linux-kernel - Re: [PATCH 4.3-rc6] proc: fix oom_adj value read from /proc/<pid>/oom

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Date:	Tue, 20 Oct 2015 12:27:58 -0500
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Hongjie Fang (方洪杰) 
	<Hongjie.Fang@...eadtrum.com>
Cc:	"gregkh\@linuxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, <linux-mm@...ck.org>
Subject: Re: [PATCH 4.3-rc6] proc: fix oom_adj value read from /proc/<pid>/oom_adj

"Hongjie Fang (方洪杰)" <Hongjie.Fang@...eadtrum.com> writes:

> The oom_adj's value reading through /proc/<pid>/oom_adj is different 
> with the value written into /proc/<pid>/oom_adj.
> Fix this by adding a adjustment factor.

*Scratches my head*

Won't changing the interpretation of what is written break existing
userspace applications that write this value?

Added a few more likely memory management suspects that might understand
what is going on here.

Eric

>
> Signed-off-by: Hongjie Fang <hongjie.fang@...eadtrum.com>
> ---
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index b25eee4..1ea0589 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -1043,6 +1043,7 @@ static ssize_t oom_adj_write(struct file *file, const char __user *buf,
>  	int oom_adj;
>  	unsigned long flags;
>  	int err;
> +	int adjust;
>  
>  	memset(buffer, 0, sizeof(buffer));
>  	if (count > sizeof(buffer) - 1)
> @@ -1084,8 +1085,10 @@ static ssize_t oom_adj_write(struct file *file, const char __user *buf,
>  	 */
>  	if (oom_adj == OOM_ADJUST_MAX)
>  		oom_adj = OOM_SCORE_ADJ_MAX;
> -	else
> -		oom_adj = (oom_adj * OOM_SCORE_ADJ_MAX) / -OOM_DISABLE;
> +	else{
> +		adjust = oom_adj > 0 ? (-OOM_DISABLE-1) : -(-OOM_DISABLE-1);
> +		oom_adj = (oom_adj * OOM_SCORE_ADJ_MAX + adjust) / -OOM_DISABLE;
> +	}
>  
>  	if (oom_adj < task->signal->oom_score_adj &&
>  	    !capable(CAP_SYS_RESOURCE)) {
>
> --
--
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