On Mon 10-02-25 18:50:26, Hillf Danton wrote:
> On Sun, 9 Feb 2025 23:30:04 +0100 Frederic Weisbecker <frederic@xxxxxxxxxx>
> > @@ -769,6 +772,9 @@ static bool cpu_needs_drain(unsigned int cpu)
> > {
> > struct cpu_fbatches *fbatches = &per_cpu(cpu_fbatches, cpu);
> >
> > + if (!housekeeping_cpu(cpu, HK_TYPE_KERNEL_NOISE))
> > + return false;
> > +
> > /* Check these in order of likelihood that they're not zero */
> > return folio_batch_count(&fbatches->lru_add) ||
> > folio_batch_count(&fbatches->lru_move_tail) ||
> > --
> > 2.46.0
>
> Nit, I'd like to add a debug line to test your assumption that
> isolated tasks are pinned to a single nohz_full CPU.
Why? And why would you like to add a trivial VM_BUG_ON vector to the
kernel?
> --- x/mm/swap.c
> +++ y/mm/swap.c
> @@ -767,9 +767,10 @@ static void lru_add_drain_per_cpu(struct
> static bool cpu_needs_drain(unsigned int cpu)
> {
> struct cpu_fbatches *fbatches = &per_cpu(cpu_fbatches, cpu);
> + bool yes;
>
> /* Check these in order of likelihood that they're not zero */
> - return folio_batch_count(&fbatches->lru_add) ||
> + yes = folio_batch_count(&fbatches->lru_add) ||
> folio_batch_count(&fbatches->lru_move_tail) ||
> folio_batch_count(&fbatches->lru_deactivate_file) ||
> folio_batch_count(&fbatches->lru_deactivate) ||
> @@ -777,6 +778,12 @@ static bool cpu_needs_drain(unsigned int
> folio_batch_count(&fbatches->lru_activate) ||
> need_mlock_drain(cpu) ||
> has_bh_in_lru(cpu, NULL);
> +
> + if (!housekeeping_cpu(cpu, HK_TYPE_KERNEL_NOISE)) {
> + VM_BUG_ON(yes);
> + return false;
> + }
> + return yes;
> }
>
> /*
--
Michal Hocko
SUSE Labs
