linux-kernel - Re: [PATCH 2/3] staging: lowmemorykiller: count anon pages only when we have swap devices

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Date:	Wed, 22 Jun 2016 11:27:51 +0800
From:	Ganesh Mahendran <opensource.ganesh@...il.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
	gregkh@...uxfoundation.org, arve@...roid.com, riandrews@...roid.com
Subject: Re: [PATCH 2/3] staging: lowmemorykiller: count anon pages only when
 we have swap devices

Hi, David:

On Tue, Jun 21, 2016 at 01:22:00PM -0700, David Rientjes wrote:
> On Tue, 21 Jun 2016, Ganesh Mahendran wrote:
> 
> > lowmem_count() should only count anon pages when we have swap device.
> > 
> 
> Why?

I make a mistake. I thought lowmem_count will return the shrinkalbe page
of a process.

> 
> > Signed-off-by: Ganesh Mahendran <opensource.ganesh@...il.com>
> > ---
> >  drivers/staging/android/lowmemorykiller.c | 12 ++++++++----
> >  1 file changed, 8 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/staging/android/lowmemorykiller.c b/drivers/staging/android/lowmemorykiller.c
> > index 6da9260..1d8de47 100644
> > --- a/drivers/staging/android/lowmemorykiller.c
> > +++ b/drivers/staging/android/lowmemorykiller.c
> > @@ -73,10 +73,14 @@ static unsigned long lowmem_deathpending_timeout;
> >  static unsigned long lowmem_count(struct shrinker *s,
> >  				  struct shrink_control *sc)
> >  {
> > -	return global_page_state(NR_ACTIVE_ANON) +
> > -		global_page_state(NR_ACTIVE_FILE) +
> > -		global_page_state(NR_INACTIVE_ANON) +
> > -		global_page_state(NR_INACTIVE_FILE);
> > +	unsigned long freeable = global_page_state(NR_ACTIVE_FILE) +
> > +				global_page_state(NR_INACTIVE_FILE);
> > +
> > +	if (get_nr_swap_pages() > 0)
> > +		freeable += global_page_state(NR_ACTIVE_ANON) +
> > +				global_page_state(NR_INACTIVE_ANON);
> > +
> > +	return freeable;
> >  }
> >  
> >  static unsigned long lowmem_scan(struct shrinker *s, struct shrink_control *sc)
> 
> Shouldn't this be advertising the amount of memory that is freeable by 
> killing the process with the highest priority oom_score_adj?  It's not 
> legitimate to say it can free all anon and file memory if nothing is oom 
> killable, so this function is wrong both originally and with your patched 
> version.

Yes, so should we just simply return 1 to make do_shrink_slab() go ahead?
Then lowmem_scan() will do the real job to scan all the process.

Thanks.