Re: make swappiness safer to use

Fengguang Wu
2007-08-01T01:32:08Z

Here's the updated patch without underflows.

Signed-off-by: Kurt Garloff <garloff@suse.de>
Signed-off-by: Andrea Arcangeli <andrea@suse.de>
Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
---
mm/vmscan.c | 41 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 41 insertions(+)

--- linux-2.6.22-rc6-mm1.orig/mm/vmscan.c
+++ linux-2.6.22-rc6-mm1/mm/vmscan.c
@@ -887,6 +887,7 @@ static void shrink_active_list(unsigned
long mapped_ratio;
long distress;
long swap_tendency;
+ long imbalance;

if (zone_is_near_oom(zone))
goto force_reclaim_mapped;
@@ -922,6 +923,46 @@ static void shrink_active_list(unsigned
swap_tendency = mapped_ratio / 2 + distress + sc->swappiness;

/*
+ * If there's huge imbalance between active and inactive
+ * (think active 100 times larger than inactive) we should
+ * become more permissive, or the system will take too much
+ * cpu before it start swapping during memory pressure.
+ * Distress is about avoiding early-oom, this is about
+ * making swappiness graceful despite setting it to low
+ * values.
+ *
+ * Avoid div by zero with nr_inactive+1, and max resulting
+ * value is vm_total_pages.
+ */
+ imbalance = zone_page_state(zone, NR_ACTIVE);
+ imbalance /= zone_page_state(zone, NR_INACTIVE) + 1;
+
+ /*
+ * Reduce the effect of imbalance if swappiness is low,
+ * this means for a swappiness very low, the imbalance
+ * must be much higher than 100 for this logic to make
+ * the difference.
+ *
+ * Max temporary value is vm_total_pages*100.
+ */
+ imbalance *= (vm_swappiness + 1);
+ imbalance /= 100;
+
+ /*
+ * If not much of the ram is mapped, makes the imbalance
+ * less relevant, it's high priority we refill the inactive
+ * list with mapped pages only in presence of high ratio of
+ * mapped pages.
+ *
+ * Max temporary value is vm_total_pages*100.
+ */
+ imbalance *= mapped_ratio;
+ imbalance /= 100;
+
+ /* apply imbalance feedback to swap_tendency */
+ swap_tendency += imbalance;
+
+ /*
* Now use this metric to decide whether to start moving mapped
* memory onto the inactive list.
*/