On Fri, 18 Oct 2019 15:09:59 +0100 Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> wrote:
> > > Cc: stable@xxxxxxxxxxxxxxx # v4.15+
> >
> > Hmm, are you sure about 4.15? Doesn't this go all the way down to
> > deferred initialization? I do not see any recent changes on when
> > setup_per_cpu_pageset is called.
> >
>
> No, I'm not 100% sure. It looks like this was always an issue from the
> code but did not happen on at least one 4.12-based distribution kernel for
> reasons that are non-obvious. Either way, the tag should have been "v4.1+"
I could mark
mm-pcp-share-common-code-between-memory-hotplug-and-percpu-sysctl-handler.patch
mm-meminit-recalculate-pcpu-batch-and-high-limits-after-init-completes.patch
as Cc: <stable@xxxxxxxxxxxxxxx> [4.1+]
But for backporting purposes it's a bit cumbersome that [2/3] is the
important patch. I think I'll switch the ordering so that
mm-meminit-recalculate-pcpu-batch-and-high-limits-after-init-completes.patch
is the first patch and the other two can be queued for 5.5-rc1, OK?
Also, is a Reported-by:Matt appropriate here?
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 on each node. 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-v1r1
Amean user-256 13249.50 ( 0.00%) 15928.40 * -20.22%*
Amean syst-256 14760.30 ( 0.00%) 4551.77 * 69.16%*
Amean elsp-256 162.42 ( 0.00%) 118.46 * 27.06%*
Stddev user-256 42.97 ( 0.00%) 50.83 ( -18.30%)
Stddev syst-256 336.87 ( 0.00%) 33.70 ( 90.00%)
Stddev elsp-256 2.46 ( 0.00%) 0.81 ( 67.01%)
5.4.0-rc3 5.4.0-rc3
vanillaresetpcpu-v1r1
Duration User 39766.24 47802.92
Duration System 44298.10 13671.93
Duration Elapsed 519.11 387.65
The patch reduces system CPU usage by 69.16% and total build time by
27.06%. The variance of system CPU usage is also much reduced.
Link: http://lkml.kernel.org/r/20191018105606.3249-3-mgorman@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Tested-by: Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [4.1+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
--- a/mm/page_alloc.c~mm-meminit-recalculate-pcpu-batch-and-high-limits-after-init-completes
+++ a/mm/page_alloc.c
@@ -1818,6 +1818,14 @@ static int __init deferred_init_memmap(v
*/
while (spfn < epfn)
nr_pages += deferred_init_maxorder(&i, zone, &spfn, &epfn);
+
+ /*
+ * 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.
+ */
+ zone_pcp_update(zone);
+
zone_empty:
pgdat_resize_unlock(pgdat, &flags);
@@ -8514,7 +8522,6 @@ void free_contig_range(unsigned long pfn
WARN(count != 0, "%d pages are still in use!\n", count);
}
-#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.
@@ -8528,7 +8535,6 @@ 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)
{
_
