From: Sandipan Das <sandipan@xxxxxxxxxxxxx>
Subject: mm/page_alloc.c: reset numa stats for boot pagesets
Initially, the per-cpu pagesets of each zone are set to the boot pagesets.
The real pagesets are allocated later but before that happens, page
allocations do occur and the numa stats for the boot pagesets get
incremented since they are common to all zones at that point.
The real pagesets, however, are allocated for the populated zones only.
Unpopulated zones, like those associated with memory-less nodes, continue
using the boot pageset and end up skewing the numa stats of the
corresponding node.
E.g.
$ numactl -H
available: 2 nodes (0-1)
node 0 cpus: 0 1 2 3
node 0 size: 0 MB
node 0 free: 0 MB
node 1 cpus: 4 5 6 7
node 1 size: 8131 MB
node 1 free: 6980 MB
node distances:
node 0 1
0: 10 40
1: 40 10
$ numastat
node0 node1
numa_hit 108 56495
numa_miss 0 0
numa_foreign 0 0
interleave_hit 0 4537
local_node 108 31547
other_node 0 24948
Hence, the boot pageset stats need to be cleared after the real pagesets
are allocated.
After this point, the stats of the boot pagesets do not change as page
allocations requested for a memory-less node will either fail (if
__GFP_THISNODE is used) or get fulfilled by a preferred zone of a
different node based on the fallback zonelist.
[sandipan@xxxxxxxxxxxxx: v3]
Link: http://lkml.kernel.org/r/20200511170356.162531-1-sandipan@xxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/9c9c2d1b15e37f6e6bf32f99e3100035e90c4ac9.1588868430.git.sandipan@xxxxxxxxxxxxx
Signed-off-by: Sandipan Das <sandipan@xxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: "Kirill A . Shutemov" <kirill@xxxxxxxxxxxxx>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
--- a/mm/page_alloc.c~mm-reset-numa-stats-for-boot-pagesets
+++ a/mm/page_alloc.c
@@ -6250,10 +6250,25 @@ void __init setup_per_cpu_pageset(void)
{
struct pglist_data *pgdat;
struct zone *zone;
+ int __maybe_unused cpu;
for_each_populated_zone(zone)
setup_zone_pageset(zone);
+#ifdef CONFIG_NUMA
+ /*
+ * Unpopulated zones continue using the boot pagesets.
+ * The numa stats for these pagesets need to be reset.
+ * Otherwise, they will end up skewing the stats of
+ * the nodes these zones are associated with.
+ */
+ for_each_possible_cpu(cpu) {
+ struct per_cpu_pageset *pcp = &per_cpu(boot_pageset, cpu);
+ memset(pcp->vm_numa_stat_diff, 0,
+ sizeof(pcp->vm_numa_stat_diff));
+ }
+#endif
+
for_each_online_pgdat(pgdat)
pgdat->per_cpu_nodestats =
alloc_percpu(struct per_cpu_nodestat);
_
