> This removes the check for a parallel memcg oom killing since we can
> guarantee that's not going to happen if we take ZONE_OOM_LOCKED for all
> populated zones (nobody is currently executing the oom killer) and no
> tasks have TIF_MEMDIE set.
>
> Signed-off-by: David Rientjes <rientjes@google.com>
> ---
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -124,7 +124,6 @@ static inline bool mem_cgroup_disabled(void)
> return false;
> }
>
> -extern bool mem_cgroup_oom_called(struct task_struct *task);
> void mem_cgroup_update_file_mapped(struct page *page, int val);
> unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
> gfp_t gfp_mask, int nid,
> @@ -258,11 +257,6 @@ static inline bool mem_cgroup_disabled(void)
> return true;
> }
>
> -static inline bool mem_cgroup_oom_called(struct task_struct *task)
> -{
> - return false;
> -}
> -
> static inline int
> mem_cgroup_inactive_anon_is_low(struct mem_cgroup *memcg)
> {
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -200,7 +200,6 @@ struct mem_cgroup {
> * Should the accounting and control be hierarchical, per subtree?
> */
> bool use_hierarchy;
> - unsigned long last_oom_jiffies;
> atomic_t refcnt;
>
> unsigned int swappiness;
> @@ -1234,34 +1233,6 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
> return total;
> }
>
> -bool mem_cgroup_oom_called(struct task_struct *task)
> -{
> - bool ret = false;
> - struct mem_cgroup *mem;
> - struct mm_struct *mm;
> -
> - rcu_read_lock();
> - mm = task->mm;
> - if (!mm)
> - mm = &init_mm;
> - mem = mem_cgroup_from_task(rcu_dereference(mm->owner));
> - if (mem && time_before(jiffies, mem->last_oom_jiffies + HZ/10))
> - ret = true;
> - rcu_read_unlock();
> - return ret;
> -}
> -
> -static int record_last_oom_cb(struct mem_cgroup *mem, void *data)
> -{
> - mem->last_oom_jiffies = jiffies;
> - return 0;
> -}
> -
> -static void record_last_oom(struct mem_cgroup *mem)
> -{
> - mem_cgroup_walk_tree(mem, NULL, record_last_oom_cb);
> -}
> -
> /*
> * Currently used to update mapped file statistics, but the routine can be
> * generalized to update other statistics as well.
> @@ -1549,10 +1520,8 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
> }
>
> if (!nr_retries--) {
> - if (oom) {
> + if (oom)
> mem_cgroup_out_of_memory(mem_over_limit, gfp_mask);
> - record_last_oom(mem_over_limit);
> - }
> goto nomem;
> }
> }
> @@ -2408,8 +2377,6 @@ void mem_cgroup_end_migration(struct mem_cgroup *mem,
>
> /*
> * A call to try to shrink memory usage on charge failure at shmem's swapin.
> - * Calling hierarchical_reclaim is not enough because we should update
> - * last_oom_jiffies to prevent pagefault_out_of_memory from invoking global OOM.
> * Moreover considering hierarchy, we should reclaim from the mem_over_limit,
> * not from the memcg which this page would be charged to.
> * try_charge_swapin does all of these works properly.
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -490,29 +490,6 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
> return oom_kill_task(victim);
> }
>
> -#ifdef CONFIG_CGROUP_MEM_RES_CTLR
> -void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask)
> -{
> - unsigned long points = 0;
> - struct task_struct *p;
> -
> - read_lock(&tasklist_lock);
> -retry:
> - p = select_bad_process(&points, mem, CONSTRAINT_NONE, NULL);
> - if (PTR_ERR(p) == -1UL)
> - goto out;
> -
> - if (!p)
> - p = current;
> -
> - if (oom_kill_process(p, gfp_mask, 0, points, mem,
> - "Memory cgroup out of memory"))
> - goto retry;
> -out:
> - read_unlock(&tasklist_lock);
> -}
> -#endif
> -
> static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
>
> int register_oom_notifier(struct notifier_block *nb)
> @@ -578,6 +555,70 @@ void clear_zonelist_oom(struct zonelist *zonelist, gfp_t gfp_mask)
> }
>
> /*
> + * Try to acquire the oom killer lock for all system zones. Returns zero if a
> + * parallel oom killing is taking place, otherwise locks all zones and returns
> + * non-zero.
> + */
> +static int try_set_system_oom(void)
> +{
> + struct zone *zone;
> + int ret = 1;
> +
> + spin_lock(&zone_scan_lock);
> + for_each_populated_zone(zone)
> + if (zone_is_oom_locked(zone)) {
> + ret = 0;
> + goto out;
> + }
> + for_each_populated_zone(zone)
> + zone_set_flag(zone, ZONE_OOM_LOCKED);
> +out:
> + spin_unlock(&zone_scan_lock);
> + return ret;
> +}
> +
> +/*
> + * Clears ZONE_OOM_LOCKED for all system zones so that failed allocation
> + * attempts or page faults may now recall the oom killer, if necessary.
> + */
> +static void clear_system_oom(void)
> +{
> + struct zone *zone;
> +
> + spin_lock(&zone_scan_lock);
> + for_each_populated_zone(zone)
> + zone_clear_flag(zone, ZONE_OOM_LOCKED);
> + spin_unlock(&zone_scan_lock);
> +}
> +
> +
> +#ifdef CONFIG_CGROUP_MEM_RES_CTLR
> +void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask)
> +{
> + unsigned long points = 0;
> + struct task_struct *p;
> +
> + if (!try_set_system_oom())
> + return;
> + read_lock(&tasklist_lock);
> +retry:
> + p = select_bad_process(&points, mem, CONSTRAINT_NONE, NULL);
> + if (PTR_ERR(p) == -1UL)
> + goto out;
> +
> + if (!p)
> + p = current;
> +
> + if (oom_kill_process(p, gfp_mask, 0, points, mem,
> + "Memory cgroup out of memory"))
> + goto retry;
> +out:
> + read_unlock(&tasklist_lock);
> + clear_system_oom();
> +}
> +#endif
> +
> +/*
> * Must be called with tasklist_lock held for read.
> */
> static void __out_of_memory(gfp_t gfp_mask, int order,
> @@ -612,46 +653,9 @@ retry:
> goto retry;
> }
>
> -/*
> - * pagefault handler calls into here because it is out of memory but
> - * doesn't know exactly how or why.
> - */
> -void pagefault_out_of_memory(void)
> -{
> - unsigned long freed = 0;
> -
> - blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
> - if (freed > 0)
> - /* Got some memory back in the last second. */
> - return;
> -
> - /*
> - * If this is from memcg, oom-killer is already invoked.
> - * and not worth to go system-wide-oom.
> - */
> - if (mem_cgroup_oom_called(current))
> - goto rest_and_return;
> -
> - if (sysctl_panic_on_oom)
> - panic("out of memory from page fault. panic_on_oom is selected.\n");
> -
> - read_lock(&tasklist_lock);
> - /* unknown gfp_mask and order */
> - __out_of_memory(0, 0, CONSTRAINT_NONE, NULL);
> - read_unlock(&tasklist_lock);
> -
> - /*
> - * Give "p" a good chance of killing itself before we
> - * retry to allocate memory.
> - */
> -rest_and_return:
> - if (!test_thread_flag(TIF_MEMDIE))
> - schedule_timeout_uninterruptible(1);
> -}
> -
> /**
> * out_of_memory - kill the "best" process when we run out of memory
> - * @zonelist: zonelist pointer
> + * @zonelist: zonelist pointer passed to page allocator
> * @gfp_mask: memory allocation flags
> * @order: amount of memory being requested as a power of 2
> * @nodemask: nodemask passed to page allocator
> @@ -665,7 +669,7 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
> int order, nodemask_t *nodemask)
> {
> unsigned long freed = 0;
> - enum oom_constraint constraint;
> + enum oom_constraint constraint = CONSTRAINT_NONE;
>
> blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
> if (freed > 0)
> @@ -681,7 +685,8 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
> * Check if there were limitations on the allocation (only relevant for
> * NUMA) that may require different handling.
> */
> - constraint = constrained_alloc(zonelist, gfp_mask, nodemask);
> + if (zonelist)
> + constraint = constrained_alloc(zonelist, gfp_mask, nodemask);
> read_lock(&tasklist_lock);
> if (unlikely(sysctl_panic_on_oom)) {
> /*
> @@ -691,6 +696,7 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
> */
> if (constraint == CONSTRAINT_NONE) {
> dump_header(NULL, gfp_mask, order, NULL);
> + read_unlock(&tasklist_lock);
> panic("Out of memory: panic_on_oom is enabled\n");
> }
> }
> @@ -704,3 +710,17 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
> if (!test_thread_flag(TIF_MEMDIE))
> schedule_timeout_uninterruptible(1);
> }
> +
> +/*
> + * The pagefault handler calls here because it is out of memory, so kill a
> + * memory-hogging task. If a populated zone has ZONE_OOM_LOCKED set, a parallel
> + * oom killing is already in progress so do nothing. If a task is found with
> + * TIF_MEMDIE set, it has been killed so do nothing and allow it to exit.
> + */
> +void pagefault_out_of_memory(void)
> +{
> + if (!try_set_system_oom())
> + return;
> + out_of_memory(NULL, 0, 0, NULL);
> + clear_system_oom();
> +}
>
> --
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