On Mon 06-03-17 11:24:10, Johannes Weiner wrote:
[...]
> >From e126db716926ff353b35f3a6205bd5853e01877b Mon Sep 17 00:00:00 2001
> From: Johannes Weiner <hannes@xxxxxxxxxxx>
> Date: Mon, 6 Mar 2017 10:53:59 -0500
> Subject: [PATCH] mm: fix 100% CPU kswapd busyloop on unreclaimable nodes fix
>
> Check kswapd failure against the cumulative nr_reclaimed count, not
> against the count from the lowest priority iteration.
>
> Suggested-by: Minchan Kim <minchan@xxxxxxxxxx>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> ---
> mm/vmscan.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index ddcff8a11c1e..b834b2dd4e19 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -3179,9 +3179,9 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
> count_vm_event(PAGEOUTRUN);
>
> do {
> + unsigned long nr_reclaimed = sc.nr_reclaimed;
> bool raise_priority = true;
>
> - sc.nr_reclaimed = 0;
> sc.reclaim_idx = classzone_idx;
>
> /*
> @@ -3271,7 +3271,8 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
> * Raise priority if scanning rate is too low or there was no
> * progress in reclaiming pages
> */
> - if (raise_priority || !sc.nr_reclaimed)
> + nr_reclaimed = sc.nr_reclaimed - nr_reclaimed;
> + if (raise_priority || !nr_reclaimed)
> sc.priority--;
> } while (sc.priority >= 1);
>
I would rather not play with the sc state here. From a quick look at
least
/*
* Fragmentation may mean that the system cannot be rebalanced for
* high-order allocations. If twice the allocation size has been
* reclaimed then recheck watermarks only at order-0 to prevent
* excessive reclaim. Assume that a process requested a high-order
* can direct reclaim/compact.
*/
if (sc->order && sc->nr_reclaimed >= compact_gap(sc->order))
sc->order = 0;
does rely on the value. Wouldn't something like the following be safer?
---
diff --git a/mm/vmscan.c b/mm/vmscan.c
index c15b2e4c47ca..b731f24fed12 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3183,6 +3183,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
.may_unmap = 1,
.may_swap = 1,
};
+ bool reclaimable = false;
count_vm_event(PAGEOUTRUN);
do {
@@ -3274,6 +3275,9 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
if (try_to_freeze() || kthread_should_stop())
break;
+ if (sc.nr_reclaimed)
+ reclaimable = true;
+
/*
* Raise priority if scanning rate is too low or there was no
* progress in reclaiming pages
@@ -3282,7 +3286,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
sc.priority--;
} while (sc.priority >= 1);
- if (!sc.nr_reclaimed)
+ if (!reclaimable)
pgdat->kswapd_failures++;
out:
--
Michal Hocko
SUSE Labs
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