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Subject[PATCH] vmscan: improve reclaim throuput to bail out patch
Date
Hi

I evaluate rvr bailout and skip-freeing patch in this week conteniously.
I'd like to dump first output here.



Rik, could you please review following?
==
vmscan bail out patch move nr_reclaimed variable to struct scan_control.
Unfortunately, indirect access can easily happen cache miss.
More unfortunately, Some architecture (e.g. ia64) don't access global
variable so fast.

if heavy memory pressure happend, that's ok.
cache miss already plenty. it is not observable.

but, if memory pressure is lite, performance degression is obserbable.


I compared following three pattern (it was mesured 10 times each)

hackbench 125 process 3000
hackbench 130 process 3000
hackbench 135 process 3000

2.6.28-rc6 bail-out

125 130 135 125 130 135
==============================================================
71.866 75.86 81.274 93.414 73.254 193.382
74.145 78.295 77.27 74.897 75.021 80.17
70.305 77.643 75.855 70.134 77.571 79.896
74.288 73.986 75.955 77.222 78.48 80.619
72.029 79.947 78.312 75.128 82.172 79.708
71.499 77.615 77.042 74.177 76.532 77.306
76.188 74.471 83.562 73.839 72.43 79.833
73.236 75.606 78.743 76.001 76.557 82.726
69.427 77.271 76.691 76.236 79.371 103.189
72.473 76.978 80.643 69.128 78.932 75.736
avg 72.545 76.767 78.534 76.017 77.03 93.256
std 1.89 1.71 2.41 6.29 2.79 34.16
min 69.427 73.986 75.855 69.128 72.43 75.736
max 76.188 79.947 83.562 93.414 82.172 193.382


about 4-5% degression.

Then, this patch introduce temporal local variable.

result:

2.6.28-rc6 this patch

num 125 130 135 125 130 135
==============================================================
71.866 75.86 81.274 67.302 68.269 77.161
74.145 78.295 77.27 72.616 72.712 79.06
70.305 77.643 75.855 72.475 75.712 77.735
74.288 73.986 75.955 69.229 73.062 78.814
72.029 79.947 78.312 71.551 74.392 78.564
71.499 77.615 77.042 69.227 74.31 78.837
76.188 74.471 83.562 70.759 75.256 76.6
73.236 75.606 78.743 69.966 76.001 78.464
69.427 77.271 76.691 69.068 75.218 80.321
72.473 76.978 80.643 72.057 77.151 79.068
avg 72.545 76.767 78.534 70.425 74.2083 78.462
std 1.89 1.71 2.41 1.66 2.34 1.00
min 69.427 73.986 75.855 67.302 68.269 76.6
max 76.188 79.947 83.562 72.616 77.151 80.321


OK. the degression is disappeared.



Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
---
mm/vmscan.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)
Index: b/mm/vmscan.c
===================================================================
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1418,6 +1418,8 @@ static void shrink_zone(int priority, st
unsigned long nr_to_scan;
unsigned long percent[2]; /* anon @ 0; file @ 1 */
enum lru_list l;
+ unsigned long nr_reclaimed = sc->nr_reclaimed;
+ unsigned long swap_cluster_max = sc->swap_cluster_max;

get_scan_ratio(zone, sc, percent);

@@ -1433,7 +1435,7 @@ static void shrink_zone(int priority, st
}
zone->lru[l].nr_scan += scan;
nr[l] = zone->lru[l].nr_scan;
- if (nr[l] >= sc->swap_cluster_max)
+ if (nr[l] >= swap_cluster_max)
zone->lru[l].nr_scan = 0;
else
nr[l] = 0;
@@ -1452,12 +1454,11 @@ static void shrink_zone(int priority, st
nr[LRU_INACTIVE_FILE]) {
for_each_evictable_lru(l) {
if (nr[l]) {
- nr_to_scan = min(nr[l],
- (unsigned long)sc->swap_cluster_max);
+ nr_to_scan = min(nr[l], swap_cluster_max);
nr[l] -= nr_to_scan;

- sc->nr_reclaimed += shrink_list(l, nr_to_scan,
- zone, sc, priority);
+ nr_reclaimed += shrink_list(l, nr_to_scan,
+ zone, sc, priority);
}
}
/*
@@ -1468,11 +1469,13 @@ static void shrink_zone(int priority, st
* with multiple processes reclaiming pages, the total
* freeing target can get unreasonably large.
*/
- if (sc->nr_reclaimed > sc->swap_cluster_max &&
+ if (nr_reclaimed > swap_cluster_max &&
priority < DEF_PRIORITY && !current_is_kswapd())
break;
}

+ sc->nr_reclaimed = nr_reclaimed;
+
/*
* Even if we did not try to evict anon pages at all, we want to
* rebalance the anon lru active/inactive ratio.



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