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every 30 seconds. This spike in I/O caused the system to pause every 30 seconds which was quite annoying. So, the way that sync worked was changed so that when a vnode was first dirtied, it was put on a 30-second cleaning queue (see the syncer_workitem_pending queues in kern/vfs_subr.c). If the file has not been written or deleted after 30 seconds, the syncer pushes it out. As the syncer runs once per second, dirty files are trickled out slowly over the 30-second period instead of all at once by a call to sync(2). The one drawback to this is that it does not cover the filesystem metadata. To handle the metadata, vfs_allocate_syncvnode() is called to create a "filesystem syncer vnode" at mount time which cycles around the cleaning queue being sync'ed every 30 seconds. In the original design, the only things it would sync for UFS were the filesystem metadata: inode blocks, cylinder group bitmaps, and the superblock (e.g., by VOP_FSYNC'ing devvp, the device vnode from which the filesystem is mounted). Somewhere in its path to integration with FreeBSD the flushing of the filesystem syncer vnode got changed to sync every vnode associated with the filesystem. The result of this change is to return to the old filesystem-wide flush every 30-seconds behavior and makes the whole 30-second delay per vnode useless. This change goes back to the originally intended trickle out sync behavior. Key to ensuring that all the intended semantics are preserved (e.g., that all inode updates get flushed within a bounded period of time) is that all inode modifications get pushed to their corresponding inode blocks so that the metadata flush by the filesystem syncer vnode gets them to the disk in a timely way. Thanks to Konstantin Belousov (kib@) for doing the audit and commit -r231122 which ensures that all of these updates are being made. Reviewed by: kib Tested by: scottl MFC after: 2 weeks
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 ``world'' target should only be used in cases where the source tree has not changed from the currently running version. See: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/makeworld.html for more information, including setting make(1) variables. 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/doc/en_US.ISO8859-1/books/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 might need to build world before. More information is available in the handbook. The sample kernel configuration files reside in the sys/<arch>/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. cddl Various commands and libraries under the Common Development and Distribution License. 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. kerberos5 Kerberos5 (Heimdal) package. lib System libraries. libexec System daemons. release Release building Makefile & associated tools. rescue Build system for statically linked /rescue utilities. 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/doc/en_US.ISO8859-1/books/handbook/synching.html