On Wed 22-02-17 17:04:48, Jia He wrote:Yes, at last the allocated hugepages are less than 4000
When I try to dynamically allocate the hugepages more than system total
free memory:
e.g. echo 4000 >/proc/sys/vm/nr_hugepages
I assume that the command has terminated with less huge pages allocated
than requested but
agree.Node 3, zone DMA[...]
pages free 2951
min 2821
low 3526
high 4231
it left the zone below high watermark with
node_scanned 0
spanned 245760
present 245760
managed 245388
nr_free_pages 2951
nr_zone_inactive_anon 0
nr_zone_active_anon 0
nr_zone_inactive_file 0
nr_zone_active_file 0
no pages reclaimable, so kswapd will not go to sleep. It would be quite
easy and comfortable to call it a misconfiguration but it seems that
it might be quite easy to hit with NUMA machines which have large
differences in the node sizes. I guess it makes sense to back off
the kswapd rather than burning CPU without any way to make forward
progress.
Yes, even in the bad case, when kswapd takes all the cpu, the reclaimable
[...]
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 532a2a7..a05e3ab 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3139,7 +3139,8 @@ static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, int classzone_idx)
if (!managed_zone(zone))
continue;
- if (!zone_balanced(zone, order, classzone_idx))
+ if (!zone_balanced(zone, order, classzone_idx)
+ && zone_reclaimable_pages(zone))
return false;
OK, this makes some sense, although zone_reclaimable_pages doesn't count
SLAB reclaimable pages. So we might go to sleep with a reclaimable slab
still around. This is not really easy to address because the reclaimable
slab doesn't really imply that those pages will be reclaimed...
I mean, if any one zone has reclaimable pages, then this zone's *node* has
}
@@ -3502,6 +3503,7 @@ void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
{
pg_data_t *pgdat;
int z;
+ int node_has_relaimable_pages = 0;
if (!managed_zone(zone))
return;
@@ -3522,8 +3524,15 @@ void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
if (zone_balanced(zone, order, classzone_idx))
return;
+
+ if (!zone_reclaimable_pages(zone))
+ node_has_relaimable_pages = 1;
What, this doesn't make any sense? Did you mean if (zone_reclaimable_pages)?
}
+ /* Dont wake kswapd if no reclaimable pages */
+ if (!node_has_relaimable_pages)
+ return;
+
trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
wake_up_interruptible(&pgdat->kswapd_wait);
}
--
1.8.5.6
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