Date: Thu, 11 Mar 2004 10:47:22 +0600 From: Alexey Dokuchaev <danfe@nsu.ru> To: Poul-Henning Kamp <phk@freebsd.org> Cc: cvs-all@freebsd.org Subject: Re: cvs commit: src/sys/sys mdioctl.h src/sys/dev/md md.c src/sbin/mdconfig mdconfig.8 mdconfig.c Message-ID: <20040311044722.GA93643@regency.nsu.ru> In-Reply-To: <200403102041.i2AKf90l061660@repoman.freebsd.org> References: <200403102041.i2AKf90l061660@repoman.freebsd.org>
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On Wed, Mar 10, 2004 at 12:41:09PM -0800, Poul-Henning Kamp wrote: > 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. Just out of curiosity, is your fix a real fix, or just a clever workaround? Meaning, there are some very in-depth issues involved that prevent this problem from being fixed without performance penalty? Thanks. ./danfe
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