implement not double-caching for reads from vnode-backed md devices.
Use VOP_ADVISE() similarly instead of !IO_DIRECT unsimilarly for writes.
Add a "cache" option to mdconfig to allow changing the default of not
caching.
This depends on a recent commit to fix VOP_ADVISE(). A previous version
had optimizations for sequential i/o's (merge the i/o's and only uncache
for discontiguous i/o's and for full blocks), but optimizations and
knowledge of block boundaries belong in VOP_ADVISE(). Read-ahead should
also be handled better, by supporting it in md and discarding it in
VOP_ADVISE().
POSIX_FADV_DONTNEED is ignored by zfs, but so is IO_DIRECT.
POSIX_FADV_DONTNEED works better than IO_DIRECT if it is not ignored,
since it only discards from the buffer cache immediately, while
IO_DIRECT also discards from the page cache immediately.
IO_DIRECT was not used for writes since it was claimed to be too slow,
but most of the slowness for writes is from doing them synchronously by
default. Non-synchronous writes still deadlock in many cases.
IO_DIRECT only has a special implementation for ffs reads with DIRECTIO
configured. Otherwise, if it is not ignored than it uses the buffer and
page caches normally except for discarding everything after each i/o,
and then it has much the same overheads as POSIX_FADV_DONTNEED. The
overheads for reading with ffs and DIRECTIO were similar in tests of md.
Reviewed by: kib
This feature comes from the fact that we rely memory-backed md(4)
in our build process heavily. However, if the build goes haywire
the allocated resources (i.e. swap and memory-backed md(4)'s) need
to be purged. It is extremely useful to have ability to attach
arbitrary labels to each of the virtual disks so that they can
be identified and GC'ed if neecessary.
MFC after: 4 weeks
Differential Revision: https://reviews.freebsd.org/D10457
Add -o [no]verify option to mdconfig (and document in man page.)
Implement GEOM attribute MNT::verified to ask md if the backing vnode is
verified.
Check for MNT::verified in cd9660 mount to flag the mount as MNT_VERIFIED if
the underlying device has been verified.
Reviewed by: rwatson
Approved by: sjg (mentor)
Obtained from: Juniper Networks, Inc.
Differential Revision: https://reviews.freebsd.org/D2902
go asking what debug flags to set for GEOM to make it work. Advice
them to use gpart(8) instead.
Something similar should probably done with disklabel,
but I need to rewrite the disklabel examples first.
Reviewed by: wblock@
MFC after: 1 month
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D3315
section. This removes stuff that doesn't really belong there,
and simplifies examples for the basic operations.
Reviewed by: wblock@
MFC after: 1 month
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D3198
when -u is specified it is not...
update the docs to say that you can use full device names w/ -u, and
update the examples...
Submitted by: #vbsdcon
MFC after: 3 days
specified, only md(4) devices which have the specified file as backing
store are displayed.
- Use MD_NAME instead of "md".
- Use _PATH_DEV instead of "/dev/".
MFC after: 1 week
"mdconfig -f file", I decided that it would be easier to make mdconfig
DWIM than to teach my fingers to type the correct command line.
MFC after: 3 weeks
After this change it should be possible to use very big md(4) devices.
- Clean up and simplify the code a bit.
- Use humanize_number(3) to print size of md(4) devices.
- Add 't' suffix which stands for terabyte.
- Make '-S' to really work with all types of devices.
- Other minor changes.
On vnode backed md(4) devices over a certain, currently undetermined
size relative to the buffer cache our "lemming-syncer" can provoke
a buffer starvation which puts the md thread to sleep on wdrain.
This generally tends to grind the entire system to a stop because the
event that is supposed to wake up the thread will not happen until a fair
bit of the piled up I/O requests in the system finish, and since a lot
of those are on a md(4) vnode backed device which is currently waiting
on wdrain until a fair amount of the piled up ... you get the picture.
The cure is to issue all VOP_WRITES on the vnode backing the device
with IO_SYNC.
In addition to more closely emulating a real disk device with a
non-lying write-cache, this makes the writes exempt from rate-limited
(there to avoid starving the buffer cache) and consequently prevents
the deadlock.
Unfortunately performance takes a hit.
Add "async" option to give people who know what they are doing the
old behaviour.
number X, rather than mdX, making it easier to script tests that
use md devices but don't want to make assumptions about any existing
md use (such as in diskless environments).
