On Wed, Jul 10, 2019 at 7:41 AM Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> wrote: > > Hi, > > I've been looking at the following trace: > | cyclicte-526 0d...2.. 6876070 603us : finish_task_switch <-__schedule > | cyclicte-526 0....2.. 6876070 605us : preempt_count_sub <-finish_task_switch > | cyclicte-526 0....1.. 6876070 607us : preempt_count_sub <-schedule > | cyclicte-526 0....... 6876070 610us : finish_wait <-put_and_wait_on_page_locked > > I see put_and_wait_on_page_locked after schedule and didn't expect that. > cyclictest then blocks on a lock and switches to `kcompact'. Once it > finishes, it switches back to cyclictest: > | cyclicte-526 0....... 6876070 853us : rt_spin_unlock <-put_and_wait_on_page_locked > | cyclicte-526 0....... 6876070 854us : migrate_enable <-rt_spin_unlock > | cyclicte-526 0....... 6876070 860us : up_read <-do_page_fault > | cyclicte-526 0....... 6876070 861us : __up_read <-do_page_fault > | cyclicte-526 0d...... 6876070 867us : do_PrefetchAbort <-ret_from_exception > | cyclicte-526 0d...... 6876070 868us : do_page_fault <-do_PrefetchAbort > | cyclicte-526 0....... 6876070 870us : down_read_trylock <-do_page_fault > | cyclicte-526 0....... 6876070 872us : __down_read_trylock <-do_page_fault > … > | cyclicte-526 0....... 6876070 914us : __up_read <-do_page_fault > | cyclicte-526 0....... 6876070 923us : sys_clock_gettime32 <-ret_fast_syscall > | cyclicte-526 0....... 6876070 925us : posix_ktime_get_ts <-sys_clock_gettime32 > > I did not expect a pagefault with mlockall(). I assume it has to do with > memory compaction. I have > | CONFIG_COMPACTION=y > | CONFIG_MIGRATION=y > > and Kconfig says: > |config COMPACTION > … > | You shouldn't > | disable this option unless there really is a strong reason for > | it and then we would be really interested to hear about that at > | linux-mm@xxxxxxxxx. > > Shouldn't COMPACTION avoid touching/moving mlock()ed pages? compaction should not isolate unevictable pages unless you have /proc/sys/vm/compact_unevictable_allowed set. > > Sebastian >
