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In order to determine what to page out, the vm_daemon checks reference bits on all pages belonging to all processes. Unfortunately, the algorithm used reacted badly with shared pages; each shared page would be checked once per process sharing it; this caused an O(N^2) growth of tlb invalidations. The algorithm has been changed so that each page will be checked only 16 times. Prior to this change, a fork/sleepbomb of 1300 processes could cause the vm_daemon to take over 60 seconds to complete, effectively freezing the system for that time period. With this change in place, the vm_daemon completes in less than a second. Any system with hundreds of processes sharing pages should benefit from this change. Note that the vm_daemon is only run when the system is under extreme memory pressure. It is likely that many people with loaded systems saw no symptoms of this problem until they reached the point where swapping began. Special thanks go to dillon, peter, and Chuck Cranor, who helped me get up to speed with vm internals. PR: 33542, 20393 Reviewed by: dillon MFC after: 1 week
This is the top level of the FreeBSD source directory. This file was last revised on: $FreeBSD$ For copyright information, please see the file COPYRIGHT in this directory (additional copyright information also exists for some sources in this tree - please see the specific source directories for more information). The Makefile in this directory supports a number of targets for building components (or all) of the FreeBSD source tree, the most commonly used one being ``world'', which rebuilds and installs everything in the FreeBSD system from the source tree except the kernel, the kernel-modules and the contents of /etc. The ``buildkernel'' and ``installkernel'' targets build and install the kernel and the modules (see below). Please see the top of the Makefile in this directory for more information on the standard build targets and compile-time flags. Building a kernel is a somewhat more involved process, documentation for which can be found at: http://www.freebsd.org/handbook/kernelconfig.html And in the config(8) man page. Note: If you want to build and install the kernel with the ``buildkernel'' and ``installkernel'' targets, you have to build world before. More information is available in the handbook. The sample kernel configuration files reside in the sys/i386/conf sub-directory (assuming that you've installed the kernel sources), the file named GENERIC being the one used to build your initial installation kernel. The file NOTES contains entries and documentation for all possible devices, not just those commonly used. It is the successor of the ancient LINT file, but in contrast to LINT, it is not buildable as a kernel but a pure reference and documentation file. Source Roadmap: --------------- bin System/User commands. contrib Packages contributed by 3rd parties. crypto Cryptography stuff (see crypto/README). etc Template files for /etc games Amusements. gnu Various commands and libraries under the GNU Public License. Please see gnu/COPYING* for more information. include System include files. kerberosIV Kerberos package. lib System libraries. libexec System daemons. release Release building Makefile & associated tools. sbin System commands. secure Cryptographic libraries and commands. share Shared resources. sys Kernel sources. tools Utilities for regression testing and miscellaneous tasks. usr.bin User commands. usr.sbin System administration commands. For information on synchronizing your source tree with one or more of the FreeBSD Project's development branches, please see: http://www.freebsd.org/handbook/synching.html