describe when zfs_readdir_dnode_prefetch_limit should be used

Signed-off-by: Charles Hedrick <[email protected]>
openzfs · Nov 29, 2024 · e26a454 · e26a454
1 parent 5d8bda9
commit e26a454
Showing 1 changed file with 5 additions and 2 deletions.
diff --git a/man/man4/zfs.4 b/man/man4/zfs.4
@@ -1781,8 +1781,11 @@ all objects in the directory it checks, even if it's just
 looking for a single object.
 Setting this to a non-zero value disables that prefetching for directories
 with a greater size than that value.
-Disabling it for large directories can greatly lower CPU usage on NFS servers
-where directories have a very large number of subdirectories.
+Disabling prefetch for large directories can greatly lower CPU usage on NFS servers
+where directories have a very large number of subdirectories. 
+Consider setting this parameter if your primary access is via NFS, you have
+unusually high CPU used by nfsd processes, and arcstat shows very high metadata
+read rates compared with other activity.
 Directory size in this case is the size returned from calling
 .Sy stat
 on the directory (stat.st_size).