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

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Message-ID: <20160623084200.GA526@swordfish>
Date:	Thu, 23 Jun 2016 17:42:00 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Ganesh Mahendran <opensource.ganesh@...il.com>
Cc:	David Rientjes <rientjes@...gle.com>, devel@...verdev.osuosl.org,
	gregkh@...uxfoundation.org, arve@...roid.com,
	riandrews@...roid.com, linux-kernel@...r.kernel.org,
	sergey.senozhatsky.work@...il.com, sergey.senozhatsky@...il.com
Subject: Re: [PATCH 2/3] staging: lowmemorykiller: count anon pages only when
 we have swap devices

On (06/22/16 11:27), Ganesh Mahendran wrote:
[..]
> > > 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.

hm, looking at ->scan (lowmem_scan) shouldn't it return SHRINK_STOP
when it has nothing to free instead of 0?

	-ss