The patch titled
Subject: mm, page_alloc: drain per-cpu pages from workqueue context
has been added to the -mm tree. Its filename is
mm-page_alloc-drain-per-cpu-pages-from-workqueue-context.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-page_alloc-drain-per-cpu-pages-from-workqueue-context.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-page_alloc-drain-per-cpu-pages-from-workqueue-context.patch
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------------------------------------------------------
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>
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
_
Patches currently in -mm which might be from mgorman@xxxxxxxxxxxxxxxxxxx are
mm-page_alloc-split-buffered_rmqueue.patch
mm-page_alloc-split-alloc_pages_nodemask.patch
mm-page_alloc-drain-per-cpu-pages-from-workqueue-context.patch
mm-page_alloc-only-use-per-cpu-allocator-for-irq-safe-requests.patch
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