FreeBSD src
3c42b5bf28
implementation. The kernel RPC code, which is responsible for the low-level scheduling of incoming NFS requests, contains a throttling mechanism that prevents too much kernel memory from being tied up by NFS requests that are being serviced. When the throttle is engaged, the RPC layer stops servicing incoming NFS sockets, resulting ultimately in backpressure on the clients (if they're using TCP). However, this is a very heavy-handed mechanism as it prevents all clients from making any requests, regardless of how heavy or light they are. (Thus, when engaged, the throttle often prevents clients from even mounting the filesystem.) The throttle mechanism applies specifically to requests that have been received by the RPC layer (from a TCP or UDP socket) and are queued waiting to be serviced by one of the nfsd threads; it does not limit the amount of backlog in the socket buffers. The original implementation limited the total bytes of queued requests to the minimum of a quarter of (nmbclusters * MCLBYTES) and 45 MiB. The former limit seems reasonable, since requests queued in the socket buffers and replies being constructed to the requests in progress will all require some amount of network memory, but the 45 MiB limit is plainly ridiculous for modern memory sizes: when running 256 service threads on a busy server, 45 MiB would result in just a single maximum-sized NFS3PROC_WRITE queued per thread before throttling. Removing this limit exposed integer-overflow bugs in the original computation, and related bugs in the routines that actually account for the amount of traffic enqueued for service threads. The old implementation also attempted to reduce accounting overhead by batching updates until each queue is fully drained, but this is prone to livelock, resulting in repeated accumulate-throttle-drain cycles on a busy server. Various data types are changed to long or unsigned long; explicit 64-bit types are not used due to the unavailability of 64-bit atomics on many 32-bit platforms, but those platforms also cannot support nmbclusters large enough to cause overflow. This code (in a 10.1 kernel) is presently running on production NFS servers at CSAIL. Summary of this revision: * Removes 45 MiB limit on requests queued for nfsd service threads * Fixes integer-overflow and signedness bugs * Avoids unnecessary throttling by not deferring accounting for completed requests Differential Revision: https://reviews.freebsd.org/D2165 Reviewed by: rmacklem, mav MFC after: 30 days Relnotes: yes Sponsored by: MIT Computer Science & Artificial Intelligence Laboratory |
||
|---|---|---|
| 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