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bad324ca54
It is possible for multiple process to sleep concurrently waiting for a buffer. When the buffer shortage is a shortage of space but not a shortage of buffer headers, the processes took turns creating empty buffers and waking each other to advertise the brelse() of the empties; progress was never made because tsleep() always found another high-priority process to run and everything was done at splbio(), so vfs_update never had a chance to flush delayed writes, not to mention that i/o never had a chance to complete. The problem seems to be rare in practice, but it can easily be reproduced by misusing block devices, at least for sufficently slow devices on machines with a sufficiently small buffer cache. E.g., `tar cvf /dev/fd0 /kernel' on an 8MB system with no disk in fd0 causes the problem quickly; the same command with a disk in fd0 causes the problem not quite as quickly; and people have reported problems newfs'ing file systems on block devices. Block devices only cause this problem indirectly. They are pessimized for time and space, and the space pessimization causes the shortage (it manifests as internal fragmentation in buffer_map). This should be fixed in 2.2. |
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| crypto | ||
| eBones | ||
| etc | ||
| games | ||
| gnu | ||
| include | ||
| lib | ||
| libexec | ||
| lkm | ||
| release | ||
| sbin | ||
| secure | ||
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| sys | ||
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| usr.bin | ||
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| COPYRIGHT | ||
| Makefile | ||
| README | ||
This is the top level of the FreeBSD source directory. This file was last revised on: $Id$ 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. Please see the top of the Makefile for more information on the standard build targets and compile-time flags. Building a kernel with config(8) 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. 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 LINT contains entries for all possible devices, not just those commonly used, and is meant more as a general reference than an actual kernel configuration file (a kernel built from it wouldn't even run). Source Roadmap: --------------- bin System/User commands. contrib Packages contributed by 3rd parties. eBones Kerberos package - NOT FOR EXPORT! 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. lib System libraries. libexec System daemons. lkm Loadable Kernel Modules. release Release building Makefile & associated tools. sbin System commands. secure DES and DES-related utilities - NOT FOR EXPORT! 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