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When deleting files on filesystems that are stored on flash-memory (solid-state) disk drives, the filesystem notifies the underlying disk of the blocks that it is no longer using. The notification allows the drive to avoid saving these blocks when it needs to flash (zero out) one of its flash pages. These notifications of no-longer-being-used blocks are referred to as TRIM notifications. In FreeBSD these TRIM notifications are sent from the filesystem to the drive using the BIO_DELETE command. Until now, the filesystem would send a separate message to the drive for each block of the file that was deleted. Each Gigabyte of file size resulted in over 3000 TRIM messages being sent to the drive. This burst of messages can overwhelm the drive's task queue causing multiple second delays for read and write requests. This implementation collects runs of contiguous blocks in the file and then consolodates them into a single BIO_DELETE command to the drive. The BIO_DELETE command describes the run of blocks as a single large block being deleted. Each Gigabyte of file size can result in as few as two BIO_DELETE commands and is typically less than ten. Though these larger BIO_DELETE commands take longer to run, they do not clog the drive task queue, so read and write commands can intersperse effectively with them. Though this new feature has been throughly reviewed and tested, it is being added disabled by default so as to minimize the possibility of disrupting the upcoming 12.0 release. It can be enabled by running ``sysctl vfs.ffs.dotrimcons=1''. Users are encouraged to test it. If no problems arise, we will consider requesting that it be enabled by default for 12.0. Reviewed by: kib Tested by: Peter Holm Sponsored by: Netflix
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The Makefile in this directory supports a number of targets for building components (or all) of the FreeBSD source tree. See build(7), config(8), https://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/makeworld.html, and https://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/kernelconfig.html for more information, including setting make(1) variables.
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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.
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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.
stand Boot loader sources.
sys Kernel sources.
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used in release builds. NOTES contains documentation of
all possible entries.
tests Regression tests which can be run by Kyua. See tests/README
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usr.bin User commands.
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