05877a8595
If filesystem block size is less than the page size, it is possible that the page-out run contains partially clean pages. E.g., the chunk of the page might be bdwrite()-ed, or some thread performed bwrite() on a buffer which references a chunk of the paged out page. As result, the assertion added in r319975, which checked that all pages in the run are dirty, does not hold on such filesystems. One solution is to remove the assert, but it is undesirable, because we do overwrite the valid on-disk content. I cannot provide a scenario where such write would corrupt the file data, but I do not like it on principle. Another, in my opinion proper, solution is to only write parts of the pages still marked dirty. The patch implements this, it skips clean blocks and only writes the dirty block runs. Note that due to clustering, write one page might clean other pages in the run, so the next write range must be calculated only after the current range is written out. More, due to a possible invalidation, and the fact that the object lock is dropped and reacquired before the checks, it is possible that the whole page-out pages run appears to consist of only clean pages. For this reason, it is impossible to assert that there is some work for the pageout method to do (i.e. assert that there is at least one dirty page in the run). But such clearing can only occur due to invalidation, and not due to a parallel write, because we own the vnode lock exclusive. Reported by: fsu In collaboration with: pho Reviewed by: alc, markj Sponsored by: The FreeBSD Foundation MFC after: 3 weeks Differential revision: https://reviews.freebsd.org/D12668
FreeBSD Source:
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. See build(7) and 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. See build(7), config(8), and http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/kernelconfig.html for more information.
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 kernel configuration files reside in the sys/<arch>/conf
sub-directory. GENERIC is the default configuration used in release builds.
NOTES contains entries and documentation for all possible
devices, not just those commonly used.
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.
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.
tests Regression tests which can be run by Kyua. See tests/README
for additional information.
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