Date: Mon, 12 Mar 2001 15:23:24 -0800 From: Alfred Perlstein <bright@wintelcom.net> To: "Justin T. Gibbs" <gibbs@scsiguy.com> Cc: Soren Schmidt <sos@freebsd.dk>, Kevin Oberman <oberman@es.net>, scsi@FreeBSD.ORG, fs@FreeBSD.ORG, dillon@FreeBSD.ORG Subject: Re: Disk I/O problem in 4.3-BETA Message-ID: <20010312152324.H18351@fw.wintelcom.net> In-Reply-To: <200103122319.f2CNJ8s42439@aslan.scsiguy.com>; from gibbs@scsiguy.com on Mon, Mar 12, 2001 at 04:19:08PM -0700 References: <20010312151024.E18351@fw.wintelcom.net> <200103122319.f2CNJ8s42439@aslan.scsiguy.com>
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cc'd -fs and Matt. :)
* Justin T. Gibbs <gibbs@scsiguy.com> [010312 15:19] wrote:
> >All i need to know is if there's a way to look at a particular
> >struct bio/buf and determine if there's a need to write the
> >data sync. Soren claims that B_ORDERED is not the magic bit that's
> >needed, is there one? Or are we SOL on the kernel communicating the
> >need for a block to be written "right now" and not complete until
> >sync'd to the backing storage's non-volatile media?
>
> Most, if not all, of the kernel assumes that the data is committed to
> non-volatile storage when the write is notified as complete. FFS
> and softupdates could survive if they marked meta data or the first
> buffer across a dependency domain respectively as B_ORDERED assuming
> the device commits to media in the expected order, but softupdates
> doesn't do this, and FFS probably doesn't do this correctly.
Hmm, it wouldn't be that hard to have the bwrite() functions
something with the buf that says, I'm waiting for this to complete
and it damn better be complete when i get it back.
(*)
The ones that wait for completetion rather than bawrite() which
just asks for an async write.
The only problem with this is that sometimes bwrite is used when
there's a shortage and it'd be nice to be able to take advantage
of write caching in those instances.
Hopefully one of us will look into it one of these days.
--
-Alfred Perlstein - [bright@wintelcom.net|alfred@freebsd.org]
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