linux-kernel - Re: [PATCH] vmscan: initialize sc->nr

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Message-ID: <20090210221542.GA3672@cmpxchg.org>
Date:	Tue, 10 Feb 2009 23:15:42 +0100
From:	Johannes Weiner <hannes@...xchg.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	minchan.kim@...il.com, riel@...hat.com, wli@...ementarian.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] vmscan: initialize sc->nr_reclaimed properly take2

On Tue, Feb 10, 2009 at 02:06:37PM -0800, Andrew Morton wrote:
> On Tue, 10 Feb 2009 21:58:04 +0900 (JST)
> KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:
> 
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -1665,6 +1665,7 @@ unsigned long try_to_free_pages(struct z
> >  								gfp_t gfp_mask)
> >  {
> >  	struct scan_control sc = {
> > +		.nr_reclaimed = 0,
> >  		.gfp_mask = gfp_mask,
> >  		.may_writepage = !laptop_mode,
> >  		.swap_cluster_max = SWAP_CLUSTER_MAX,
> > @@ -1686,6 +1687,7 @@ unsigned long try_to_free_mem_cgroup_pag
> >  					   unsigned int swappiness)
> >  {
> >  	struct scan_control sc = {
> > +		.nr_reclaimed = 0,
> >  		.may_writepage = !laptop_mode,
> >  		.may_swap = 1,
> >  		.swap_cluster_max = SWAP_CLUSTER_MAX,
> > @@ -2245,6 +2247,7 @@ static int __zone_reclaim(struct zone *z
> >  	struct reclaim_state reclaim_state;
> >  	int priority;
> >  	struct scan_control sc = {
> > +		.nr_reclaimed = 0,
> >  		.may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
> >  		.may_swap = !!(zone_reclaim_mode & RECLAIM_SWAP),
> >  		.swap_cluster_max = max_t(unsigned long, nr_pages,
> 
> Confused.  The compiler already initialises any unmentioned fields to zero,
> so this patch has no effect.

Oh, nice, I was actually testing the wrong thing!

	struct foo foo;

wouldn't do that.  But

	struct foo foo = { .a = 5 };

actually would initialize foo.b = 0.

Sorry.  Please ignore this patch and the other one regarding the
explicit initialization of sc.order.  :(

	Hannes
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