Messages in this thread Patch in this message | | | Date | Wed, 25 Jan 2017 16:08:02 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH] mm, page_alloc: Use static global work_struct for draining per-cpu pages |
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On Wed, 25 Jan 2017 08:30:38 +0000 Mel Gorman <mgorman@techsingularity.net> wrote:
> As suggested by Vlastimil Babka and Tejun Heo, this patch uses a static > work_struct to co-ordinate the draining of per-cpu pages on the workqueue. > Only one task can drain at a time but this is better than the previous > scheme that allowed multiple tasks to send IPIs at a time. > > One consideration is whether parallel requests should synchronise against > each other. This patch does not synchronise for a global drain as the common > case for such callers is expected to be multiple parallel direct reclaimers > competing for pages when the watermark is close to min. Draining the per-cpu > list is unlikely to make much progress and serialising the drain is of > dubious merit. Drains are synchonrised for callers such as memory hotplug > and CMA that care about the drain being complete when the function returns. > > ... > > @@ -2402,24 +2415,16 @@ void drain_all_pages(struct zone *zone) > cpumask_clear_cpu(cpu, &cpus_with_pcps); > } > > - if (works) { > - for_each_cpu(cpu, &cpus_with_pcps) { > - struct work_struct *work = per_cpu_ptr(works, cpu); > - INIT_WORK(work, drain_local_pages_wq); > - schedule_work_on(cpu, work); > - } > - for_each_cpu(cpu, &cpus_with_pcps) > - flush_work(per_cpu_ptr(works, cpu)); > - } else { > - for_each_cpu(cpu, &cpus_with_pcps) { > - struct work_struct work; > - > - INIT_WORK(&work, drain_local_pages_wq); > - schedule_work_on(cpu, &work); > - flush_work(&work); > - } > + for_each_cpu(cpu, &cpus_with_pcps) { > + struct work_struct *work = per_cpu_ptr(&pcpu_drain, cpu); > + INIT_WORK(work, drain_local_pages_wq);
It's strange to repeatedly run INIT_WORK() in this fashion. Overwriting an atomic_t which should already be zero, initializing a list_head which should already be in the initialized state...
Can we instead do this a single time in init code?
> + schedule_work_on(cpu, work); > } > + for_each_cpu(cpu, &cpus_with_pcps) > + flush_work(per_cpu_ptr(&pcpu_drain, cpu)); > + > put_online_cpus(); > + mutex_unlock(&pcpu_drain_mutex); > }
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