Re: Delays on "first" access to a NFS mount

["J. Bruce Fields" <bfields@fieldses.org>]

On Wed, Mar 07, 2007 at 04:06:33PM +0100, Simon Peter wrote:
> 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 mounted. 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:

	 if (exp->m_export.e_mountpoint &&
	     !is_mountpoint(exp->m_export.e_mountpoint[0]?
	                    exp->m_export.e_mountpoint:
	                    exp->m_export.e_path))
		dev_missing ++;

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;
         if (fsidtype == 1 &&
             ((exp->m_export.e_flags & NFSEXP_FSID) == 0 ||
              exp->m_export.e_fsid != fsidnum))
                 continue;
         if (fsidtype != 1) {
                 if (stb.st_ino != inode)
                         continue;
                 if (major != major(stb.st_dev) ||
                     minor != minor(stb.st_dev))
                         continue;
         }
	/* It's a match !! */

You could stick a printf() in there somewhere or something to check whether
this is really where it's waiting.

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?

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

--b.

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