[PATCH 2/2] vmscan: kill shrink_all_zones()
From: KOSAKI Motohiro
Date: Fri Oct 09 2009 - 04:57:43 EST
shrink_all_zone() was introduced by commit d6277db4ab (swsusp: rework
memory shrinker) for hibernate performance improvement. and sc.swap_cluster_max
was introduced by commit a06fe4d307 (Speed freeing memory for suspend).
commit a06fe4d307 said
Without the patch:
Freed 14600 pages in 1749 jiffies = 32.61 MB/s (Anomolous!)
Freed 88563 pages in 14719 jiffies = 23.50 MB/s
Freed 205734 pages in 32389 jiffies = 24.81 MB/s
With the patch:
Freed 68252 pages in 496 jiffies = 537.52 MB/s
Freed 116464 pages in 569 jiffies = 798.54 MB/s
Freed 209699 pages in 705 jiffies = 1161.89 MB/s
At that time, their patch was pretty worth. However, Modern Hardware
trend and recent VM improvement broke its worth. From several reason,
I think we should remove shrink_all_zones() at all.
detail:
1) Old days, shrink_zone()'s slowness was mainly caused by stupid congestion_wait()
at no i/o congestion.
but current shrink_zone() is sane, not slow.
2) shrink_all_zone() try to shrink all pages at a time. but it doesn't works
fine on numa system.
example)
System has 4GB memory and each node have 2GB. and hibernate need 1GB.
optimal)
steal 500MB from each node.
shrink_all_zones)
steal 1GB from node-0.
Oh, Cache balancing was broke ;)
Unfortunately, Desktop system moved ahead NUMA.
(Side note, if hibernate require 2GB, shrink_all_zones() never success)
3) if the node has several I/O flighting pages, shrink_all_zones() makes
pretty bad result.
schenario) hibernate need 1GB
1) shrink_all_zones() try to reclaim 1GB from Node-0
2) but it only reclaimed 990MB
3) stupidly, shrink_all_zones() try to reclaim 1GB from Node-1
4) it reclaimed 990MB
Oh, well. it reclaimed twice much than required.
In the other hand, current shrink_zone() has sane baling out logic.
then, it doesn't make overkill reclaim. then, we lost shrink_zones()'s risk.
4) SplitLRU VM always keep active/inactive ratio very carefully. inactive list only
shrinking break its assumption. it makes unnecessary OOM risk. it obviously suboptimal.
Throuput comparision
==============================================
old 2192.10 MB/s
new 2222.22 MB/s
ok, it's almost same throuput.
Cc: Rafael J. Wysocki <rjw@xxxxxxx>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
---
mm/vmscan.c | 75 +++++++++++++---------------------------------------------
1 files changed, 17 insertions(+), 58 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 80e727d..9f28166 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2130,51 +2130,6 @@ unsigned long global_lru_pages(void)
#ifdef CONFIG_HIBERNATION
/*
- * Helper function for shrink_all_memory(). Tries to reclaim 'nr_pages' pages
- * from LRU lists system-wide, for given pass and priority.
- *
- * For pass > 3 we also try to shrink the LRU lists that contain a few pages
- */
-static void shrink_all_zones(unsigned long nr_pages, int prio,
- int pass, struct scan_control *sc)
-{
- struct zone *zone;
- unsigned long nr_reclaimed = 0;
-
- for_each_populated_zone(zone) {
- enum lru_list l;
-
- if (zone_is_all_unreclaimable(zone) && prio != DEF_PRIORITY)
- continue;
-
- for_each_evictable_lru(l) {
- enum zone_stat_item ls = NR_LRU_BASE + l;
- unsigned long lru_pages = zone_page_state(zone, ls);
-
- /* For pass = 0, we don't shrink the active list */
- if (pass == 0 && (l == LRU_ACTIVE_ANON ||
- l == LRU_ACTIVE_FILE))
- continue;
-
- zone->lru[l].nr_saved_scan += (lru_pages >> prio) + 1;
- if (zone->lru[l].nr_saved_scan >= nr_pages || pass > 3) {
- unsigned long nr_to_scan;
-
- zone->lru[l].nr_saved_scan = 0;
- nr_to_scan = min(nr_pages, lru_pages);
- nr_reclaimed += shrink_list(l, nr_to_scan, zone,
- sc, prio);
- if (nr_reclaimed >= nr_pages) {
- sc->nr_reclaimed += nr_reclaimed;
- return;
- }
- }
- }
- }
- sc->nr_reclaimed += nr_reclaimed;
-}
-
-/*
* Try to free `nr_pages' of memory, system-wide, and return the number of
* freed pages.
*
@@ -2188,12 +2143,18 @@ unsigned long shrink_all_memory(unsigned long nr_pages)
int pass;
struct reclaim_state reclaim_state;
struct scan_control sc = {
- .gfp_mask = GFP_KERNEL,
+ .gfp_mask = GFP_HIGHUSER_MOVABLE,
+ .may_swap = 0,
.may_unmap = 0,
.may_writepage = 1,
+ .swap_cluster_max = SWAP_CLUSTER_MAX,
+ .nr_to_reclaim = nr_pages,
+ .swappiness = vm_swappiness,
+ .order = 0,
.isolate_pages = isolate_pages_global,
- .nr_reclaimed = 0,
};
+ struct zonelist * zonelist = node_zonelist(first_online_node,
+ GFP_HIGHUSER_MOVABLE);
current->reclaim_state = &reclaim_state;
@@ -2215,9 +2176,9 @@ unsigned long shrink_all_memory(unsigned long nr_pages)
/*
* We try to shrink LRUs in 5 passes:
- * 0 = Reclaim from inactive_list only
- * 1 = Reclaim from active list but don't reclaim mapped
- * 2 = 2nd pass of type 1
+ * 0 = Reclaim unmapped pages
+ * 1 = 2nd pass of type 0
+ * 2 = 3rd pass of type 0
* 3 = Reclaim mapped (normal reclaim)
* 4 = 2nd pass of type 3
*/
@@ -2225,15 +2186,15 @@ unsigned long shrink_all_memory(unsigned long nr_pages)
int prio;
/* Force reclaiming mapped pages in the passes #3 and #4 */
- if (pass > 2)
+ if (pass > 2) {
sc.may_unmap = 1;
+ sc.may_swap = 1;
+ }
for (prio = DEF_PRIORITY; prio >= 0; prio--) {
- unsigned long nr_to_scan = nr_pages - sc.nr_reclaimed;
-
sc.nr_scanned = 0;
- sc.swap_cluster_max = nr_to_scan;
- shrink_all_zones(nr_to_scan, prio, pass, &sc);
+
+ shrink_zones(prio, zonelist, &sc);
if (sc.nr_reclaimed >= nr_pages)
goto out;
@@ -2243,10 +2204,8 @@ unsigned long shrink_all_memory(unsigned long nr_pages)
sc.nr_reclaimed += reclaim_state.reclaimed_slab;
if (sc.nr_reclaimed >= nr_pages)
goto out;
-
- if (sc.nr_scanned && prio < DEF_PRIORITY - 2)
- congestion_wait(BLK_RW_ASYNC, HZ / 10);
}
+ congestion_wait(BLK_RW_ASYNC, HZ / 10);
}
/*
--
1.6.2.5
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