Date: Wed, 10 Mar 2004 12:41:09 -0800 (PST) From: Poul-Henning Kamp <phk@FreeBSD.org> To: src-committers@FreeBSD.org, cvs-src@FreeBSD.org, cvs-all@FreeBSD.org Subject: cvs commit: src/sys/sys mdioctl.h src/sys/dev/md md.c src/sbin/mdconfig mdconfig.8 mdconfig.c Message-ID: <200403102041.i2AKf90l061660@repoman.freebsd.org>
next in thread | raw e-mail | index | archive | help
phk 2004/03/10 12:41:09 PST
FreeBSD src repository
Modified files:
sys/sys mdioctl.h
sys/dev/md md.c
sbin/mdconfig mdconfig.8 mdconfig.c
Log:
Fix a long-standing deadlock issue with vnode backed md(4) devices:
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.
Revision Changes Path
1.27 +3 -0 src/sbin/mdconfig/mdconfig.8
1.31 +5 -1 src/sbin/mdconfig/mdconfig.c
1.115 +5 -3 src/sys/dev/md/md.c
1.14 +1 -0 src/sys/sys/mdioctl.h
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200403102041.i2AKf90l061660>