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, 44 insertions, 0 deletions

diff --git a/sys/kern/vfs_cache.c b/sys/kern/vfs_cache.c
index cb4ea94..5fe0382 100644
--- a/sys/kern/vfs_cache.c
+++ b/sys/kern/vfs_cache.c
@@ -327,11 +327,17 @@ sysctl_debug_hashstat_rawnchash(SYSCTL_HANDLER_ARGS)
 	struct namecache *ncp;
 	int i, error, n_nchash, *cntbuf;
 
+retry:
 	n_nchash = nchash + 1;	/* nchash is max index, not count */
 	if (req->oldptr == NULL)
 		return SYSCTL_OUT(req, 0, n_nchash * sizeof(int));
 	cntbuf = malloc(n_nchash * sizeof(int), M_TEMP, M_ZERO | M_WAITOK);
 	CACHE_RLOCK();
+	if (n_nchash != nchash + 1) {
+		CACHE_RUNLOCK();
+		free(cntbuf, M_TEMP);
+		goto retry;
+	}
 	/* Scan hash tables counting entries */
 	for (ncpp = nchashtbl, i = 0; i < n_nchash; ncpp++, i++)
 		LIST_FOREACH(ncp, ncpp, nc_hash)
@@ -930,6 +936,44 @@ nchinit(void *dummy __unused)
 }
 SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_SECOND, nchinit, NULL);
 
+void
+cache_changesize(int newmaxvnodes)
+{
+	struct nchashhead *new_nchashtbl, *old_nchashtbl;
+	u_long new_nchash, old_nchash;
+	struct namecache *ncp;
+	uint32_t hash;
+	int i;
+
+	new_nchashtbl = hashinit(newmaxvnodes * 2, M_VFSCACHE, &new_nchash);
+	/* If same hash table size, nothing to do */
+	if (nchash == new_nchash) {
+		free(new_nchashtbl, M_VFSCACHE);
+		return;
+	}
+	/*
+	 * Move everything from the old hash table to the new table.
+	 * None of the namecache entries in the table can be removed
+	 * because to do so, they have to be removed from the hash table.
+	 */
+	CACHE_WLOCK();
+	old_nchashtbl = nchashtbl;
+	old_nchash = nchash;
+	nchashtbl = new_nchashtbl;
+	nchash = new_nchash;
+	for (i = 0; i <= old_nchash; i++) {
+		while ((ncp = LIST_FIRST(&old_nchashtbl[i])) != NULL) {
+			hash = fnv_32_buf(nc_get_name(ncp), ncp->nc_nlen,
+			    FNV1_32_INIT);
+			hash = fnv_32_buf(&ncp->nc_dvp, sizeof(ncp->nc_dvp),
+			    hash);
+			LIST_REMOVE(ncp, nc_hash);
+			LIST_INSERT_HEAD(NCHHASH(hash), ncp, nc_hash);
+		}
+	}
+	CACHE_WUNLOCK();
+	free(old_nchashtbl, M_VFSCACHE);
+}
 
 /*
  * Invalidate all entries to a particular vnode.