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, 5 insertions, 2 deletions

diff --git a/sys/vm/swap_pager.c b/sys/vm/swap_pager.c
index f2d6061..e25a556 100644
--- a/sys/vm/swap_pager.c
+++ b/sys/vm/swap_pager.c
@@ -323,10 +323,13 @@ swap_pager_swap_init()
 	/*
 	 * Initialize our zone.  Right now I'm just guessing on the number
 	 * we need based on the number of pages in the system.  Each swblock
-	 * can hold 16 pages, so this is probably overkill.
+	 * can hold 16 pages, so this is probably overkill.  This reservation
+	 * is typically limited to around 70MB by default.
 	 */
 
-	n = min(cnt.v_page_count, (kernel_map->max_offset - kernel_map->min_offset) / PAGE_SIZE) * 2;
+	n = cnt.v_page_count;
+	if (maxswzone && n > maxswzone / sizeof(struct swblock))
+		n = maxswzone / sizeof(struct swblock);
 	n2 = n;
 
 	do {