From: Blaisorblade <blaisorblade@yahoo.it>
To: user-mode-linux-devel@lists.sourceforge.net
Cc: Chris Lightfoot <chris@ex-parrot.com>, Jeff Dike <jdike@addtoit.com>
Subject: Re: [uml-devel] ubd and write barriers
Date: Tue, 4 Oct 2005 12:31:56 +0200 [thread overview]
Message-ID: <200510041231.56985.blaisorblade@yahoo.it> (raw)
In-Reply-To: <HDubM/jULNDp.FiIUPkbI/sUT/mvVu1/2/A@sphinx.mythic-beasts.com>
On Tuesday 04 October 2005 11:31, Chris Lightfoot wrote:
> The current ubd implementation doesn't support write
> barriers (blk_queue_ordered etc.), and the reccomendation
> is to use synchronous IO to ensure data integrity. In
> principle, adding barrier request support ought to get
> around this problem, allowing writes without O_SYNC with
> occasional calls to fdatasync on the underlying data (the
> motivation for write barrier support was safety of
> journalling filesystems on disks with write caches, an
> analogous problem).
Yes, I more or less remembered that was the idea (from readings on lwn.net),
thanks for confirming it.
> ext3 and reiserfs support the write barrier stuff if
> mounted with appropriate options (barrier=1 and
> barrier=flush respectively).
So they don't auto-enable this when support exists? I.e. everybody is running
slower just because we don't add those params?
> Implementing this ought to give performance somewhere
> between ubdXs and ubdX, but with adequate guarantees of
> data integrity for use with modern filesystems. That said,
> I haven't measured this yet.
> A patch for this is pretty simple (see below). Has there
> been discussion of this before? I couldn't find any in the
> list archives....
This was discussed between me and Jeff recently, even if maybe that was
off-list.
--
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade
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next prev parent reply other threads:[~2005-10-04 10:31 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-10-04 9:31 [uml-devel] ubd and write barriers Chris Lightfoot
2005-10-04 10:31 ` Blaisorblade [this message]
2005-10-04 10:42 ` Chris Lightfoot
2005-10-12 22:11 ` Adam Heath
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