From: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
commit 3e8fc0075e24338b1117cdff6a79477427b8dbed upstream.
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
[mgorman@xxxxxxxxxxxxxxxxxxx: fix merge/linkage snafu]
Link: http://lkml.kernel.org/r/20191023084705.GD3016@techsingularity.netLink: 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>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
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>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2051,6 +2051,14 @@ static void reserve_highatomic_pageblock
unsigned long max_managed, flags;
/*
+ * 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);
+
+ /*
* Limit the number reserved to 1 pageblock or roughly 1% of a zone.
* Check is race-prone but harmless.
*/
@@ -7385,7 +7393,6 @@ void free_contig_range(unsigned long pfn
}
#endif
-#ifdef CONFIG_MEMORY_HOTPLUG
/*
* The zone indicated has a new number of managed_pages; batch sizes and percpu
* page high values need to be recalulated.
@@ -7399,7 +7406,6 @@ void __meminit zone_pcp_update(struct zo
per_cpu_ptr(zone->pageset, cpu));
mutex_unlock(&pcp_batch_high_lock);
}
-#endif
void zone_pcp_reset(struct zone *zone)
{
