From: Zlatko Calusic <zlatko.calusic@xxxxxxxx>
Currently we take a short nap (HZ/10) and wait for congestion to clear
before taking another pass with lower priority in balance_pgdat(). But
we do that only for the highest zone that we encounter is unbalanced
and congested.
This patch changes that to wait on all congested zones in a single
pass in the hope that it will save us some scanning that way. Also we
take a nap as soon as congested zone is encountered and sc.priority <
DEF_PRIORITY - 2 (aka kswapd in trouble).
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Minchan Kim <minchan.kim@xxxxxxxxx>
Signed-off-by: Zlatko Calusic <zlatko.calusic@xxxxxxxx>
---
The patch is against the mm tree. Make sure that
mm-avoid-calling-pgdat_balanced-needlessly.patch is applied first (not
yet in the mmotm tree). Tested on half a dozen systems with different
workloads for the last few days, working really well!
mm/vmscan.c | 35 ++++++++++++-----------------------
1 file changed, 12 insertions(+), 23 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 002ade6..1c5d38a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2565,7 +2565,6 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
int *classzone_idx)
{
bool pgdat_is_balanced = false;
- struct zone *unbalanced_zone;
int i;
int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
unsigned long total_scanned;
@@ -2596,9 +2595,6 @@ loop_again:
do {
unsigned long lru_pages = 0;
- int has_under_min_watermark_zone = 0;
-
- unbalanced_zone = NULL;
/*
* Scan in the highmem->dma direction for the highest
@@ -2739,15 +2735,20 @@ loop_again:
}
if (!zone_balanced(zone, testorder, 0, end_zone)) {
- unbalanced_zone = zone;
- /*
- * We are still under min water mark. This
- * means that we have a GFP_ATOMIC allocation
- * failure risk. Hurry up!
- */
+ if (total_scanned && sc.priority < DEF_PRIORITY - 2) {
+ /* OK, kswapd is getting into trouble. */
if (!zone_watermark_ok_safe(zone, order,
min_wmark_pages(zone), end_zone, 0))
- has_under_min_watermark_zone = 1;
+ /*
+ * We are still under min water mark.
+ * This means that we have a GFP_ATOMIC
+ * allocation failure risk. Hurry up!
+ */
+ count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
+ else
+ /* Take a nap if a zone is congested. */
+ wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);
+ }
} else {
/*
* If a zone reaches its high watermark,
@@ -2758,7 +2759,6 @@ loop_again:
*/
zone_clear_flag(zone, ZONE_CONGESTED);
}
-
}
/*
@@ -2776,17 +2776,6 @@ loop_again:
}
/*
- * OK, kswapd is getting into trouble. Take a nap, then take
- * another pass across the zones.
- */
- if (total_scanned && (sc.priority < DEF_PRIORITY - 2)) {
- if (has_under_min_watermark_zone)
- count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
- else if (unbalanced_zone)
- wait_iff_congested(unbalanced_zone, BLK_RW_ASYNC, HZ/10);
- }
-
- /*
* We do this so kswapd doesn't build up large priorities for
* example when it is freeing in parallel with allocators. It
* matches the direct reclaim path behaviour in terms of impact
--
1.8.1
--
Zlatko
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