Le Mon, Aug 05, 2024 at 04:53:51PM +0200, Vlastimil Babka a écrit : > If you mean the loop in kcompactd_init() then indeed, but we also have a > hook in online_pages() to start new threads on newly onlined nodes, so > that's not a problem. > > The problem (I think) I see is cpumask_of_node(pgdat->node_id) is a snapshot > of cpus running on the NUMA node the time, and is never updated later as new > cpus might be brought up. Oh I see now... > > kcompactd_cpu_online() does try to update that when cpus are onlined (in a > clumsy way), there was nothing like that for kswapd and after your series > this update is also removed for kcompactd. Ok... > > > If all users of preferred affinity were to use NUMA nodes, it could be > > a good idea to do a flavour of kernel/smpboot.c which would handle > > per-node kthreads instead of per-cpu kthreads. I initially thought > > about that. It would have handled all the lifecycle of those kthreads, > > including creation, against hotplug. Unfortunately RCU doesn't rely on > > per-NUMA nodes but rather use its own tree. > > > > If there be more users of real per NUMA nodes kthreads than kswapd and > > kcompactd, of course that would be much worth considering. > > Yeah it's not that compelling, but a way to update the preferred affine mask > in response to cpu hotplug events, that kswapd and kcompactd could use, > would be sufficient. And maybe more widely useful. > > I guess there could be a callback defined for kthread to provide a new > preferred_affinity, that you'd call from kthreads_hotplug_update() ? > And kcompactd and kswapd could both use the same callback that interprets > kthread_data() as pgdat and fetches a new cpumask of it? It's too bad we don't have a way to have a cpumask_possible_of_node(). I've looked into the guts of numa but that doesn't look easy to do. Or there could be kthread_set_preferred_node()... ? Thanks. > > > Thanks. >
