From cffa8372f42be4b37931d3cd24b01e837aa123b6 Mon Sep 17 00:00:00 2001 From: Justin Gottula Date: Tue, 12 Mar 2019 15:03:59 -0700 Subject: [PATCH] Fix most zfs_arc_* mod params not actually being modifiable at runtime Most of the zfs_arc_* module parameters do not have their values used by the ARC code directly. Instead, there is a function, arc_tuning_update, which is called during module initialization and periodically thereafter, whose job is to fetch the module parameter values, clamp/ limit them appropriately, and then assign those values to a separate set of internal variables that are actually referenced by the ARC code. Commit 3ec34e55 featured an overhaul of arc_reclaim_thread, which is the former location where the post-init-time calls to arc_tuning_update would occur. The rework split the work previously done by the arc_reclaim_thread into a pair of replacement threads; and unfortunately, the call to arc_tuning_update fell through the cracks and was lost in the reorganization. This meant that changing almost any ARC-related zfs module parameter via /sys/module/zfs/parameters/ would result in the module parameter value itself appearing to change; however the modification would not actually propagate to the ARC code and have any real effect. This commit reinstates the post-init-time call to arc_tuning_update. It is now called during arc_adjust_cb_check; this should be equivalent to its former call location in arc_reclaim_thread. Reviewed-by: Brian Behlendorf Reviewed-by: Tony Hutter Signed-off-by: Justin Gottula Closes #8405 Closes #8463 --- module/zfs/arc.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/module/zfs/arc.c b/module/zfs/arc.c index 9072b6582..637333ed2 100644 --- a/module/zfs/arc.c +++ b/module/zfs/arc.c @@ -5076,6 +5076,14 @@ arc_kmem_reap_soon(void) static boolean_t arc_adjust_cb_check(void *arg, zthr_t *zthr) { + /* + * This is necessary so that any changes which may have been made to + * many of the zfs_arc_* module parameters will be propagated to + * their actual internal variable counterparts. Without this, + * changing those module params at runtime would have no effect. + */ + arc_tuning_update(); + /* * This is necessary in order to keep the kstat information * up to date for tools that display kstat data such as the