From: mjg <mjg@FreeBSD.org>
Date: Tue, 10 Sep 2019 20:11:00 +0000 (+0000)
Subject: cache: change the formula for calculating lock array sizes
X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=5924940444ff6e760b180757440a41c85c380244;p=freebsd.git

cache: change the formula for calculating lock array sizes

It used to be mp_ncpus * 64, but this gives unnecessarily big values for small
machines and at the same time constraints bigger ones. In particular this helps
on a 104-way box for which the count is now doubled.

While here make cache_purgevfs less likely. Currently it is not efficient in
face of contention due to lock ordering issues. These are fixable but not worth
it at the moment.

Sponsored by:	The FreeBSD Foundation
---

diff --git a/sys/kern/vfs_cache.c b/sys/kern/vfs_cache.c
index 61d51c98f39..d45bc43052c 100644
--- a/sys/kern/vfs_cache.c
+++ b/sys/kern/vfs_cache.c
@@ -1879,19 +1879,21 @@ nchinit(void *dummy __unused)
 	    UMA_ZONE_ZINIT);
 
 	nchashtbl = hashinit(desiredvnodes * 2, M_VFSCACHE, &nchash);
-	ncbuckethash = cache_roundup_2(mp_ncpus * 64) - 1;
+	ncbuckethash = cache_roundup_2(mp_ncpus * mp_ncpus) - 1;
+	if (ncbuckethash < 7) /* arbitrarily chosen to avoid having one lock */
+		ncbuckethash = 7;
 	if (ncbuckethash > nchash)
 		ncbuckethash = nchash;
 	bucketlocks = malloc(sizeof(*bucketlocks) * numbucketlocks, M_VFSCACHE,
 	    M_WAITOK | M_ZERO);
 	for (i = 0; i < numbucketlocks; i++)
 		rw_init_flags(&bucketlocks[i], "ncbuc", RW_DUPOK | RW_RECURSE);
-	ncvnodehash = cache_roundup_2(mp_ncpus * 64) - 1;
+	ncvnodehash = ncbuckethash;
 	vnodelocks = malloc(sizeof(*vnodelocks) * numvnodelocks, M_VFSCACHE,
 	    M_WAITOK | M_ZERO);
 	for (i = 0; i < numvnodelocks; i++)
 		mtx_init(&vnodelocks[i], "ncvn", NULL, MTX_DUPOK | MTX_RECURSE);
-	ncpurgeminvnodes = numbucketlocks;
+	ncpurgeminvnodes = numbucketlocks * 2;
 
 	ncneghash = 3;
 	neglists = malloc(sizeof(*neglists) * numneglists, M_VFSCACHE,