Obey arc_meta_limit default size when changing arc_max

When decreasing the maximum ARC size preserve the 3/4 default
ratio for the arc_meta_limit.  Otherwise, the arc_meta_limit
may be set the same as arc_max.

Signed-off-by: AndCycle <andcycle@andcycle.idv.tw>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #4001

diff --git a/module/zfs/arc.c b/module/zfs/arc.c
index fa1434e168638b5adfa0ed922ca9f88aa73f5e39..06fb72b602c285b64a0acb8715ab4f78f713591c 100644 (file)
--- a/module/zfs/arc.c
+++ b/module/zfs/arc.c
@@ -5245,7 +5245,7 @@ arc_tuning_update(void)
                arc_c_max = zfs_arc_max;
                arc_c = arc_c_max;
                arc_p = (arc_c >> 1);
-               arc_meta_limit = MIN(arc_meta_limit, arc_c_max);
+               arc_meta_limit = MIN(arc_meta_limit, (3 * arc_c_max) / 4);
        }
 
        /* Valid range: 32M - <arc_c_max> */