[PATCH v5 8/8] mm: add vmstat counters for tracking PCP drains

[Gilad Ben-Yossef]

This patch introduces two new vmstat counters: pcp_global_drain
that counts the number of times a per-cpu pages global drain was
requested and pcp_global_ipi_saved that counts the number of times
the number of CPUs with per-cpu pages in any zone were less then
1/2 of the number of online CPUs.

The patch purpose is to show the usefulness of only sending an IPI
asking to drain per-cpu pages to CPUs that actually have them
instead of a blind global IPI. It is probably not useful by itself.

Signed-off-by: Gilad Ben-Yossef <gilad@xxxxxxxxxxxxx>
CC: Christoph Lameter <cl@xxxxxxxxx>
CC: Chris Metcalf <cmetcalf@xxxxxxxxxx>
CC: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
CC: Frederic Weisbecker <fweisbec@xxxxxxxxx>
CC: linux-mm@xxxxxxxxx
CC: Pekka Enberg <penberg@xxxxxxxxxx>
CC: Matt Mackall <mpm@xxxxxxxxxxx>
CC: Sasha Levin <levinsasha928@xxxxxxxxx>
CC: Rik van Riel <riel@xxxxxxxxxx>
CC: Andi Kleen <andi@xxxxxxxxxxxxxx>
CC: Mel Gorman <mel@xxxxxxxxx>
CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
CC: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
CC: Avi Kivity <avi@xxxxxxxxxx>
---
 include/linux/vm_event_item.h |    1 +
 mm/page_alloc.c               |    4 ++++
 mm/vmstat.c                   |    2 ++
 3 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 03b90cd..3657f6f 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -58,6 +58,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 		THP_COLLAPSE_ALLOC_FAILED,
 		THP_SPLIT,
 #endif
+		PCP_GLOBAL_DRAIN, PCP_GLOBAL_IPI_SAVED,
 		NR_VM_EVENT_ITEMS
 };
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 092c331..4ca6bfa 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1140,6 +1140,10 @@ void drain_all_pages(void)
 				cpumask_clear_cpu(cpu, cpus_with_pcps);
 		}
 	on_each_cpu_mask(cpus_with_pcps, drain_local_pages, NULL, 1);
+
+	count_vm_event(PCP_GLOBAL_DRAIN);
+	if (cpumask_weight(cpus_with_pcps) < (cpumask_weight(cpu_online_mask) / 2))
+		count_vm_event(PCP_GLOBAL_IPI_SAVED);
 }
 
 #ifdef CONFIG_HIBERNATION
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 8fd603b..daf632c 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -786,6 +786,8 @@ const char * const vmstat_text[] = {
 	"thp_collapse_alloc_failed",
 	"thp_split",
 #endif
+	"pcp_global_drain",
+	"pcp_global_ipi_saved"
 
 #endif /* CONFIG_VM_EVENTS_COUNTERS */
 };
-- 
1.7.0.4

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