From: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Subject: mm, page_alloc: drain per-cpu pages from workqueue context The per-cpu page allocator can be drained immediately via drain_all_pages() which sends IPIs to every CPU. In the next patch, the per-cpu allocator will only be used for interrupt-safe allocations which prevents draining it from IPI context. This patch uses workqueues to drain the per-cpu lists instead. This is slower but no slowdown during intensive reclaim was measured and the paths that use drain_all_pages() are not that sensitive to performance. This is particularly true as the path would only be triggered when reclaim is failing. It also makes a some sense to avoid storming a machine with IPIs when it's under memory pressure. Arguably, it should be further adjusted so that only one caller at a time is draining pages but it's beyond the scope of the current patch. Link: http://lkml.kernel.org/r/20170123153906.3122-4-mgorman@xxxxxxxxxxxxxxxxxxx Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Cc: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx> Cc: Jesper Dangaard Brouer <brouer@xxxxxxxxxx> Cc: Tejun Heo <tj@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/page_alloc.c | 44 +++++++++++++++++++++++++++++++++++++------- 1 file changed, 37 insertions(+), 7 deletions(-) diff -puN mm/page_alloc.c~mm-page_alloc-drain-per-cpu-pages-from-workqueue-context mm/page_alloc.c --- a/mm/page_alloc.c~mm-page_alloc-drain-per-cpu-pages-from-workqueue-context +++ a/mm/page_alloc.c @@ -2339,19 +2339,21 @@ void drain_local_pages(struct zone *zone drain_pages(cpu); } +static void drain_local_pages_wq(struct work_struct *work) +{ + drain_local_pages(NULL); +} + /* * Spill all the per-cpu pages from all CPUs back into the buddy allocator. * * When zone parameter is non-NULL, spill just the single zone's pages. * - * Note that this code is protected against sending an IPI to an offline - * CPU but does not guarantee sending an IPI to newly hotplugged CPUs: - * on_each_cpu_mask() blocks hotplug and won't talk to offlined CPUs but - * nothing keeps CPUs from showing up after we populated the cpumask and - * before the call to on_each_cpu_mask(). + * Note that this can be extremely slow as the draining happens in a workqueue. */ void drain_all_pages(struct zone *zone) { + struct work_struct __percpu *works; int cpu; /* @@ -2360,6 +2362,17 @@ void drain_all_pages(struct zone *zone) */ static cpumask_t cpus_with_pcps; + /* Workqueues cannot recurse */ + if (current->flags & PF_WQ_WORKER) + return; + + /* + * As this can be called from reclaim context, do not reenter reclaim. + * An allocation failure can be handled, it's simply slower + */ + get_online_cpus(); + works = alloc_percpu_gfp(struct work_struct, GFP_ATOMIC); + /* * We don't care about racing with CPU hotplug event * as offline notification will cause the notified @@ -2390,8 +2403,25 @@ void drain_all_pages(struct zone *zone) else cpumask_clear_cpu(cpu, &cpus_with_pcps); } - on_each_cpu_mask(&cpus_with_pcps, (smp_call_func_t) drain_local_pages, - zone, 1); + + 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); + } + } + put_online_cpus(); } #ifdef CONFIG_HIBERNATION _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
