On 8/7/25 17:49, Alexander Krabler wrote: > On Thu, 7 Aug 2025 14:21, Hugh Dickins wrote: >> But another idea has just this moment occurred to me: anon THP splitting >> is another user of migration entries. Is it possible that kcompactd is >> not actually the cause of Alexander's issue, but that his RT tasks have >> (bad news! shouldn't be allowed) got anon THPs in them? > > No, we don't have transparent hugepages enabled. > (From Kconfig, this seems not even possible together with PREEMPT_RT.) > > From ftrace events (first message in this thread), we know that kcompactd0 > finally wakes our realtime thread(s). > > Given the information I got from here, the comment on the code [1] > and an older commit message [2], I suspect CMA somehow influences our problem. However, kcompactd doesn't perform CMA allocations, only compaction, in a mode that does not include ISOLATE_UNEVICTABLE. So this is weird. > If there is anything we should enable for better diagnosis (e.g. more ftrace events), > we would be willing to try that out. > > [1] https://elixir.bootlin.com/linux/v6.16/source/mm/compaction.c#L1136 > [2] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e46a28790e594c0876d1a84270926abf75460f61 > > Thanks, > Alexander > > -- > KUKA Deutschland GmbH Board of Directors: Michael Jürgens (Chairman), Dirk Busch, Johan Naten, Hui Zhang Registered Office: Augsburg HRB 14914 > > This e-mail may contain confidential and/or privileged information. If you are not the intended recipient (or have received this e-mail in error) please notify the sender immediately and destroy this e-mail. Any unauthorized copying, disclosure or distribution of contents of this e-mail is strictly forbidden. > > Please consider the environment before printing this e-mail.
