Re: Free memory never fully used, swapping
From: KOSAKI Motohiro
Date: Thu Nov 25 2010 - 05:51:53 EST
> kswapd is throwing out many times what is needed for the order 3
> watermark to be met. It seems to be not as bad now, but look at these
> pages being reclaimed (200ms intervals, whitespace-packed buddyinfo
> followed by nr_pages_free calculation and final order-3 watermark test,
> kswapd woken after the second sample):
>
> Normal zone at the same time (shown separately for clarity):
>
> Zone order:0 1 2 3 4 5 6 7 8 9 A nr_free or3-low-chk
>
> Normal 452 1 0 0 0 0 0 0 0 0 0 454 -5 <= 238
> Normal 452 1 0 0 0 0 0 0 0 0 0 454 -5 <= 238
> (kswapd wakes)
> Normal 7618 76 0 0 0 0 0 0 0 0 0 7770 145 <= 238
> Normal 8860 73 1 0 0 0 0 0 0 0 0 9010 143 <= 238
> Normal 8929 25 0 0 0 0 0 0 0 0 0 8979 43 <= 238
> Normal 8917 0 0 0 0 0 0 0 0 0 0 8917 -7 <= 238
> Normal 8978 16 0 0 0 0 0 0 0 0 0 9010 25 <= 238
> Normal 9064 4 0 0 0 0 0 0 0 0 0 9072 1 <= 238
> Normal 9068 2 0 0 0 0 0 0 0 0 0 9072 -3 <= 238
> Normal 8992 9 0 0 0 0 0 0 0 0 0 9010 11 <= 238
> Normal 9060 6 0 0 0 0 0 0 0 0 0 9072 5 <= 238
> Normal 9010 0 0 0 0 0 0 0 0 0 0 9010 -7 <= 238
> Normal 8907 5 0 0 0 0 0 0 0 0 0 8917 3 <= 238
> Normal 8576 0 0 0 0 0 0 0 0 0 0 8576 -7 <= 238
> Normal 8018 0 0 0 0 0 0 0 0 0 0 8018 -7 <= 238
> Normal 6778 0 0 0 0 0 0 0 0 0 0 6778 -7 <= 238
> Normal 6189 0 0 0 0 0 0 0 0 0 0 6189 -7 <= 238
> Normal 6220 0 0 0 0 0 0 0 0 0 0 6220 -7 <= 238
> Normal 6096 0 0 0 0 0 0 0 0 0 0 6096 -7 <= 238
> Normal 6251 0 0 0 0 0 0 0 0 0 0 6251 -7 <= 238
> Normal 6127 0 0 0 0 0 0 0 0 0 0 6127 -7 <= 238
> Normal 6218 1 0 0 0 0 0 0 0 0 0 6220 -5 <= 238
> Normal 6034 0 0 0 0 0 0 0 0 0 0 6034 -7 <= 238
> Normal 6065 0 0 0 0 0 0 0 0 0 0 6065 -7 <= 238
> Normal 6189 0 0 0 0 0 0 0 0 0 0 6189 -7 <= 238
> Normal 6189 0 0 0 0 0 0 0 0 0 0 6189 -7 <= 238
> Normal 6096 0 0 0 0 0 0 0 0 0 0 6096 -7 <= 238
> Normal 6127 0 0 0 0 0 0 0 0 0 0 6127 -7 <= 238
> Normal 6158 0 0 0 0 0 0 0 0 0 0 6158 -7 <= 238
> Normal 6127 0 0 0 0 0 0 0 0 0 0 6127 -7 <= 238
> (kswapd sleeps -- maybe too much turkey)
>
> DMA32 get so much reclaimed that the watermark test succeeded long ago.
> Meanwhile, Normal is being reclaimed as well, but because it's fighting
> with allocations, it tries for a while and eventually succeeds (I think),
> but the 200ms samples didn't catch it.
>
> KOSAKI Motohiro, I'm interested in your commit 73ce02e9. This seems
> to be similar to this problem, but your change is not working here.
> We're seeing kswapd run without sleeping, KSWAPD_SKIP_CONGESTION_WAIT
> is increasing (so has_under_min_watermark_zone is true), and pageoutrun
> increasing all the time. This means that balance_pgdat() keeps being
> called, but sleeping_prematurely() is returning true, so kswapd() just
> keeps re-calling balance_pgdat(). If your approach is correct to stop
> kswapd here, the problem seems to be that balance_pgdat's copy of order
> and sc.order is being set to 0, but not pgdat->kswapd_max_order, so
> kswapd never really sleeps. How is this supposed to work?
Um. this seems regression since commit f50de2d381 (vmscan: have kswapd sleep
for a short interval and double check it should be asleep)
Can you please try this?
Subject: [PATCH] vmscan: don't rewakeup kswapd if zone memory was exhaust
---
mm/vmscan.c | 18 +++++++++++-------
1 files changed, 11 insertions(+), 7 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 1fcadaf..2945c74 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2148,7 +2148,7 @@ static int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
* For kswapd, balance_pgdat() will work across all this node's zones until
* they are all at high_wmark_pages(zone).
*
- * Returns the number of pages which were actually freed.
+ * Return 1 if balancing was suceeded, otherwise 0.
*
* There is special handling here for zones which are full of pinned pages.
* This can happen if the pages are all mlocked, or if they are all used by
@@ -2165,7 +2165,7 @@ static int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
* interoperates with the page allocator fallback scheme to ensure that aging
* of pages is balanced across the zones.
*/
-static unsigned long balance_pgdat(pg_data_t *pgdat, int order)
+static int balance_pgdat(pg_data_t *pgdat, int order)
{
int all_zones_ok;
int priority;
@@ -2361,10 +2361,10 @@ out:
goto loop_again;
}
- return sc.nr_reclaimed;
+ return (sc.nr_reclaimed >= SWAP_CLUSTER_MAX);
}
-static void kswapd_try_to_sleep(pg_data_t *pgdat, int order)
+static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int force)
{
long remaining = 0;
DEFINE_WAIT(wait);
@@ -2374,6 +2374,9 @@ static void kswapd_try_to_sleep(pg_data_t *pgdat, int order)
prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
+ if (force)
+ goto sleep:
+
/* Try to sleep for a short interval */
if (!sleeping_prematurely(pgdat, order, remaining)) {
remaining = schedule_timeout(HZ/10);
@@ -2386,6 +2389,7 @@ static void kswapd_try_to_sleep(pg_data_t *pgdat, int order)
* go fully to sleep until explicitly woken up.
*/
if (!sleeping_prematurely(pgdat, order, remaining)) {
+ sleep:
trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
/*
@@ -2426,11 +2430,11 @@ static int kswapd(void *p)
unsigned long order;
pg_data_t *pgdat = (pg_data_t*)p;
struct task_struct *tsk = current;
-
struct reclaim_state reclaim_state = {
.reclaimed_slab = 0,
};
const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
+ int balanced = 0;
lockdep_set_current_reclaim_state(GFP_KERNEL);
@@ -2467,7 +2471,7 @@ static int kswapd(void *p)
*/
order = new_order;
} else {
- kswapd_try_to_sleep(pgdat, order);
+ kswapd_try_to_sleep(pgdat, order, !balanced);
order = pgdat->kswapd_max_order;
}
@@ -2481,7 +2485,7 @@ static int kswapd(void *p)
*/
if (!ret) {
trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
- balance_pgdat(pgdat, order);
+ balanced = balance_pgdat(pgdat, order);
}
}
return 0;
--
1.6.5.2
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