On Fri, 18 Oct, at 11:56:05AM, Mel Gorman wrote: > 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. > > Cc: stable@xxxxxxxxxxxxxxx # v4.15+ > Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> > --- > mm/page_alloc.c | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) Tested-by: Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx>
