freebsd kernel with SKQ
a8b0f1009d
that performs the equivalent of an automatic madvise(..., MADV_DONTNEED). The current heuristic, even with the improvements that I made a few years ago, is a good example of making the wrong trade-off, or optimizing for the infrequent case. The infrequent case being reading a single file that is much larger than memory using mmap(2). And, in this case, the page daemon isn't the bottleneck; it's the I/O. In all other cases, the current heuristic has too many false positives, i.e., it caches too many pages that are later reused. To give one example, thousands of pages are cached by the current heuristic during a buildworld and all of them are reactivated before the buildworld completes. In particular, clang reads source files using mmap(2) and there are some relatively large source files in our source tree, e.g., sqlite, that are read multiple times. With the new heuristic, I see fewer false positives and they have a much lower cost. I actually tried something like this more than two years ago and it didn't perform as well as the cache behind heuristic. However, that was before the changes to the page daemon in late summer of 2013 and the existence of pmap_advise(). In particular, with the page daemon doing its work more frequently and in smaller batches, it now completes its work while the application accessing the file is blocked on I/O. Whereas previously, the page daemon appeared to hog the CPU for so long that it caused "hiccups" in the application's execution. Finally, I'll add that the elimination of cache pages is a prerequisite for NUMA support. Reviewed by: jeff, kib Sponsored by: EMC / Isilon Storage Division |
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| bin | ||
| cddl | ||
| contrib | ||
| crypto | ||
| etc | ||
| games | ||
| gnu | ||
| include | ||
| kerberos5 | ||
| lib | ||
| libexec | ||
| release | ||
| rescue | ||
| sbin | ||
| secure | ||
| share | ||
| sys | ||
| tests | ||
| tools | ||
| usr.bin | ||
| usr.sbin | ||
| .arcconfig | ||
| .arclint | ||
| COPYRIGHT | ||
| LOCKS | ||
| MAINTAINERS | ||
| Makefile | ||
| Makefile.inc1 | ||
| ObsoleteFiles.inc | ||
| README | ||
| UPDATING | ||
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