From: Simon Peter <simon.peter@gmx.de>
Subject: Re: Delays on "first" access to a NFS mount
Date: Wed, 7 Mar 2007 19:44:18 +0100
Message-ID: <20070307194418.97fee0ec.simon.peter@gmx.de>
References: <20070307112347.6a40faff.simon.peter@gmx.de>
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Cc: nfs@lists.sourceforge.net,
	"Talpey, Thomas" <Thomas.Talpey@netapp.com>
To: "J. Bruce Fields" <bfields@fieldses.org>
In-Reply-To: <20070307154240.GB26553@fieldses.org>
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> > just verified that the server indeed spins up all disks before
> > answering the request. I thus suspect it is somehow checking all
> > exports whenever any one export is accessed. Is this correct
> > behaviour?
> Hm.  If you have the nfs-utils source, you can see there's a loop in
> 	nfs-utils/utils/mountd/cache.c:nfsd_fh()
> that stats the root of each export, in two places; the first it looks
> like you shouldn't hit if you don't have the mountpoint export option
> set:

Correct. This one is never hit in my case.

> The second is to figure out which filesystem the filehandle that you
> passed in that getattr is for:
>          if (stat(exp->m_export.e_path, &stb) != 0)
>                  continue;

This is where the wait for the respective disk to spin up occurs.

> Could we cache the stat information in the export and then
> double-check it if necessary when there's a match?  Or is there some
> way we could get the kernel to keep that cached for us?

I could certainly cook up a patch for mountd to cache that information
on its own. I don't have too much clue about how the kernel does its
cacheing, though. If it's useful to do that directly in mountd, I could
get my hands on it.

> It seems reasonable to want to export filesystems from a bunch of
> disks without necessarily keeping them all spun up all the time.

This is at least what I would like to see...

Thanks,
Simon

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