On 28.10.21 16:33, Sebastian Andrzej Siewior wrote: > TRANSPARENT_HUGEPAGE: > There are potential non-deterministic delays to an RT thread if a critical > memory region is not THP-aligned and a non-RT buffer is located in the same > hugepage-aligned region. It's also possible for an unrelated thread to migrate > pages belonging to an RT task incurring unexpected page faults due to memory > defragmentation even if khugepaged is disabled. > > Regular HUGEPAGEs are not affected by this can be used. > > NUMA_BALANCING: > There is a non-deterministic delay to mark PTEs PROT_NONE to gather NUMA fault > samples, increased page faults of regions even if mlocked and non-deterministic > delays when migrating pages. > > [Mel Gorman worded 99% of the commit description]. > > Link: https://lore.kernel.org/all/20200304091159.GN3818@xxxxxxxxxxxxxxxxxxx/ > Link: https://lore.kernel.org/all/20211026165100.ahz5bkx44lrrw5pt@xxxxxxxxxxxxx/ > 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..f83e7a0478f7c 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -911,7 +911,7 @@ config NUMA_BALANCING > bool "Memory placement aware NUMA scheduler" > depends on ARCH_SUPPORTS_NUMA_BALANCING > depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY > - depends on SMP && NUMA && MIGRATION > + depends on SMP && NUMA && MIGRATION && !PREEMPT_RT > help > This option adds support for automatic NUMA aware memory/task placement. > The mechanism is quite primitive and is based on migrating memory when > 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 > Makes perfect sense to me. I was also wondering how "dangerous" MIGRATION (and everything depending on it, like CMA, compaction, MEMORY_HOTREMOVE, ...) is for RT recently. Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> -- Thanks, David / dhildenb
