linux-kernel - Re: [PATCH] oom_reaper: switch to struct list

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Message-ID: <20170214163005.GA2450@cmpxchg.org>
Date:   Tue, 14 Feb 2017 11:30:05 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     Aleksa Sarai <asarai@...e.de>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, cyphar@...har.com
Subject: Re: [PATCH] oom_reaper: switch to struct list_head for reap queue

On Wed, Feb 15, 2017 at 02:07:14AM +1100, Aleksa Sarai wrote:
> Rather than implementing an open addressing linked list structure
> ourselves, use the standard list_head structure to improve consistency
> with the rest of the kernel and reduce confusion.
> 
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Signed-off-by: Aleksa Sarai <asarai@...e.de>
> ---
>  include/linux/sched.h |  6 +++++-
>  kernel/fork.c         |  4 ++++
>  mm/oom_kill.c         | 24 +++++++++++++-----------
>  3 files changed, 22 insertions(+), 12 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index e93594b88130..d8bcd0f8c5fe 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1960,7 +1960,11 @@ struct task_struct {
>  #endif
>  	int pagefault_disabled;
>  #ifdef CONFIG_MMU
> -	struct task_struct *oom_reaper_list;
> +	/*
> +	 * List of threads that have to be reaped by OOM (rooted at
> +	 * &oom_reaper_list in mm/oom_kill.c).
> +	 */
> +	struct list_head oom_reaper_list;

This is an extra pointer to task_struct and more lines of code to
accomplish the same thing. Why would we want to do that?