linux-kernel - Re: [patch 2/3] mm, oom: pass an oom order of -1 when triggered by sysrq

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Message-ID: <20150619073202.GD4913@dhcp22.suse.cz>
Date:	Fri, 19 Jun 2015 09:32:02 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [patch 2/3] mm, oom: pass an oom order of -1 when triggered by
 sysrq

On Thu 18-06-15 16:00:07, David Rientjes wrote:
> The force_kill member of struct oom_context isn't needed if an order of
> -1 is used instead.

But this doesn't make much sense to me. It is not like we would _have_
to spare few bytes here. The meaning of force_kill is clear while order
with a weird value is a hack. It is harder to follow without any good
reason.

> This patch introduces no functional change.
> 
> Signed-off-by: David Rientjes <rientjes@...gle.com>
> ---
>  drivers/tty/sysrq.c | 3 +--
>  include/linux/oom.h | 1 -
>  mm/memcontrol.c     | 1 -
>  mm/oom_kill.c       | 5 ++---
>  mm/page_alloc.c     | 1 -
>  5 files changed, 3 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
> --- a/drivers/tty/sysrq.c
> +++ b/drivers/tty/sysrq.c
> @@ -358,8 +358,7 @@ static void moom_callback(struct work_struct *ignored)
>  		.zonelist = node_zonelist(first_memory_node, gfp_mask),
>  		.nodemask = NULL,
>  		.gfp_mask = gfp_mask,
> -		.order = 0,
> -		.force_kill = true,
> +		.order = -1,
>  	};
>  
>  	mutex_lock(&oom_lock);
> diff --git a/include/linux/oom.h b/include/linux/oom.h
> --- a/include/linux/oom.h
> +++ b/include/linux/oom.h
> @@ -17,7 +17,6 @@ struct oom_control {
>  	nodemask_t	*nodemask;
>  	gfp_t		gfp_mask;
>  	int		order;
> -	bool		force_kill;
>  };
>  
>  /*
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1550,7 +1550,6 @@ static void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
>  		.nodemask = NULL,
>  		.gfp_mask = gfp_mask,
>  		.order = order,
> -		.force_kill = false,
>  	};
>  	struct mem_cgroup *iter;
>  	unsigned long chosen_points = 0;
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -265,7 +265,7 @@ enum oom_scan_t oom_scan_process_thread(struct oom_control *oc,
>  	 * Don't allow any other task to have access to the reserves.
>  	 */
>  	if (test_tsk_thread_flag(task, TIF_MEMDIE)) {
> -		if (!oc->force_kill)
> +		if (oc->order != -1)
>  			return OOM_SCAN_ABORT;
>  	}
>  	if (!task->mm)
> @@ -278,7 +278,7 @@ enum oom_scan_t oom_scan_process_thread(struct oom_control *oc,
>  	if (oom_task_origin(task))
>  		return OOM_SCAN_SELECT;
>  
> -	if (task_will_free_mem(task) && !oc->force_kill)
> +	if (task_will_free_mem(task) && oc->order != -1)
>  		return OOM_SCAN_ABORT;
>  
>  	return OOM_SCAN_OK;
> @@ -718,7 +718,6 @@ void pagefault_out_of_memory(void)
>  		.nodemask = NULL,
>  		.gfp_mask = 0,
>  		.order = 0,
> -		.force_kill = false,
>  	};
>  
>  	if (mem_cgroup_oom_synchronize(true))
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2685,7 +2685,6 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order,
>  		.nodemask = ac->nodemask,
>  		.gfp_mask = gfp_mask,
>  		.order = order,
> -		.force_kill = false,
>  	};
>  	struct page *page;
>  

-- 
Michal Hocko
SUSE Labs
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