On Wed 12-10-16 20:33:17, lizf@xxxxxxxxxx wrote:
> From: Michal Hocko <mhocko@xxxxxxxx>
>
> 3.4.113-rc1 review patch. If anyone has any objections, please let me know.
Do not forget to take the follow up fix 564e81a57f97 ("mm, vmstat: fix
wrong WQ sleep when memory reclaim doesn't make any progress")
>
> ------------------
>
>
> commit 373ccbe5927034b55bdc80b0f8b54d6e13fe8d12 upstream.
>
> Tetsuo Handa has reported that the system might basically livelock in
> OOM condition without triggering the OOM killer.
>
> The issue is caused by internal dependency of the direct reclaim on
> vmstat counter updates (via zone_reclaimable) which are performed from
> the workqueue context. If all the current workers get assigned to an
> allocation request, though, they will be looping inside the allocator
> trying to reclaim memory but zone_reclaimable can see stalled numbers so
> it will consider a zone reclaimable even though it has been scanned way
> too much. WQ concurrency logic will not consider this situation as a
> congested workqueue because it relies that worker would have to sleep in
> such a situation. This also means that it doesn't try to spawn new
> workers or invoke the rescuer thread if the one is assigned to the
> queue.
>
> In order to fix this issue we need to do two things. First we have to
> let wq concurrency code know that we are in trouble so we have to do a
> short sleep. In order to prevent from issues handled by 0e093d99763e
> ("writeback: do not sleep on the congestion queue if there are no
> congested BDIs or if significant congestion is not being encountered in
> the current zone") we limit the sleep only to worker threads which are
> the ones of the interest anyway.
>
> The second thing to do is to create a dedicated workqueue for vmstat and
> mark it WQ_MEM_RECLAIM to note it participates in the reclaim and to
> have a spare worker thread for it.
>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> Reported-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Cc: Tejun Heo <tj@xxxxxxxxxx>
> Cc: Cristopher Lameter <clameter@xxxxxxx>
> Cc: Joonsoo Kim <js1304@xxxxxxxxx>
> Cc: Arkadiusz Miskiewicz <arekm@xxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> [lizf: Backported to 3.4: adjust context]
> Signed-off-by: Zefan Li <lizefan@xxxxxxxxxx>
> ---
> mm/backing-dev.c | 19 ++++++++++++++++---
> mm/vmstat.c | 6 ++++--
> 2 files changed, 20 insertions(+), 5 deletions(-)
>
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index dd8e2aa..3f54b7d 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -843,8 +843,9 @@ EXPORT_SYMBOL(congestion_wait);
> * jiffies for either a BDI to exit congestion of the given @sync queue
> * or a write to complete.
> *
> - * In the absence of zone congestion, cond_resched() is called to yield
> - * the processor if necessary but otherwise does not sleep.
> + * In the absence of zone congestion, a short sleep or a cond_resched is
> + * performed to yield the processor and to allow other subsystems to make
> + * a forward progress.
> *
> * The return value is 0 if the sleep is for the full timeout. Otherwise,
> * it is the number of jiffies that were still remaining when the function
> @@ -864,7 +865,19 @@ long wait_iff_congested(struct zone *zone, int sync, long timeout)
> */
> if (atomic_read(&nr_bdi_congested[sync]) == 0 ||
> !zone_is_reclaim_congested(zone)) {
> - cond_resched();
> +
> + /*
> + * Memory allocation/reclaim might be called from a WQ
> + * context and the current implementation of the WQ
> + * concurrency control doesn't recognize that a particular
> + * WQ is congested if the worker thread is looping without
> + * ever sleeping. Therefore we have to do a short sleep
> + * here rather than calling cond_resched().
> + */
> + if (current->flags & PF_WQ_WORKER)
> + schedule_timeout(1);
> + else
> + cond_resched();
>
> /* In case we scheduled, work out time remaining */
> ret = timeout - (jiffies - start);
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 7db1b9b..e89c0f6 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1139,13 +1139,14 @@ static const struct file_operations proc_vmstat_file_operations = {
> #endif /* CONFIG_PROC_FS */
>
> #ifdef CONFIG_SMP
> +static struct workqueue_struct *vmstat_wq;
> static DEFINE_PER_CPU(struct delayed_work, vmstat_work);
> int sysctl_stat_interval __read_mostly = HZ;
>
> static void vmstat_update(struct work_struct *w)
> {
> refresh_cpu_vm_stats(smp_processor_id());
> - schedule_delayed_work(&__get_cpu_var(vmstat_work),
> + queue_delayed_work(vmstat_wq, &__get_cpu_var(vmstat_work),
> round_jiffies_relative(sysctl_stat_interval));
> }
>
> @@ -1154,7 +1155,7 @@ static void __cpuinit start_cpu_timer(int cpu)
> struct delayed_work *work = &per_cpu(vmstat_work, cpu);
>
> INIT_DELAYED_WORK_DEFERRABLE(work, vmstat_update);
> - schedule_delayed_work_on(cpu, work, __round_jiffies_relative(HZ, cpu));
> + queue_delayed_work_on(cpu, vmstat_wq, work, __round_jiffies_relative(HZ, cpu));
> }
>
> /*
> @@ -1204,6 +1205,7 @@ static int __init setup_vmstat(void)
>
> register_cpu_notifier(&vmstat_notifier);
>
> + vmstat_wq = alloc_workqueue("vmstat", WQ_FREEZABLE|WQ_MEM_RECLAIM, 0);
> for_each_online_cpu(cpu)
> start_cpu_timer(cpu);
> #endif
> --
> 1.9.1
>
--
Michal Hocko
SUSE Labs
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