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, 16 insertions, 0 deletions

diff --git a/sys/i386/include/param.h b/sys/i386/include/param.h
index dffc648..6241389 100644
--- a/sys/i386/include/param.h
+++ b/sys/i386/include/param.h
@@ -113,6 +113,22 @@
 #define UPAGES	2		/* pages of u-area */
 
 /*
+ * Ceiling on amount of swblock kva space.
+ */
+#ifndef VM_SWZONE_SIZE_MAX
+#define VM_SWZONE_SIZE_MAX	(70 * 1024 * 1024)
+#endif
+
+/*
+ * Ceiling on size of buffer cache (really only effects write queueing,
+ * the VM page cache is not effected).
+ */
+#ifndef VM_BCACHE_SIZE_MAX
+#define VM_BCACHE_SIZE_MAX	(200 * 1024 * 1024)
+#endif
+
+
+/*
  * Constants related to network buffer management.
  * MCLBYTES must be no larger than PAGE_SIZE.
  */