Track changes to kern.maxvnodes and appropriately increase or decrease

the size of the name cache hash table (mapping file names to vnodes)
and the vnode hash table (mapping mount point and inode number to vnode).
An appropriate locking strategy is the key to changing hash table sizes
while they are in active use.

Reviewed by: kib
Tested by:   Peter Holm
Differential Revision: https://reviews.freebsd.org/D2265
MFC after:   2 weeks

1 files changed, 19 insertions, 2 deletions

diff --git a/sys/kern/vfs_subr.c b/sys/kern/vfs_subr.c
index 2bc0bc5..410d198 100644
--- a/sys/kern/vfs_subr.c
+++ b/sys/kern/vfs_subr.c
@@ -281,8 +281,25 @@ static enum { SYNCER_RUNNING, SYNCER_SHUTTING_DOWN, SYNCER_FINAL_DELAY }
  * XXX desiredvnodes is historical cruft and should not exist.
  */
 int desiredvnodes;
-SYSCTL_INT(_kern, KERN_MAXVNODES, maxvnodes, CTLFLAG_RW,
-    &desiredvnodes, 0, "Maximum number of vnodes");
+
+static int
+sysctl_update_desiredvnodes(SYSCTL_HANDLER_ARGS)
+{
+	int error, old_desiredvnodes;
+
+	old_desiredvnodes = desiredvnodes;
+	if ((error = sysctl_handle_int(oidp, arg1, arg2, req)) != 0)
+		return (error);
+	if (old_desiredvnodes != desiredvnodes) {
+		vfs_hash_changesize(desiredvnodes);
+		cache_changesize(desiredvnodes);
+	}
+	return (0);
+}
+
+SYSCTL_PROC(_kern, KERN_MAXVNODES, maxvnodes,
+    CTLTYPE_INT | CTLFLAG_MPSAFE | CTLFLAG_RW, &desiredvnodes, 0,
+    sysctl_update_desiredvnodes, "I", "Maximum number of vnodes");
 SYSCTL_ULONG(_kern, OID_AUTO, minvnodes, CTLFLAG_RW,
     &wantfreevnodes, 0, "Minimum number of vnodes (legacy)");
 static int vnlru_nowhere;