On Mon 25-06-12 18:47:53, David Rientjes wrote:
> The global oom killer is serialized by the zonelist being used in the
> page allocation. Concurrent oom kills are thus a rare event and only
> occur in systems using mempolicies and with a large number of nodes.
>
> Memory controller oom kills, however, can frequently be concurrent since
> there is no serialization once the oom killer is called for oom
> conditions in several different memcgs in parallel.
>
> This creates a massive contention on tasklist_lock since the oom killer
> requires the readside for the tasklist iteration. If several memcgs are
> calling the oom killer, this lock can be held for a substantial amount of
> time, especially if threads continue to enter it as other threads are
> exiting.
>
> Since the exit path grabs the writeside of the lock with irqs disabled in
> a few different places, this can cause a soft lockup on cpus as a result
> of tasklist_lock starvation.
>
> The kernel lacks unfair writelocks, and successful calls to the oom
> killer usually result in at least one thread entering the exit path, so
> an alternative solution is needed.
>
> This patch introduces a seperate oom handler for memcgs so that they do
> not require tasklist_lock for as much time. Instead, it iterates only
> over the threads attached to the oom memcg and grabs a reference to the
> selected thread before calling oom_kill_process() to ensure it doesn't
> prematurely exit.
>
> This still requires tasklist_lock for the tasklist dump, iterating
> children of the selected process, and killing all other threads on the
> system sharing the same memory as the selected victim. So while this
> isn't a complete solution to tasklist_lock starvation, it significantly
> reduces the amount of time that it is held.
There is an issues with memcg ref. counting but I like the approach in
general.
>
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
After the things bellow are fixed
Acked-by: Michal Hocko <mhocko@xxxxxxx>
> ---
> include/linux/memcontrol.h | 9 ++-----
> include/linux/oom.h | 16 ++++++++++++
> mm/memcontrol.c | 62 +++++++++++++++++++++++++++++++++++++++++++-
> mm/oom_kill.c | 48 +++++++++++-----------------------
> 4 files changed, 94 insertions(+), 41 deletions(-)
>
[...]
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
[...]
> @@ -1470,6 +1470,66 @@ u64 mem_cgroup_get_limit(struct mem_cgroup *memcg)
> return min(limit, memsw);
> }
>
> +void __mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
> + int order)
> +{
> + struct mem_cgroup *iter;
> + unsigned long chosen_points = 0;
> + unsigned long totalpages;
> + unsigned int points = 0;
> + struct task_struct *chosen = NULL;
> + struct task_struct *task;
> +
> + totalpages = mem_cgroup_get_limit(memcg) >> PAGE_SHIFT ? : 1;
> + for_each_mem_cgroup_tree(iter, memcg) {
> + struct cgroup *cgroup = iter->css.cgroup;
> + struct cgroup_iter it;
> +
> + cgroup_iter_start(cgroup, &it);
I guess this should protect from task move and exit, right?
> + while ((task = cgroup_iter_next(cgroup, &it))) {
> + switch (oom_scan_process_thread(task, totalpages, NULL,
> + false)) {
> + case OOM_SCAN_SELECT:
> + if (chosen)
> + put_task_struct(chosen);
> + chosen = task;
> + chosen_points = ULONG_MAX;
> + get_task_struct(chosen);
> + /* fall through */
> + case OOM_SCAN_CONTINUE:
> + continue;
> + case OOM_SCAN_ABORT:
> + cgroup_iter_end(cgroup, &it);
> + if (chosen)
> + put_task_struct(chosen);
You need mem_cgroup_iter_break here to have ref. counting correct.
> + return;
> + case OOM_SCAN_OK:
> + break;
> + };
> + points = oom_badness(task, memcg, NULL, totalpages);
> + if (points > chosen_points) {
> + if (chosen)
> + put_task_struct(chosen);
> + chosen = task;
> + chosen_points = points;
> + get_task_struct(chosen);
> + }
> + }
> + cgroup_iter_end(cgroup, &it);
> + if (!memcg->use_hierarchy)
> + break;
And this is not necessary, because for_each_mem_cgroup_tree is hierarchy
aware.
[...]
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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