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

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Date:	Tue, 21 Jun 2016 13:22:00 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Ganesh Mahendran <opensource.ganesh@...il.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

On Tue, 21 Jun 2016, Ganesh Mahendran wrote:

> lowmem_count() should only count anon pages when we have swap device.
> 

Why?

> 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.