In https://lore.kernel.org/all/20200304091159.GN3818@xxxxxxxxxxxxxxxxxxx/ Mel wrote: | While I ack'd this, an RT application using THP is playing with fire, | I know the RT extension for SLE explicitly disables it from being enabled | at kernel config time. At minimum the critical regions should be mlocked | followed by prctl to disable future THP faults that are non-deterministic, | both from an allocation point of view, and a TLB access point of view. It's | still reasonable to expect a smaller TLB reach for huge pages than | base pages. With TRANSPARENT_HUGEPAGE enabled I haven't seen spikes > 100us in cyclictest. I did have mlock_all() enabled but nothing else. PR_SET_THP_DISABLE remained unchanged (enabled). Is there anything to stress this to be sure or is mlock_all() enough to do THP but leave the mlock() applications alone? Then Mel continued with: | It's a similar hazard with NUMA balancing, an RT application should either | disable balancing globally or set a memory policy that forces it to be | ignored. They should be doing this anyway to avoid non-deterministic | memory access costs due to NUMA artifacts but it wouldn't surprise me | if some applications got it wrong. Usually (often) RT applications are pinned. I would assume that on bigger box the RT tasks are at least pinned to a node. How bad can this get in worst case? cyclictest pins every thread to CPU. I could remove this for testing. What would be a good test to push this to its limit? Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> --- init/Kconfig | 2 +- mm/Kconfig | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/init/Kconfig b/init/Kconfig index edc0a0228f143..8e96817d507c3 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -922,7 +922,7 @@ config NUMA_BALANCING config NUMA_BALANCING_DEFAULT_ENABLED bool "Automatically enable NUMA aware memory/task placement" default y - depends on NUMA_BALANCING + depends on NUMA_BALANCING && !PREEMPT_RT help If set, automatic NUMA balancing will be enabled if running on a NUMA machine. diff --git a/mm/Kconfig b/mm/Kconfig index c150a0c6fce2c..5c5508fafcec5 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -374,7 +374,7 @@ config NOMMU_INITIAL_TRIM_EXCESS config TRANSPARENT_HUGEPAGE bool "Transparent Hugepage Support" - depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE + depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE && !PREEMPT_RT select COMPACTION select XARRAY_MULTI help -- 2.33.1
