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[Xen-devel] [PATCH 2/2] blkback: Add a module parameter for aggressive pool shrinking duration

From: SeongJae Park <sjpark@xxxxxxxxx>

As discussed by the previous commit ("xen/blkback: Aggressively shrink
page pools if a memory pressure is detected"), the aggressive pool
shrinking duration should be carefully selected:
``If it is too long, free pages pool shrinking overhead can reduce the
I/O performance.  If it is too short, blkback will not free enough pages
to reduce the memory pressure.``

That said, the proper duration would depends on given configurations and
workloads.  For the reason, this commit allows users to set it via a
module parameter interface.

Signed-off-by: SeongJae Park <sjpark@xxxxxxxxx>
Suggested-by: Amit Shah <aams@xxxxxxxxx>
 drivers/block/xen-blkback/blkback.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/block/xen-blkback/blkback.c 
index aa1a127093e5..88c011300ee9 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -137,9 +137,13 @@ module_param(log_stats, int, 0644);
  * Once a memory pressure is detected, keep aggressive shrinking of the free
- * page pools for this time (msec)
+ * page pools for this time (milliseconds)
+static int xen_blkif_aggressive_shrinking_duration = 1;
+               xen_blkif_aggressive_shrinking_duration, int, 0644);
+"Duration to do aggressive shrinking when a memory pressure is detected");
 static unsigned long xen_blk_mem_pressure_end;
@@ -147,7 +151,7 @@ static unsigned long blkif_shrink_count(struct shrinker 
                                struct shrink_control *sc)
        xen_blk_mem_pressure_end = jiffies +
-               msecs_to_jiffies(AGGRESSIVE_SHRINKING_DURATION);
+               msecs_to_jiffies(xen_blkif_aggressive_shrinking_duration);
        return 0;

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