* [PATCH v2] mm: Reset numa stats for boot pagesets
@ 2020-05-07 16:29 Sandipan Das
2020-05-11 11:13 ` Vlastimil Babka
0 siblings, 1 reply; 2+ messages in thread
From: Sandipan Das @ 2020-05-07 16:29 UTC (permalink / raw)
To: akpm; +Cc: linux-mm, khlebnikov, mhocko, vbabka, kirill, aneesh.kumar, srikar
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.
From this point onwards, 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.
Signed-off-by: Sandipan Das <sandipan@linux.ibm.com>
---
The previous version and discussion around it can be found at
https://lore.kernel.org/linux-mm/20200504070304.127361-1-sandipan@linux.ibm.com/
Changes in v2:
- Reset the stats of the boot pagesets instead of explicitly
returning zero as suggested by Vlastimil.
- Changed the subject to reflect the above.
---
mm/page_alloc.c | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 69827d4fa052..1543e32f7e4e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6256,6 +6256,25 @@ void __init setup_per_cpu_pageset(void)
for_each_populated_zone(zone)
setup_zone_pageset(zone);
+#ifdef CONFIG_NUMA
+ if (static_branch_likely(&vm_numa_stat_key)) {
+ struct per_cpu_pageset *pcp;
+ int cpu;
+
+ /*
+ * 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) {
+ 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);
--
2.17.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH v2] mm: Reset numa stats for boot pagesets
2020-05-07 16:29 [PATCH v2] mm: Reset numa stats for boot pagesets Sandipan Das
@ 2020-05-11 11:13 ` Vlastimil Babka
0 siblings, 0 replies; 2+ messages in thread
From: Vlastimil Babka @ 2020-05-11 11:13 UTC (permalink / raw)
To: Sandipan Das, akpm
Cc: linux-mm, khlebnikov, mhocko, kirill, aneesh.kumar, srikar
On 5/7/20 6:29 PM, Sandipan Das wrote:
> 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.
>
> From this point onwards, 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.
>
> Signed-off-by: Sandipan Das <sandipan@linux.ibm.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
With suggestion below.
> ---
>
> The previous version and discussion around it can be found at
> https://lore.kernel.org/linux-mm/20200504070304.127361-1-sandipan@linux.ibm.com/
>
> Changes in v2:
>
> - Reset the stats of the boot pagesets instead of explicitly
> returning zero as suggested by Vlastimil.
>
> - Changed the subject to reflect the above.
>
> ---
> mm/page_alloc.c | 19 +++++++++++++++++++
> 1 file changed, 19 insertions(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 69827d4fa052..1543e32f7e4e 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6256,6 +6256,25 @@ void __init setup_per_cpu_pageset(void)
> for_each_populated_zone(zone)
> setup_zone_pageset(zone);
>
> +#ifdef CONFIG_NUMA
> + if (static_branch_likely(&vm_numa_stat_key)) {
I would just remove this test and do it unconditionally, as the branch can be
only disabled later in boot by a sysctl.
> + struct per_cpu_pageset *pcp;
> + int cpu;
> +
> + /*
> + * 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) {
> + 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);
>
^ permalink raw reply [flat|nested] 2+ messages in thread
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2020-05-11 11:13 ` Vlastimil Babka
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