The patch titled
Subject: mm, meminit: recalculate pcpu batch and high limits after init completes
has been added to the -mm tree. Its filename is
mm-meminit-recalculate-pcpu-batch-and-high-limits-after-init-completes.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-meminit-recalculate-pcpu-batch-and-high-limits-after-init-completes.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-meminit-recalculate-pcpu-batch-and-high-limits-after-init-completes.patch
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------------------------------------------------------
From: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Subject: mm, meminit: recalculate pcpu batch and high limits after init completes
Deferred memory initialisation updates zone->managed_pages during the
initialisation phase but before that finishes, the per-cpu page allocator
(pcpu) calculates the number of pages allocated/freed in batches as well
as the maximum number of pages allowed on a per-cpu list. As
zone->managed_pages is not up to date yet, the pcpu initialisation
calculates inappropriately low batch and high values.
This increases zone lock contention quite severely in some cases with the
degree of severity depending on how many CPUs share a local zone and the
size of the zone. A private report indicated that kernel build times were
excessive with extremely high system CPU usage. A perf profile indicated
that a large chunk of time was lost on zone->lock contention.
This patch recalculates the pcpu batch and high values after deferred
initialisation completes for every populated zone in the system. It was
tested on a 2-socket AMD EPYC 2 machine using a kernel compilation
workload -- allmodconfig and all available CPUs.
mmtests configuration: config-workload-kernbench-max Configuration was
modified to build on a fresh XFS partition.
kernbench
5.4.0-rc3 5.4.0-rc3
vanilla resetpcpu-v2
Amean user-256 13249.50 ( 0.00%) 16401.31 * -23.79%*
Amean syst-256 14760.30 ( 0.00%) 4448.39 * 69.86%*
Amean elsp-256 162.42 ( 0.00%) 119.13 * 26.65%*
Stddev user-256 42.97 ( 0.00%) 19.15 ( 55.43%)
Stddev syst-256 336.87 ( 0.00%) 6.71 ( 98.01%)
Stddev elsp-256 2.46 ( 0.00%) 0.39 ( 84.03%)
5.4.0-rc3 5.4.0-rc3
vanilla resetpcpu-v2
Duration User 39766.24 49221.79
Duration System 44298.10 13361.67
Duration Elapsed 519.11 388.87
The patch reduces system CPU usage by 69.86% and total build time by
26.65%. The variance of system CPU usage is also much reduced.
Before, this was the breakdown of batch and high values over all zones was.
256 batch: 1
256 batch: 63
512 batch: 7
256 high: 0
256 high: 378
512 high: 42
512 pcpu pagesets had a batch limit of 7 and a high limit of 42. After
the patch:
256 batch: 1
768 batch: 63
256 high: 0
768 high: 378
Link: http://lkml.kernel.org/r/20191021094808.28824-2-mgorman@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Qian Cai <cai@xxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [4.1+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 8 ++++++++
1 file changed, 8 insertions(+)
--- a/mm/page_alloc.c~mm-meminit-recalculate-pcpu-batch-and-high-limits-after-init-completes
+++ a/mm/page_alloc.c
@@ -1948,6 +1948,14 @@ void __init page_alloc_init_late(void)
wait_for_completion(&pgdat_init_all_done_comp);
/*
+ * The number of managed pages has changed due to the initialisation
+ * so the pcpu batch and high limits needs to be updated or the limits
+ * will be artificially small.
+ */
+ for_each_populated_zone(zone)
+ zone_pcp_update(zone);
+
+ /*
* We initialized the rest of the deferred pages. Permanently disable
* on-demand struct page initialization.
*/
_
Patches currently in -mm which might be from mgorman@xxxxxxxxxxxxxxxxxxx are
mm-meminit-recalculate-pcpu-batch-and-high-limits-after-init-completes.patch
mm-pcp-share-common-code-between-memory-hotplug-and-percpu-sysctl-handler.patch
mm-pcpu-make-zone-pcp-updates-and-reset-internal-to-the-mm.patch
