vol: rate-limit volume usage updates

Add threshold and time rate-limit parameters for volume usage
updates to disk.  This reduces the amount of i/o needed for
volume usage statistics on very busy fileservers.  Set the
default to limit updates to one every 5 seconds per volume.

Change-Id: I6b4274476ef6b8f9e4288b109d5a3edbdea6e91c
Reviewed-on: http://gerrit.openafs.org/5803
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Reviewed-by: Tom Keiser <tkeiser@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>

diff --git a/src/vol/volume.c b/src/vol/volume.c
index 319aeab..ba8ed51 100644 (file)
--- a/src/vol/volume.c
+++ b/src/vol/volume.c
@@ -479,6 +479,8 @@ VOptDefaults(ProgramType pt, VolumePackageOptions *opts)
     opts->interrupt_rxcall = NULL;
     opts->offline_timeout = -1;
     opts->offline_shutdown_timeout = -1;
+    opts->usage_threshold = 128;
+    opts->usage_rate_limit = 5;
 
 #ifdef FAST_RESTART
     opts->unsafe_attach = 1;
@@ -6674,10 +6676,16 @@ VBumpVolumeUsage_r(Volume * vp)
     if (now - V_dayUseDate(vp) > OneDay)
        VAdjustVolumeStatistics_r(vp);
     /*
-     * Save the volume header image to disk after every 128 bumps to dayUse.
+     * Save the volume header image to disk after a threshold of bumps to dayUse,
+     * at most every usage_rate_limit seconds.
      */
-    if ((V_dayUse(vp)++ & 127) == 0) {
+    V_dayUse(vp)++;
+    vp->usage_bumps_outstanding++;
+    if (vp->usage_bumps_outstanding >= vol_opts.usage_threshold
+       && vp->usage_bumps_next_write <= now) {
        Error error;
+       vp->usage_bumps_outstanding = 0;
+       vp->usage_bumps_next_write = now + vol_opts.usage_rate_limit;
        VUpdateVolume_r(&error, vp, VOL_UPDATE_WAIT);
     }
 }

diff --git a/src/vol/volume.h b/src/vol/volume.h
index 1b9c7b6..4ba4494 100644 (file)
--- a/src/vol/volume.h
+++ b/src/vol/volume.h
@@ -271,6 +271,9 @@ typedef struct VolumePackageOptions {
                                    *   during shutdown, we will still only wait
                                    *   for this amount of time in total, not e.g.
                                    *   for each going-offline volume encountered. */
+    afs_int32 usage_threshold;    /*< number of accesses before writing volume header */
+    afs_int32 usage_rate_limit;   /*< minimum number of seconds before writing volume
+                                   *  header, after usage_threshold is exceeded */
 } VolumePackageOptions;
 
 /* Magic numbers and version stamps for each type of file */
@@ -717,6 +720,8 @@ typedef struct Volume {
     VolumeVLRUState vlru;         /* state specific to the VLRU */
     FSSYNC_VolOp_info * pending_vol_op;  /* fssync command info for any pending vol ops */
 #endif /* AFS_DEMAND_ATTACH_FS */
+    int usage_bumps_outstanding; /**< to rate limit the usage update i/o by accesses */
+    int usage_bumps_next_write;  /**< to rate limit the usage update i/o by time */
 } Volume;
 
 struct volHeader {