Limit the amount of KVM reserved for the buffer cache and for swap-meta

information.  The default limits only effect machines with > 1GB of ram
and can be overriden with two new kernel conf variables VM_SWZONE_SIZE_MAX
and VM_BCACHE_SIZE_MAX, or with loader variables kern.maxswzone and
kern.maxbcache.  This has the effect of leaving more KVM available for
sizing NMBCLUSTERS and 'maxusers' and should avoid tripups where a sysad
adds memory to a machine and then sees the kernel panic on boot due to
running out of KVM.

Also change the default swap-meta auto-sizing calculation to allocate half
of what it was previously allocating.  The prior defaults were way too high.
Note that we cannot afford to run out of swap-meta structures so we still
stay somewhat conservative here.

1 files changed, 6 insertions, 0 deletions

diff --git a/sys/kern/subr_param.c b/sys/kern/subr_param.c
index 272ca3c..4f755ba 100644
--- a/sys/kern/subr_param.c
+++ b/sys/kern/subr_param.c
@@ -72,6 +72,8 @@ int	maxfilesperproc;		/* per-proc open files limit */
 int	ncallout;			/* maximum # of timer events */
 int	nbuf;
 int	nswbuf;
+int	maxswzone;			/* max swmeta KVA storage */
+int	maxbcache;			/* max buffer cache KVA storage */
 
 /*
  * These have to be allocated somewhere; allocating
@@ -114,6 +116,10 @@ init_param(void)
 	/* Cannot be changed after boot */
 	nbuf = NBUF;
 	TUNABLE_INT_FETCH("kern.nbuf", &nbuf);
+	maxswzone = VM_SWZONE_SIZE_MAX;
+	TUNABLE_INT_FETCH("kern.maxswzone", &maxswzone);
+	maxbcache = VM_BCACHE_SIZE_MAX;
+	TUNABLE_INT_FETCH("kern.maxbcache", &maxbcache);
 	ncallout = 16 + maxproc + maxfiles;
 	TUNABLE_INT_FETCH("kern.ncallout", &ncallout);
 }