dm kcopyd: introduce configurable throttling

This patch allows the administrator to reduce the rate at which kcopyd
issues I/O.

Each module that uses kcopyd acquires a throttle parameter that can be
set in /sys/module/*/parameters.

We maintain a history of kcopyd usage by each module in the variables
io_period and total_period in struct dm_kcopyd_throttle. The actual
kcopyd activity is calculated as a percentage of time equal to
"(100 * io_period / total_period)".  This is compared with the user-defined
throttle percentage threshold and if it is exceeded, we sleep.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/drivers/md/dm-raid1.c b/drivers/md/dm-raid1.c
index e2ea97723e10..d053098c6a91 100644
--- a/drivers/md/dm-raid1.c
+++ b/drivers/md/dm-raid1.c
@@ -82,6 +82,9 @@ struct mirror_set {
         struct mirror mirror[0];
 };
 
+DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(raid1_resync_throttle,
+                "A percentage of time allocated for raid resynchronization");
+
 static void wakeup_mirrord(void *context)
 {
         struct mirror_set *ms = context;
@@ -1111,7 +1114,7 @@ static int mirror_ctr(struct dm_target *ti, unsigned int argc, char **argv)
                 goto err_destroy_wq;
         }
 
-        ms->kcopyd_client = dm_kcopyd_client_create();
+        ms->kcopyd_client = dm_kcopyd_client_create(&dm_kcopyd_throttle);
         if (IS_ERR(ms->kcopyd_client)) {
                 r = PTR_ERR(ms->kcopyd_client);
                 goto err_destroy_wq;