Re: [PATCH 4/6] sched/isolation: Drain per-CPU LRU batches when CPUs become isolated

[Leonardo Bras]

On Tue, Nov 03, 2026 at 03:10:22PM +0100, Frederic Weisbecker wrote:
> Le Tue, Nov 03, 2026 at 08:59:38PM +1300, Matthew Ruffell a écrit :
> > From: Caron Wills <caron.wills@xxxxxxxxxx>
> > 
> > Isolated CPUs no longer batch folios in their per-CPU LRU caches, so
> > that __lru_add_drain_all() never has to queue work on them. Boot time
> > isolation (isolcpus=, nohz_full=) takes effect before any folio is
> > batched, but a cpuset isolated partition can be created at runtime and
> > the affected CPUs may still hold folios in their batches from before.
> > Those would linger until the CPU happens to drain locally, and the next
> > lru_add_drain_all() would fall back to queueing work on the now isolated
> > CPU, which is exactly what must be avoided.
> > 
> > Drain all batches once from housekeeping_update(), right after the
> > HK_TYPE_DOMAIN mask has been updated and next to the vmstat and memcg
> > workqueue flushes that exist for the same reason, so that newly isolated
> > CPUs start out with empty batches.
> > 
> > Link: https://bugs.launchpad.net/bugs/2165410
> > Signed-off-by: Caron Wills <caron.wills@xxxxxxxxxx>
> > Signed-off-by: Matthew Ruffell <matthew.ruffell@xxxxxxxxxxxxx>
> 
> There was this patchset:
> https://lore.kernel.org/lkml/20260519012754.240804-1-leobras.c@xxxxxxxxx/
> 
> Leonardo, do you plan a v5?

Yeah, working on that.
Hopefully should be tested by the end of this month.

Thanks!
Leo