linux-kernel - Re: [patch 7/7 -mm] oom: remove unnecessary code and cleanup

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Message-Id: <20100212091237.adb94384.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 12 Feb 2010 09:12:37 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Nick Piggin <npiggin@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Lubos Lunak <l.lunak@...e.cz>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [patch 7/7 -mm] oom: remove unnecessary code and cleanup

On Wed, 10 Feb 2010 08:32:24 -0800 (PST)
David Rientjes <rientjes@...gle.com> wrote:

> Remove the redundancy in __oom_kill_task() since:
> 
>  - init can never be passed to this function: it will never be PF_EXITING
>    or selectable from select_bad_process(), and
> 
>  - it will never be passed a task from oom_kill_task() without an ->mm
>    and we're unconcerned about detachment from exiting tasks, there's no
>    reason to protect them against SIGKILL or access to memory reserves.
> 
> Also moves the kernel log message to a higher level since the verbosity
> is not always emitted here; we need not print an error message if an
> exiting task is given a longer timeslice.
> 
> Signed-off-by: David Rientjes <rientjes@...gle.com>

If you say "never", it's better to add BUG_ON() rather than 
if (!p->mm)...

But yes, this patch seesm to remove unnecessary codes.
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>


> ---
>  mm/oom_kill.c |   64 ++++++++++++++------------------------------------------
>  1 files changed, 16 insertions(+), 48 deletions(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -400,67 +400,35 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
>  		dump_tasks(mem);
>  }
>  
> -#define K(x) ((x) << (PAGE_SHIFT-10))
> -
>  /*
> - * Send SIGKILL to the selected  process irrespective of  CAP_SYS_RAW_IO
> - * flag though it's unlikely that  we select a process with CAP_SYS_RAW_IO
> - * set.
> + * Give the oom killed task high priority and access to memory reserves so that
> + * it may quickly exit and free its memory.
>   */
> -static void __oom_kill_task(struct task_struct *p, int verbose)
> +static void __oom_kill_task(struct task_struct *p)
>  {
> -	if (is_global_init(p)) {
> -		WARN_ON(1);
> -		printk(KERN_WARNING "tried to kill init!\n");
> -		return;
> -	}
> -
> -	task_lock(p);
> -	if (!p->mm) {
> -		WARN_ON(1);
> -		printk(KERN_WARNING "tried to kill an mm-less task %d (%s)!\n",
> -			task_pid_nr(p), p->comm);
> -		task_unlock(p);
> -		return;
> -	}
> -
> -	if (verbose)
> -		printk(KERN_ERR "Killed process %d (%s) "
> -		       "vsz:%lukB, anon-rss:%lukB, file-rss:%lukB\n",
> -		       task_pid_nr(p), p->comm,
> -		       K(p->mm->total_vm),
> -		       K(get_mm_counter(p->mm, MM_ANONPAGES)),
> -		       K(get_mm_counter(p->mm, MM_FILEPAGES)));
> -	task_unlock(p);
> -
> -	/*
> -	 * We give our sacrificial lamb high priority and access to
> -	 * all the memory it needs. That way it should be able to
> -	 * exit() and clear out its resources quickly...
> -	 */
>  	p->rt.time_slice = HZ;
>  	set_tsk_thread_flag(p, TIF_MEMDIE);
> -
>  	force_sig(SIGKILL, p);
>  }
>  
> +#define K(x) ((x) << (PAGE_SHIFT-10))
>  static int oom_kill_task(struct task_struct *p)
>  {
> -	/* WARNING: mm may not be dereferenced since we did not obtain its
> -	 * value from get_task_mm(p).  This is OK since all we need to do is
> -	 * compare mm to q->mm below.
> -	 *
> -	 * Furthermore, even if mm contains a non-NULL value, p->mm may
> -	 * change to NULL at any time since we do not hold task_lock(p).
> -	 * However, this is of no concern to us.
> -	 */
> -	if (!p->mm || p->signal->oom_adj == OOM_DISABLE)
> +	task_lock(p);
> +	if (!p->mm || p->signal->oom_adj == OOM_DISABLE) {
> +		task_unlock(p);
>  		return 1;
> +	}
> +	pr_err("Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB\n",
> +		task_pid_nr(p), p->comm, K(p->mm->total_vm),
> +	       K(get_mm_counter(p->mm, MM_ANONPAGES)),
> +	       K(get_mm_counter(p->mm, MM_FILEPAGES)));
> +	task_unlock(p);
>  
> -	__oom_kill_task(p, 1);
> -
> +	__oom_kill_task(p);
>  	return 0;
>  }
> +#undef K
>  
>  static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
>  			    unsigned int points, unsigned long totalpages,
> @@ -479,7 +447,7 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
>  	 * its children or threads, just set TIF_MEMDIE so it can die quickly
>  	 */
>  	if (p->flags & PF_EXITING) {
> -		__oom_kill_task(p, 0);
> +		__oom_kill_task(p);
>  		return 0;
>  	}
>  
> 

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