On Wed 23-10-19 13:34:22, Waiman Long wrote:
> With a threshold of 100000, it is still possible that the zone lock
> will be held for a very long time in the worst case scenario where all
> the counts are just below the threshold. With up to 6 migration types
> and 11 orders, it means up to 6.6 millions.
>
> Track the total number of list iterations done since the acquisition
> of the zone lock and release it whenever 100000 iterations or more have
> been completed. This will cap the lock hold time to no more than 200,000
> list iterations.
>
> Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
> ---
> mm/vmstat.c | 18 ++++++++++++++----
> 1 file changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 57ba091e5460..c5b82fdf54af 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1373,6 +1373,7 @@ static void pagetypeinfo_showfree_print(struct seq_file *m,
> pg_data_t *pgdat, struct zone *zone)
> {
> int order, mtype;
> + unsigned long iteration_count = 0;
>
> for (mtype = 0; mtype < MIGRATE_TYPES; mtype++) {
> seq_printf(m, "Node %4d, zone %8s, type %12s ",
> @@ -1397,15 +1398,24 @@ static void pagetypeinfo_showfree_print(struct seq_file *m,
> * of pages in this order should be more than
> * sufficient
> */
> - if (++freecount >= 100000) {
> + if (++freecount > 100000) {
> overflow = true;
> - spin_unlock_irq(&zone->lock);
> - cond_resched();
> - spin_lock_irq(&zone->lock);
> + freecount--;
> break;
> }
> }
> seq_printf(m, "%s%6lu ", overflow ? ">" : "", freecount);
> + /*
> + * Take a break and release the zone lock when
> + * 100000 or more entries have been iterated.
> + */
> + iteration_count += freecount;
> + if (iteration_count >= 100000) {
> + iteration_count = 0;
> + spin_unlock_irq(&zone->lock);
> + cond_resched();
> + spin_lock_irq(&zone->lock);
> + }
Aren't you overengineering this a bit? If you are still worried then we
can simply cond_resched for each order
diff --git a/mm/vmstat.c b/mm/vmstat.c
index c156ce24a322..ddb89f4e0486 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1399,13 +1399,13 @@ static void pagetypeinfo_showfree_print(struct seq_file *m,
*/
if (++freecount >= 100000) {
overflow = true;
- spin_unlock_irq(&zone->lock);
- cond_resched();
- spin_lock_irq(&zone->lock);
break;
}
}
seq_printf(m, "%s%6lu ", overflow ? ">" : "", freecount);
+ spin_unlock_irq(&zone->lock);
+ cond_resched();
+ spin_lock_irq(&zone->lock);
}
seq_putc(m, '\n');
}
I do not have a strong opinion here but I can fold this into my patch 2.
--
Michal Hocko
SUSE Labs
