On Wed, 9 Feb 2011 14:19:50 -0800 (PST)
David Rientjes <rientjes@xxxxxxxxxx> 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 by putting the task to sleep for 60 seconds. When setting
> memory.oom_delay_millisecs, all pending delays have their charges retried
> and, if necessary, the new delay is then enforced.
>
> 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.
>
> When a memory.oom_delay_millisecs is set for a cgroup, it is propagated
> to all children memcg as well and is inherited when a new memcg is
> created.
>
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Hm. But I'm not sure how this will be used.
> ---
> Documentation/cgroups/memory.txt | 32 +++++++++++++++++++++++++
> mm/memcontrol.c | 48 ++++++++++++++++++++++++++++++++++---
> 2 files changed, 76 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
> --- 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 +641,37 @@ 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
> +
> +When this memcg is oom, it is guaranteed that this delay will be incurred
> +before the kernel kills a task. The task chosen may either be from this
> +memcg or its child memcgs, if any.
> +
> +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. Setting a
> +delay for a memcg sets the same delay for all children, as well.
> +
> +There is no delay if memory.oom_delay_millisecs is set to 0 (default).
> +This tunable's upper bound is MAX_SCHEDULE_TIMEOUT (about 24 days on
> +32-bit and a lifetime on 64-bit).
> +
> +
> 11. TODO
>
> 1. Add support for accounting huge pages (as a separate controller)
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -239,6 +239,8 @@ 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;
> @@ -1541,10 +1543,11 @@ 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;
> @@ -1563,15 +1566,21 @@ 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);
> @@ -1582,7 +1591,8 @@ 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)
> + schedule_timeout(1);
> return true;
> }
>
> @@ -4168,6 +4178,30 @@ 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);
> + struct mem_cgroup *iter;
> +
> + if (val > MAX_SCHEDULE_TIMEOUT)
> + return -EINVAL;
> +
> + for_each_mem_cgroup_tree(iter, memcg) {
> + iter->oom_delay = msecs_to_jiffies(val);
> + memcg_oom_recover(iter);
> + }
> + return 0;
> +}
> +
> static struct cftype mem_cgroup_files[] = {
> {
> .name = "usage_in_bytes",
> @@ -4231,6 +4265,11 @@ 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
> @@ -4469,6 +4508,7 @@ 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;
> }
>
> if (parent && parent->use_hierarchy) {
>
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