background
========================================
current VM implementation doesn't has limit of # of parallel reclaim.
when heavy workload, it bring to 2 bad things
- heavy lock contention
- unnecessary swap out
abount 2 month ago, KAMEZA Hiroyuki proposed the patch of page
reclaim throttle and explain it improve reclaim time.
http://marc.info/?l=linux-mm&m=119667465917215&w=2
but unfortunately it works only memcgroup reclaim.
Today, I implement it again for support global reclaim and mesure it.
test machine, method and result
==================================================
<test machine>
CPU: IA64 x8
MEM: 8GB
SWAP: 2GB
<test method>
got hackbench from
http://people.redhat.com/mingo/cfs-scheduler/tools/hackbench.c
$ /usr/bin/time hackbench 120 process 1000
this parameter mean consume all physical memory and
1GB swap space on my test environment.
<test result (average of 3 times measurement)>
before:
hackbench result: 282.30
/usr/bin/time result
user: 14.16
sys: 1248.47
elapse: 432.93
major fault: 29026
max parallel reclaim tasks: 1298
max consumption time of
try_to_free_pages(): 70394
after:
hackbench result: 30.36
/usr/bin/time result
user: 14.26
sys: 294.44
elapse: 118.01
major fault: 3064
max parallel reclaim tasks: 4
max consumption time of
try_to_free_pages(): 12234
conclusion
=========================================
this patch improve 3 things.
1. reduce unnecessary swap
(see above major fault. about 90% reduced)
2. improve throughput performance
(see above hackbench result. about 90% reduced)
3. improve interactive performance.
(see above max consumption of try_to_free_pages.
about 80% reduced)
4. reduce lock contention.
(see above sys time. about 80% reduced)
Now, we got about 1000% performance improvement of hackbench :)
foture works
==========================================================
- more discussion with memory controller guys.
Signed-off-by: KOSAKI Motohiro <[EMAIL PROTECTED]>
CC: KAMEZAWA Hiroyuki <[EMAIL PROTECTED]>
CC: Balbir Singh <[EMAIL PROTECTED]>
CC: Rik van Riel <[EMAIL PROTECTED]>
CC: Lee Schermerhorn <[EMAIL PROTECTED]>
---
include/linux/nodemask.h | 1
mm/vmscan.c | 49 +++++++++++++++++++++++++++++++++++++++++++++--
2 files changed, 48 insertions(+), 2 deletions(-)
Index: b/include/linux/nodemask.h
===================================================================
--- a/include/linux/nodemask.h 2008-02-19 13:58:05.000000000 +0900
+++ b/include/linux/nodemask.h 2008-02-19 13:58:23.000000000 +0900
@@ -431,6 +431,7 @@ static inline int num_node_state(enum no
#define num_online_nodes() num_node_state(N_ONLINE)
#define num_possible_nodes() num_node_state(N_POSSIBLE)
+#define num_highmem_nodes() num_node_state(N_HIGH_MEMORY)
#define node_online(node) node_state((node), N_ONLINE)
#define node_possible(node) node_state((node), N_POSSIBLE)
Index: b/mm/vmscan.c
===================================================================
--- a/mm/vmscan.c 2008-02-19 13:58:05.000000000 +0900
+++ b/mm/vmscan.c 2008-02-19 14:04:06.000000000 +0900
@@ -127,6 +127,11 @@ long vm_total_pages; /* The total number
static LIST_HEAD(shrinker_list);
static DECLARE_RWSEM(shrinker_rwsem);
+static atomic_t nr_reclaimers = ATOMIC_INIT(0);
+static DECLARE_WAIT_QUEUE_HEAD(reclaim_throttle_waitq);
+#define RECLAIM_LIMIT (2 * num_highmem_nodes())
+
+
#ifdef CONFIG_CGROUP_MEM_CONT
#define scan_global_lru(sc) (!(sc)->mem_cgroup)
#else
@@ -1421,6 +1426,46 @@ out:
return ret;
}
+static unsigned long try_to_free_pages_throttled(struct zone **zones,
+ int order,
+ gfp_t gfp_mask,
+ struct scan_control *sc)
+{
+ unsigned long nr_reclaimed = 0;
+ unsigned long start_time;
+ int i;
+
+ start_time = jiffies;
+
+ wait_event(reclaim_throttle_waitq,
+ atomic_add_unless(&nr_reclaimers, 1, RECLAIM_LIMIT));
+
+ /* more reclaim until needed? */
+ if (unlikely(time_after(jiffies, start_time + HZ))) {
+ for (i = 0; zones[i] != NULL; i++) {
+ struct zone *zone = zones[i];
+ int classzone_idx = zone_idx(zones[0]);
+
+ if (!populated_zone(zone))
+ continue;
+
+ if (zone_watermark_ok(zone, order, 4*zone->pages_high,
+ classzone_idx, 0)) {
+ nr_reclaimed = 1;
+ goto out;
+ }
+ }
+ }
+
+ nr_reclaimed = do_try_to_free_pages(zones, gfp_mask, sc);
+
+out:
+ atomic_dec(&nr_reclaimers);
+ wake_up_all(&reclaim_throttle_waitq);
+
+ return nr_reclaimed;
+}
+
unsigned long try_to_free_pages(struct zone **zones, int order, gfp_t gfp_mask)
{
struct scan_control sc = {
@@ -1434,7 +1479,7 @@ unsigned long try_to_free_pages(struct z
.isolate_pages = isolate_pages_global,
};
- return do_try_to_free_pages(zones, gfp_mask, &sc);
+ return try_to_free_pages_throttled(zones, order, gfp_mask, &sc);
}
#ifdef CONFIG_CGROUP_MEM_CONT
@@ -1456,7 +1501,7 @@ unsigned long try_to_free_mem_cgroup_pag
int target_zone = gfp_zone(GFP_HIGHUSER_MOVABLE);
zones = NODE_DATA(numa_node_id())->node_zonelists[target_zone].zones;
- if (do_try_to_free_pages(zones, sc.gfp_mask, &sc))
+ if (try_to_free_pages_throttled(zones, 0, sc.gfp_mask, &sc))
return 1;
return 0;
}
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