Usermode portion of the support for swap allocation accounting:

- update for getrlimit(2) manpage;
- support for setting RLIMIT_SWAP in login class;
- addition to the limits(1) and sh and csh limit-setting builtins;
- tuning(7) documentation on the sysctls controlling overcommit.

In collaboration with:	pho
Reviewed by:	alc
Approved by:	re (kensmith)

1 files changed, 29 insertions, 0 deletions

diff --git a/share/man/man7/tuning.7 b/share/man/man7/tuning.7
index 9041181..34c8ac3 100644
--- a/share/man/man7/tuning.7
+++ b/share/man/man7/tuning.7
@@ -404,6 +404,35 @@ In this document we will only cover the ones that have the greatest effect
 on the system.
 .Pp
 The
+.Va vm.overcommit
+sysctl defines the overcommit behaviour of the vm subsystem.
+The virtual memory system always does accounting of the swap space
+reservation, both total for system and per-user. Corresponding values
+are available through sysctl
+.Va vm.swap_total,
+that gives the total bytes available for swapping, and
+.Va vm.swap_reserved,
+that gives number of bytes that may be needed to back all currently
+allocated anonymous memory.
+.Pp
+Setting bit 0 of the
+.Va vm.overcommit
+sysctl causes the virtual memory system to return failure
+to the process when allocation of memory causes vm.swap_reserved
+to exceed vm.swap_total.
+Bit 1 of the sysctl enforces RLIMIT_SWAP limit
+(see
+.Xr getrlimit 2 ).
+Root is exempt from this limit.
+Bit 2 allows to count most of the physical
+memory as allocatable, except wired and free reserved pages
+(accounted by
+.Va vm.stats.vm.v_free_target
+and
+.Va vm.stats.vm.v_wire_count
+sysctls, respectively).
+.Pp
+The
 .Va kern.ipc.maxpipekva
 loader tunable is used to set a hard limit on the
 amount of kernel address space allocated to mapping of pipe buffers.