The patch titled
kswapd: avoid unnecessary rebalance after an unsuccessful balancing
has been added to the -mm tree. Its filename is
kswapd-avoid-unnecessary-rebalance-after-an-unsuccessful-balancing.patch
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------------------------------------------------------
Subject: kswapd: avoid unnecessary rebalance after an unsuccessful balancing
From: "Alex,Shi" <alex.shi@xxxxxxxxx>
In commit 215ddd66 ("mm: vmscan: only read new_classzone_idx from pgdat
when reclaiming successfully") , Mel Gorman said kswapd is better to sleep
after a unsuccessful balancing if there is tighter reclaim request pending
in the balancing. But in the following scenario, kswapd do something that
is not matched our expectation. The patch fixes this issue.
1, Read pgdat request A (classzone_idx, order = 3)
2, balance_pgdat()
3, During pgdat, a new pgdat request B (classzone_idx, order = 5) is placed
4, balance_pgdat() returns but failed since returned order = 0
5, pgdat of request A assigned to balance_pgdat(), and do balancing again.
While the expectation behavior of kswapd should try to sleep.
Signed-off-by: Alex Shi <alex.shi@xxxxxxxxx>
Reviewed-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxx>
Tested-by: Pádraig Brady <P@xxxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)
diff -puN mm/vmscan.c~kswapd-avoid-unnecessary-rebalance-after-an-unsuccessful-balancing mm/vmscan.c
--- a/mm/vmscan.c~kswapd-avoid-unnecessary-rebalance-after-an-unsuccessful-balancing
+++ a/mm/vmscan.c
@@ -2842,7 +2842,9 @@ static void kswapd_try_to_sleep(pg_data_
static int kswapd(void *p)
{
unsigned long order, new_order;
+ unsigned balanced_order;
int classzone_idx, new_classzone_idx;
+ int balanced_classzone_idx;
pg_data_t *pgdat = (pg_data_t*)p;
struct task_struct *tsk = current;
@@ -2873,7 +2875,9 @@ static int kswapd(void *p)
set_freezable();
order = new_order = 0;
+ balanced_order = 0;
classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
+ balanced_classzone_idx = classzone_idx;
for ( ; ; ) {
int ret;
@@ -2882,7 +2886,8 @@ static int kswapd(void *p)
* new request of a similar or harder type will succeed soon
* so consider going to sleep on the basis we reclaimed at
*/
- if (classzone_idx >= new_classzone_idx && order == new_order) {
+ if (balanced_classzone_idx >= new_classzone_idx &&
+ balanced_order == new_order) {
new_order = pgdat->kswapd_max_order;
new_classzone_idx = pgdat->classzone_idx;
pgdat->kswapd_max_order = 0;
@@ -2897,7 +2902,8 @@ static int kswapd(void *p)
order = new_order;
classzone_idx = new_classzone_idx;
} else {
- kswapd_try_to_sleep(pgdat, order, classzone_idx);
+ kswapd_try_to_sleep(pgdat, balanced_order,
+ balanced_classzone_idx);
order = pgdat->kswapd_max_order;
classzone_idx = pgdat->classzone_idx;
pgdat->kswapd_max_order = 0;
@@ -2914,7 +2920,9 @@ static int kswapd(void *p)
*/
if (!ret) {
trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
- order = balance_pgdat(pgdat, order, &classzone_idx);
+ balanced_classzone_idx = classzone_idx;
+ balanced_order = balance_pgdat(pgdat, order,
+ &balanced_classzone_idx);
}
}
return 0;
_
Patches currently in -mm which might be from alex.shi@xxxxxxxxx are
linux-next.patch
kswapd-avoid-unnecessary-rebalance-after-an-unsuccessful-balancing.patch
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