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, 1 deletions

diff --git a/sys/amd64/amd64/machdep.c b/sys/amd64/amd64/machdep.c
index 489e277..7bc1d3d 100644
--- a/sys/amd64/amd64/machdep.c
+++ b/sys/amd64/amd64/machdep.c
@@ -299,7 +299,9 @@ again:
 	 * The nominal buffer size (and minimum KVA allocation) is BKVASIZE.
 	 * For the first 64MB of ram nominally allocate sufficient buffers to
 	 * cover 1/4 of our ram.  Beyond the first 64MB allocate additional
-	 * buffers to cover 1/20 of our ram over 64MB.
+	 * buffers to cover 1/20 of our ram over 64MB.  When auto-sizing
+	 * the buffer cache we limit the eventual kva reservation to
+	 * maxbcache bytes.
 	 *
 	 * factor represents the 1/4 x ram conversion.
 	 */
@@ -312,6 +314,9 @@ again:
 			    16384 / factor);
 		if (physmem_est > 16384)
 			nbuf += (physmem_est - 16384) * 2 / (factor * 5);
+
+		if (maxbcache && nbuf > physmem_est / BKVASIZE)
+			nbuf = maxbcache / BKVASIZE;
 	}
 
 	/*