Re: [patch v3] memcg: add oom killer delay

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Mon, 27 Dec 2010 22:29:05 -0800 (PST)
David Rientjes <rientjes@google.com> wrote:

> Completely disabling the oom killer for a memcg is problematic if
> userspace is unable to address the condition itself, usually because it
> is unresponsive.  This scenario creates a memcg deadlock: tasks are
> sitting in TASK_KILLABLE waiting for the limit to be increased, a task to
> exit or move, or the oom killer reenabled and userspace is unable to do
> so.
> 
> An additional possible use case is to defer oom killing within a memcg
> for a set period of time, probably to prevent unnecessary kills due to
> temporary memory spikes, before allowing the kernel to handle the
> condition.
> 
> This patch adds an oom killer delay so that a memcg may be configured to
> wait at least a pre-defined number of milliseconds before calling the oom
> killer.  If the oom condition persists for this number of milliseconds,
> the oom killer will be called the next time the memory controller
> attempts to charge a page (and memory.oom_control is set to 0).  This
> allows userspace to have a short period of time to respond to the
> condition before deferring to the kernel to kill a task.
> 
> Admins may set the oom killer delay using the new interface:
> 
> 	# echo 60000 > memory.oom_delay_millisecs
> 
> This will defer oom killing to the kernel only after 60 seconds has
> elapsed.  When setting memory.oom_delay, all pending delays have their
> charge retried and, if necessary, the new delay is then effected.
> 
> The delay is cleared the first time the memcg is oom to avoid unnecessary
> waiting when userspace is unresponsive for future oom conditions.  It may
> be set again using the above interface to enforce a delay on the next
> oom.
> 
> Signed-off-by: David Rientjes <rientjes@google.com>

Changelog please.


> ---
>  Documentation/cgroups/memory.txt |   26 +++++++++++++++++++++
>  mm/memcontrol.c                  |   46 ++++++++++++++++++++++++++++++++++---
>  2 files changed, 68 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
> index 7781857..e426733 100644
> --- a/Documentation/cgroups/memory.txt
> +++ b/Documentation/cgroups/memory.txt
> @@ -68,6 +68,7 @@ Brief summary of control files.
>  				 (See sysctl's vm.swappiness)
>   memory.move_charge_at_immigrate # set/show controls of moving charges
>   memory.oom_control		 # set/show oom controls.
> + memory.oom_delay_millisecs	 # set/show millisecs to wait before oom kill
>  
>  1. History
>  
> @@ -640,6 +641,31 @@ At reading, current status of OOM is shown.
>  	under_oom	 0 or 1 (if 1, the memory cgroup is under OOM, tasks may
>  				 be stopped.)
>  
> +It is also possible to configure an oom killer timeout to prevent the
> +possibility that the memcg will deadlock looking for memory if userspace
> +has disabled the oom killer with oom_control but cannot act to fix the
> +condition itself (usually because userspace has become unresponsive).
> +
> +To set an oom killer timeout for a memcg, write the number of milliseconds
> +to wait before killing a task to memory.oom_delay_millisecs:
> +
> +	# echo 60000 > memory.oom_delay_millisecs	# 60 seconds before kill
> +
> +This timeout is reset the first time the memcg is oom to prevent needlessly
> +waiting for the next oom when userspace is truly unresponsive.  It may be
> +set again using the above interface to defer killing a task the next time
> +the memcg is oom.
> +
> +Disabling the oom killer for a memcg with memory.oom_control takes
> +precedence over memory.oom_delay_millisecs, so it must be set to 0
> +(default) to allow the oom kill after the delay has expired.
> +
> +This value is inherited from the memcg's parent on creation.
> +
> +There is no delay if memory.oom_delay_millisecs is set to 0 (default).
> +This tunable's upper bound is 60 minutes.

Why upper-bounds is 60 minutes ? Do we have to have a limit ?
Hmm, I feel 60minutes is too short. I like 32 or 31 bit limit.


> +
> +
>  11. TODO
>  
>  1. Add support for accounting huge pages (as a separate controller)
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index e6aadd6..951a22c 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -229,6 +229,8 @@ struct mem_cgroup {
>  	unsigned int	swappiness;
>  	/* OOM-Killer disable */
>  	int		oom_kill_disable;
> +	/* number of ticks to stall before calling oom killer */
> +	int		oom_delay;
>  
>  	/* set when res.limit == memsw.limit */
>  	bool		memsw_is_minimum;
> @@ -1415,10 +1417,11 @@ static void memcg_oom_recover(struct mem_cgroup *mem)
>  /*
>   * try to call OOM killer. returns false if we should exit memory-reclaim loop.
>   */
> -bool mem_cgroup_handle_oom(struct mem_cgroup *mem, gfp_t mask)
> +static bool mem_cgroup_handle_oom(struct mem_cgroup *mem, gfp_t mask)
>  {
>  	struct oom_wait_info owait;
>  	bool locked, need_to_kill;
> +	long timeout = MAX_SCHEDULE_TIMEOUT;
>  
>  	owait.mem = mem;
>  	owait.wait.flags = 0;
> @@ -1437,15 +1440,21 @@ bool mem_cgroup_handle_oom(struct mem_cgroup *mem, gfp_t mask)
>  	prepare_to_wait(&memcg_oom_waitq, &owait.wait, TASK_KILLABLE);
>  	if (!locked || mem->oom_kill_disable)
>  		need_to_kill = false;
> -	if (locked)
> +	if (locked) {
> +		if (mem->oom_delay) {
> +			need_to_kill = false;
> +			timeout = mem->oom_delay;
> +			mem->oom_delay = 0;
> +		}
>  		mem_cgroup_oom_notify(mem);
> +	}
>  	mutex_unlock(&memcg_oom_mutex);
>  
>  	if (need_to_kill) {
>  		finish_wait(&memcg_oom_waitq, &owait.wait);
>  		mem_cgroup_out_of_memory(mem, mask);
>  	} else {
> -		schedule();
> +		schedule_timeout(timeout);
>  		finish_wait(&memcg_oom_waitq, &owait.wait);
>  	}
>  	mutex_lock(&memcg_oom_mutex);
> @@ -1456,7 +1465,8 @@ bool mem_cgroup_handle_oom(struct mem_cgroup *mem, gfp_t mask)
>  	if (test_thread_flag(TIF_MEMDIE) || fatal_signal_pending(current))
>  		return false;
>  	/* Give chance to dying process */
> -	schedule_timeout(1);
> +	if (timeout != MAX_SCHEDULE_TIMEOUT)

!= ?

This seems to change existing behavior.

> +		schedule_timeout(1);
>  	return true;
>  }
>  
> @@ -3863,6 +3873,28 @@ static int mem_cgroup_oom_control_write(struct cgroup *cgrp,
>  	return 0;
>  }
>  
> +static u64 mem_cgroup_oom_delay_millisecs_read(struct cgroup *cgrp,
> +					struct cftype *cft)
> +{
> +	struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
> +
> +	return jiffies_to_msecs(memcg->oom_delay);
> +}
> +
> +static int mem_cgroup_oom_delay_millisecs_write(struct cgroup *cgrp,
> +					struct cftype *cft, u64 val)
> +{
> +	struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
> +
> +	/* Sanity check -- don't wait longer than an hour */
> +	if (val > (60 * 60 * 1000))
> +		return -EINVAL;
> +
> +	memcg->oom_delay = msecs_to_jiffies(val);
> +	memcg_oom_recover(memcg);
> +	return 0;
> +}
> +

Please allow this to the root of sub-hierarchy and no children....(*)
(please check how mem_cgroup_oom_lock/unlock() works under use_hierarchy=1)

>  static struct cftype mem_cgroup_files[] = {
>  	{
>  		.name = "usage_in_bytes",
> @@ -3926,6 +3958,11 @@ static struct cftype mem_cgroup_files[] = {
>  		.unregister_event = mem_cgroup_oom_unregister_event,
>  		.private = MEMFILE_PRIVATE(_OOM_TYPE, OOM_CONTROL),
>  	},
> +	{
> +		.name = "oom_delay_millisecs",
> +		.read_u64 = mem_cgroup_oom_delay_millisecs_read,
> +		.write_u64 = mem_cgroup_oom_delay_millisecs_write,
> +	},
>  };
>  
>  #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
> @@ -4164,6 +4201,7 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
>  		parent = mem_cgroup_from_cont(cont->parent);
>  		mem->use_hierarchy = parent->use_hierarchy;
>  		mem->oom_kill_disable = parent->oom_kill_disable;
> +		mem->oom_delay = parent->oom_delay;

Becasue of (*), oom_kill_disable can be copied here.
If you want to inherit this, you should do (*) or update all hierarchy value.


Thanks,
-Kame

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