w.r.t:
> 1) direct reclaims occurring quite frequently, resulting in delayed
> file read requests
> 2) direct reclaims falling into congestion_wait() even though no
> congestion at the time, this results in video jitter.
Backporting the following changes seemed to greatly improve these issues:
-vmscan: synchronous lumpy reclaim should not call congestion_wait()
-writeback: do not sleep on the congestion queue if there are no
congested BDIs or if significant congestion is not being encountered
in the current zone
-vmscan: avoid setting zone congested if no page dirty
w.r.t.:
> 3) kswapd not reclaiming pages quickly enough due to falling into
> congestion_wait() very often. (or stays in congestion_wait() for too long)
The attached patch takes an idea from Mel Gorman's patch for
"writeback: do not sleep on the congestion queue if there are no
congested BDIs or if significant congestion is not being encountered
in the current zone" and applies it around the congestion_wait() in
balance_pgdat(). The idea is that if there is no congestion then avoid
potentially wait for too long. Comments or alternate solutions would
be appreciated.
Thanks,
Jeff Vanhoof
commit af8ebaca0d367e14b49a151731e8a3e9bc6685f1
Author: Jeff Vanhoof <jdv1029@xxxxxxxxx>
Date: Tue Aug 16 00:14:31 2011 -0500
linux-mm: Improve kswapd reclaimation of memory
This is a workaround to improve the number of pages reclaimed
in kswapd so that direct reclaims and iowaits are minimized.
Change-Id: I491e9c80809b5ec3e1e7807742807a2317fc2394
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index fa79632..e5b6d3d 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -286,6 +286,7 @@ void clear_bdi_congested(struct backing_dev_info *bdi, int sync);
void set_bdi_congested(struct backing_dev_info *bdi, int sync);
long congestion_wait(int sync, long timeout);
long wait_iff_congested(struct zone *zone, int sync, long timeout);
+int query_iff_congested(struct zone *zone, int sync);
static inline bool bdi_cap_writeback_dirty(struct backing_dev_info *bdi)
{
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 4254946..fcf7976 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -850,3 +850,32 @@ out:
return ret;
}
EXPORT_SYMBOL(wait_iff_congested);
+
+/**
+ * query_iff_congested - Checks if a backing_dev (any backing_dev) is
+ * congested or if the given @zone has has experienced recent congestion.
+ * @zone: A zone to check if it is heavily congested
+ * @sync: SYNC or ASYNC IO
+ *
+ * The return value is 1 if either backing_dev (any) or @zone is congested,
+ * otherwise 0 is returned.
+ *
+ */
+int query_iff_congested(struct zone *zone, int sync)
+{
+ long ret = 1;
+ DEFINE_WAIT(wait);
+ wait_queue_head_t *wqh = &congestion_wqh[sync];
+
+ /*
+ * If there is no congestion, or heavy congestion is not being
+ * encountered in the current zone, set ret to 0
+ */
+ if (atomic_read(&nr_bdi_congested[sync]) == 0 ||
+ !zone_is_reclaim_congested(zone)) {
+ ret = 0;
+ }
+
+ return ret;
+}
+EXPORT_SYMBOL(query_iff_congested);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 1bd01ee..e8686f0 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2169,6 +2169,7 @@ loop_again:
int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
unsigned long lru_pages = 0;
int has_under_min_watermark_zone = 0;
+ int any_zone_congested = 0;
/* The swap token gets in the way of swapout... */
if (!priority)
@@ -2294,6 +2295,13 @@ loop_again:
}
if (all_zones_ok)
break; /* kswapd: all done */
+
+ /* Check to see if any zones are congested */
+ for (i = pgdat->nr_zones - 1; i >= 0; i--) {
+ struct zone *zone = pgdat->node_zones + i;
+ any_zone_congested |=
+ query_iff_congested(zone, BLK_RW_ASYNC);
+ }
+
/*
* OK, kswapd is getting into trouble. Take a nap, then take
* another pass across the zones.
@@ -2301,6 +2309,9 @@ loop_again:
if (total_scanned && (priority < DEF_PRIORITY - 2)) {
if (has_under_min_watermark_zone)
count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
+ else if (!any_zone_congested &&
+ (priority > DEF_PRIORITY - 8))
+ congestion_wait(BLK_RW_ASYNC, HZ/50);
else
congestion_wait(BLK_RW_ASYNC, HZ/10);
}