Date: Tue, 23 May 2006 15:41:07 -0400 From: Kris Kennaway <kris@obsecurity.org> To: mlfbsd <mlfbsd@cognet.ci0.org> Cc: Giorgos Keramidas <keramida@ceid.upatras.gr>, current@freebsd.org, Kris Kennaway <kris@obsecurity.org> Subject: Re: md /tmp and async mounts Message-ID: <20060523194106.GA46634@xor.obsecurity.org> In-Reply-To: <20060523143013.GA11472@ci0.org> References: <20060522211223.GA3621@xor.obsecurity.org> <20060522231437.GC1446@odin.ac.hmc.edu> <20060523133037.GA2908@gothmog.pc> <20060523143013.GA11472@ci0.org>
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On Tue, May 23, 2006 at 04:30:13PM +0200, mlfbsd wrote:
> On Tue, May 23, 2006 at 04:30:37PM +0300, Giorgos Keramidas wrote:
> > On 2006-05-22 16:14, Brooks Davis <brooks@one-eyed-alien.net> wrote:
> > >On Mon, May 22, 2006 at 05:12:24PM -0400, Kris Kennaway wrote:
> > >> I noticed that with tmpmfs in rc.conf, the md is not being mounted
> > >> with -o async; this is an enormous performance boost, so is there a
> > >> reason it is not used, or just that it was overlooked?
> > >
> > > Just overlooked as far as I know. We correctly switched to not mount=
ing
> > > with softupdates, but should probably switch to -o async.
> >=20
> > Right. The only reasons why the current tmpmfs_flags doesn't
> > include the `-o async' option too are:
> >=20
> > a) It didn't back when it was all hardcoded in the script
> >=20
> > b) I didn't think about adding it by default when revision
> > 1.230 of src/etc/defaults/rc.conf was committed by me
> >=20
> > If it does improve things, we should probably make the change :)
> >=20
>=20
> The sys/dev/md/md.c rev 1.115 commit log says async used to be the defaul=
t,=20
> but was switched off because it was causing deadlocks. Did this get fixed
> since ?
You are confusing mdconfig's -o async mode, used only for vnode
backing (not the case here anyway):
[no]async
For vnode backed devices: avoid IO_SYNC for increased
performance but at the risk of deadlocking the entire
kernel.
with mount's -o async mode, used at the filesystem layer on any
device. The latter does not have deadlocks.
Kris
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