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authorMel Gorman <mgorman@suse.de>2011-07-08 15:39:40 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-07-08 21:14:43 -0700
commit215ddd6664ced067afca7eebd2d1eb83f064ff5a (patch)
treeb0e01235355d9c77b3bf63e0a57a6721fc8e3793
parentda175d06b437093f93109ba9e5efbe44dfdf9409 (diff)
downloadlinux-linaro-215ddd6664ced067afca7eebd2d1eb83f064ff5a.tar.gz
mm: vmscan: only read new_classzone_idx from pgdat when reclaiming successfully
During allocator-intensive workloads, kswapd will be woken frequently causing free memory to oscillate between the high and min watermark. This is expected behaviour. Unfortunately, if the highest zone is small, a problem occurs. When balance_pgdat() returns, it may be at a lower classzone_idx than it started because the highest zone was unreclaimable. Before checking if it should go to sleep though, it checks pgdat->classzone_idx which when there is no other activity will be MAX_NR_ZONES-1. It interprets this as it has been woken up while reclaiming, skips scheduling and reclaims again. As there is no useful reclaim work to do, it enters into a loop of shrinking slab consuming loads of CPU until the highest zone becomes reclaimable for a long period of time. There are two problems here. 1) If the returned classzone or order is lower, it'll continue reclaiming without scheduling. 2) if the highest zone was marked unreclaimable but balance_pgdat() returns immediately at DEF_PRIORITY, the new lower classzone is not communicated back to kswapd() for sleeping. This patch does two things that are related. If the end_zone is unreclaimable, this information is communicated back. Second, if the classzone or order was reduced due to failing to reclaim, new information is not read from pgdat and instead an attempt is made to go to sleep. Due to this, it is also necessary that pgdat->classzone_idx be initialised each time to pgdat->nr_zones - 1 to avoid re-reads being interpreted as wakeups. Signed-off-by: Mel Gorman <mgorman@suse.de> Reported-by: Pádraig Brady <P@draigBrady.com> Tested-by: Pádraig Brady <P@draigBrady.com> Tested-by: Andrew Lutomirski <luto@mit.edu> Acked-by: Rik van Riel <riel@redhat.com> Cc: Minchan Kim <minchan.kim@gmail.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: <stable@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/vmscan.c34
1 files changed, 21 insertions, 13 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c
index a51b3c9f05b..5ed24b94c5e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2451,7 +2451,6 @@ loop_again:
if (!zone_watermark_ok_safe(zone, order,
high_wmark_pages(zone), 0, 0)) {
end_zone = i;
- *classzone_idx = i;
break;
}
}
@@ -2531,8 +2530,11 @@ loop_again:
total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
sc.may_writepage = 1;
- if (zone->all_unreclaimable)
+ if (zone->all_unreclaimable) {
+ if (end_zone && end_zone == i)
+ end_zone--;
continue;
+ }
if (!zone_watermark_ok_safe(zone, order,
high_wmark_pages(zone), end_zone, 0)) {
@@ -2712,8 +2714,8 @@ static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
*/
static int kswapd(void *p)
{
- unsigned long order;
- int classzone_idx;
+ unsigned long order, new_order;
+ int classzone_idx, new_classzone_idx;
pg_data_t *pgdat = (pg_data_t*)p;
struct task_struct *tsk = current;
@@ -2743,17 +2745,23 @@ static int kswapd(void *p)
tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
set_freezable();
- order = 0;
- classzone_idx = MAX_NR_ZONES - 1;
+ order = new_order = 0;
+ classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
for ( ; ; ) {
- unsigned long new_order;
- int new_classzone_idx;
int ret;
- new_order = pgdat->kswapd_max_order;
- new_classzone_idx = pgdat->classzone_idx;
- pgdat->kswapd_max_order = 0;
- pgdat->classzone_idx = MAX_NR_ZONES - 1;
+ /*
+ * If the last balance_pgdat was unsuccessful it's unlikely a
+ * 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) {
+ new_order = pgdat->kswapd_max_order;
+ new_classzone_idx = pgdat->classzone_idx;
+ pgdat->kswapd_max_order = 0;
+ pgdat->classzone_idx = pgdat->nr_zones - 1;
+ }
+
if (order < new_order || classzone_idx > new_classzone_idx) {
/*
* Don't sleep if someone wants a larger 'order'
@@ -2766,7 +2774,7 @@ static int kswapd(void *p)
order = pgdat->kswapd_max_order;
classzone_idx = pgdat->classzone_idx;
pgdat->kswapd_max_order = 0;
- pgdat->classzone_idx = MAX_NR_ZONES - 1;
+ pgdat->classzone_idx = pgdat->nr_zones - 1;
}
ret = try_to_freeze();