On 12.12.18 15:25, Wei Yang wrote:
> drain_all_pages is documented to drain per-cpu pages for a given zone (if
> non-NULL). The current implementation doesn't match the description though.
> It will drain all pcp pages for all zones that happen to have cached pages
> on the same cpu as the given zone. This will leave to premature pcp cache
> draining for zones that are not of an interest for the caller - e.g.
> compaction, hwpoison or memory offline.
>
> This would force the page allocator to take locks and potential lock
> contention as a result.
>
> There is no real reason for this sub-optimal implementnation. Replace
> per-cpu work item with a dedicated structure which contains a pointer to
> zone and pass it over to the worker. This will get the zone information all
> the way down to the worker function and do the right job.
>
> [mhocko@xxxxxxxx: refactor the whole changelog]
>
> Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx>
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> v2:
> * refactor changelog from Michal's suggestion
> ---
> mm/page_alloc.c | 20 ++++++++++++++------
> 1 file changed, 14 insertions(+), 6 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 65db26995466..eb4df3f63f5e 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -96,8 +96,12 @@ int _node_numa_mem_[MAX_NUMNODES];
> #endif
>
> /* work_structs for global per-cpu drains */
s/work_structs/work_struct/ ?
> +struct pcpu_drain {
> + struct zone *zone;
> + struct work_struct work;
> +};
> DEFINE_MUTEX(pcpu_drain_mutex);
> -DEFINE_PER_CPU(struct work_struct, pcpu_drain);
> +DEFINE_PER_CPU(struct pcpu_drain, pcpu_drain);
>
> #ifdef CONFIG_GCC_PLUGIN_LATENT_ENTROPY
> volatile unsigned long latent_entropy __latent_entropy;
> @@ -2596,6 +2600,8 @@ void drain_local_pages(struct zone *zone)
>
> static void drain_local_pages_wq(struct work_struct *work)
> {
> + struct pcpu_drain *drain =
> + container_of(work, struct pcpu_drain, work);
> /*
> * drain_all_pages doesn't use proper cpu hotplug protection so
> * we can race with cpu offline when the WQ can move this from
> @@ -2604,7 +2610,7 @@ static void drain_local_pages_wq(struct work_struct *work)
> * a different one.
> */
> preempt_disable();
> - drain_local_pages(NULL);
> + drain_local_pages(drain->zone);
> preempt_enable();
> }
>
> @@ -2675,12 +2681,14 @@ void drain_all_pages(struct zone *zone)
> }
>
> for_each_cpu(cpu, &cpus_with_pcps) {
> - struct work_struct *work = per_cpu_ptr(&pcpu_drain, cpu);
> - INIT_WORK(work, drain_local_pages_wq);
> - queue_work_on(cpu, mm_percpu_wq, work);
> + struct pcpu_drain *drain = per_cpu_ptr(&pcpu_drain, cpu);
> +
> + drain->zone = zone;
> + INIT_WORK(&drain->work, drain_local_pages_wq);
> + queue_work_on(cpu, mm_percpu_wq, &drain->work);
> }
> for_each_cpu(cpu, &cpus_with_pcps)
> - flush_work(per_cpu_ptr(&pcpu_drain, cpu));
> + flush_work(&per_cpu_ptr(&pcpu_drain, cpu)->work);
>
> mutex_unlock(&pcpu_drain_mutex);
> }
>
Looks good to me!
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
--
Thanks,
David / dhildenb
