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Subject[-mm][PATCH 4/5] core of reclaim throttle
add throttle to shrink_zone() for performance improvement and prevent incorrect oom.


Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>

---
include/linux/mmzone.h | 2 +
include/linux/sched.h | 1
mm/Kconfig | 10 +++++++++
mm/page_alloc.c | 4 +++
mm/vmscan.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++-
5 files changed, 68 insertions(+), 1 deletion(-)
Index: b/include/linux/mmzone.h
===================================================================
--- a/include/linux/mmzone.h 2008-05-03 00:39:44.000000000 +0900
+++ b/include/linux/mmzone.h 2008-05-03 00:44:12.000000000 +0900
@@ -328,6 +328,8 @@ struct zone {
unsigned long spanned_pages; /* total size, including holes */
unsigned long present_pages; /* amount of memory (excluding holes) */

+ atomic_t nr_reclaimers;
+ wait_queue_head_t reclaim_throttle_waitq;
/*
* rarely used fields:
*/
Index: b/mm/page_alloc.c
===================================================================
--- a/mm/page_alloc.c 2008-05-03 00:39:44.000000000 +0900
+++ b/mm/page_alloc.c 2008-05-03 00:44:12.000000000 +0900
@@ -3502,6 +3502,10 @@ static void __paginginit free_area_init_
zone->nr_scan_inactive = 0;
zap_zone_vm_stats(zone);
zone->flags = 0;
+
+ zone->nr_reclaimers = ATOMIC_INIT(0);
+ init_waitqueue_head(&zone->reclaim_throttle_waitq);
+
if (!size)
continue;

Index: b/mm/vmscan.c
===================================================================
--- a/mm/vmscan.c 2008-05-03 00:43:48.000000000 +0900
+++ b/mm/vmscan.c 2008-05-04 20:56:01.000000000 +0900
@@ -74,6 +74,11 @@ struct scan_control {

int order;

+ /* Can shrink be cutted off if other task freeded enough page. */
+ int may_cut_off;
+
+ unsigned long was_freed;
+
/* Which cgroup do we reclaim from */
struct mem_cgroup *mem_cgroup;

@@ -120,6 +125,7 @@ struct scan_control {
int vm_swappiness = 60;
long vm_total_pages; /* The total number of pages which the VM controls */

+#define MAX_RECLAIM_TASKS CONFIG_NR_MAX_RECLAIM_TASKS_PER_ZONE
static LIST_HEAD(shrinker_list);
static DECLARE_RWSEM(shrinker_rwsem);

@@ -1187,7 +1193,42 @@ static int shrink_zone(int priority, str
unsigned long nr_inactive;
unsigned long nr_to_scan;
unsigned long nr_reclaimed = 0;
+ int ret = 0;
+ int throttle_on = 0;
+ unsigned long freed;
+
+ /* avoid recursing wait_evnet */
+ if (current->flags & PF_RECLAIMING)
+ goto shrinking;
+
+ throttle_on = 1;
+ current->flags |= PF_RECLAIMING;
+ wait_event(zone->reclaim_throttle_waitq,
+ atomic_add_unless(&zone->nr_reclaimers, 1, MAX_RECLAIM_TASKS));
+
+ /* in some situation (e.g. hibernation), shrink processing shouldn't be
+ cut off even though large memory freeded. */
+ if (!sc->may_cut_off)
+ goto shrinking;
+
+ /* kswapd is no related for user latency experience. */
+ if (current->flags & PF_KSWAPD)
+ goto shrinking;
+
+ /* reclaim still necessary? */
+ freed = get_vm_event(PGFREE);
+ if (scan_global_lru(sc) &&
+ ((freed - sc->was_freed) >= (zone->pages_high*4))) {
+ sc->was_freed = freed;
+
+ if (zone_watermark_ok(zone, sc->order, zone->pages_high,
+ gfp_zone(sc->gfp_mask), 0)) {
+ ret = -EAGAIN;
+ goto out;
+ }
+ }

+shrinking:
if (scan_global_lru(sc)) {
/*
* Add one to nr_to_scan just to make sure that the kernel
@@ -1239,9 +1280,16 @@ static int shrink_zone(int priority, str
}
}

+out:
+ if (throttle_on) {
+ current->flags &= ~PF_RECLAIMING;
+ atomic_dec(&zone->nr_reclaimers);
+ wake_up(&zone->reclaim_throttle_waitq);
+ }
+
sc->nr_reclaimed += nr_reclaimed;
throttle_vm_writeout(sc->gfp_mask);
- return 0;
+ return ret;
}

/*
@@ -1438,6 +1486,8 @@ unsigned long try_to_free_pages(struct z
.order = order,
.mem_cgroup = NULL,
.isolate_pages = isolate_pages_global,
+ .may_cut_off = 1,
+ .was_freed = get_vm_event(PGFREE),
};

return do_try_to_free_pages(zonelist, &sc);
Index: b/mm/Kconfig
===================================================================
--- a/mm/Kconfig 2008-05-03 00:39:44.000000000 +0900
+++ b/mm/Kconfig 2008-05-03 00:44:12.000000000 +0900
@@ -205,3 +205,13 @@ config NR_QUICK
config VIRT_TO_BUS
def_bool y
depends on !ARCH_NO_VIRT_TO_BUS
+
+config NR_MAX_RECLAIM_TASKS_PER_ZONE
+ int "maximum number of reclaiming tasks at the same time"
+ default 3
+ help
+ This value determines the number of threads which can do page reclaim
+ in a zone simultaneously. If this is too big, performance under heavy memory
+ pressure will decrease.
+ If unsure, use default.
+
Index: b/include/linux/sched.h
===================================================================
--- a/include/linux/sched.h 2008-05-03 00:39:44.000000000 +0900
+++ b/include/linux/sched.h 2008-05-03 00:44:12.000000000 +0900
@@ -1484,6 +1484,7 @@ static inline void put_task_struct(struc
#define PF_MEMPOLICY 0x10000000 /* Non-default NUMA mempolicy */
#define PF_MUTEX_TESTER 0x20000000 /* Thread belongs to the rt mutex tester */
#define PF_FREEZER_SKIP 0x40000000 /* Freezer should not count it as freezeable */
+#define PF_RECLAIMING 0x80000000 /* The task have page reclaim throttling ticket */

/*
* Only the _current_ task can read/write to tsk->flags, but other



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