricky and not necessarily better overall. It's perfectly possible
to be woken up for zone index 0 so it's changing -1 to another magic
value.

-- 
Mel Gorman
SUSE Labs