linux-kernel - Re: processes in D state too long too often

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Message-ID: <20090210160227.GC29075@fieldses.org>
Date:	Tue, 10 Feb 2009 11:02:27 -0500
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	"Gary L. Grobe" <gary@...be.net>
Cc:	linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: processes in D state too long too often

On Tue, Feb 10, 2009 at 01:04:10AM +0000, Gary L. Grobe wrote:
> >Presumably that's the msleep(10) in nfsd_vfs_write().
> >
> >That wouldn't explain the same nfsd thread waiting for several seconds,
> >though.  Or was it just that that several seconds during which different
> >nfsd threads were stuck in D, not necessarily the same ones?
> >
> >What does your /etc/exports file look like on the server, and what are
> >the mount options on the client?
> >
> >You could try turning off that msleep() with no_wdelay, but it may not
> >help.
> >
> >The more likely explanation is that you just switched to a more recent
> >distro where "sync" (as opposed to "async") is the option.  Depending on
> >workload, "async" may improve performance a great deal, at the expense
> >of possible data corruption on server reboot!
> >
> >If you're doing a lot of writing and using NFSv2, then switching to
> >NFSv3 may give you performance close to the "async" performance without
> >the corruption worries.
> 
> Apologies for the unintentional separate thread.
> 
> I really think I'm seeing the same nfsd threads going into D for a very short time. Here's what's in /etc/exports ...
> 
> /diskless/10.0.1.1 10.0.1.1(sync,rw,no_root_squash,no_all_squash,no_subtree_check)
> /diskless/10.0.1.2 10.0.1.2(sync,rw,no_root_squash,no_all_squash,no_subtree_check)
> /diskless/10.0.1.3 10.0.1.3(sync,rw,no_root_squash,no_all_squash,no_subtree_check)
> # ... same lines above for another 80+ nodes
> 
> # Common to all slave nodes.
> /usr    10.0.0.0/16(sync,ro,subtree_check,no_root_squash,no_all_squash)
> /opt    10.0.0.0/16(sync,rw,no_subtree_check,no_root_squash,no_all_squash)
> /home   10.0.0.0/16(sync,rw,no_subtree_check,no_root_squash,no_all_squash)
> #/var/log 10.0.0.0/16(sync,rw,subtree_check,no_root_squash,no_all_squash)
> 
> Mount options on each client are as follows ...
> 
> 10.0.0.10:/diskless/10.0.1.1    /   nfs     sync,hard,intr,rw,rsize=8192,wsize=8192 0   0
> 10.0.0.10:/opt          /opt    nfs sync,hard,intr,rw,rsize=8192,wsize=8192 0   0
> 10.0.0.10:/usr          /usr    nfs sync,hard,intr,ro,rsize=8192,wsize=8192 0   0
> 10.0.0.10:/home         /home   nfs sync,hard,intr,rw,rsize=8192,wsize=8192 0   0
> none                    /proc   proc    defaults    0 0
> #10.0.0.10:/var/log     /var/log nfs    sync,hard,intr,rw   0 0
> 
> I'm not following turning off the msleep() option. Where are you referring to this from?

If you add no_wdelay to the export options, then we won't see the
mdelay() calls in the sysrq-w output anymore.  I doubt that'll solve the
problem, but it may be worth a try just to see what changes.

> I've got NFSv3 enabled and have used this in a previous installation
> (using the same distro, gentoo) on this same hardware with no issues,
> and 'sync', and the performance was much better.

OK, then I'm out of theories for now....

--b.

> Something worth
> noting, I've rolled back my kernel several times now and each time I
> go back (w/ same vers on master and slave node), the D state time in
> simulation processes keeps getting better (cut down). I went from
> 2.6.27-r7 to 2.6.24-r8 and now I'm running 2.6.20-r10, and each one
> better than the previous (and later) kernel. I was running 2.6.18-r2
> in the past, which I'm having difficulties getting at the moment.
> 
> 
> 
> 
> 
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