On , J. Bruce Fields wrote:
On Fri, Dec 13, 2013 at 08:32:56PM +0100, Sander Klein wrote:
On , J. Bruce Fields wrote:
>>>I think what happens is that exportfs flushes the kernel's export cache
>>>at which point every use of an uncached export triggers an upcall to
>>>mountd. That upcall is probably visible in the strace as a read of a
>>>file descriptor associated with /proc/net/sunrpc/nfsd.fh/content.
>>>
>>>That upcall is handled by nfs-utils/utils/mountd/cache.c:nfsd_fh(),
>>>which is given a filehandle fragment identifying the filesystem in
>>>question and has to match it to an export.
>>>
>>>That's done by match_fsid(). Which does do a stat of the export path,
>>>but not of all the devices.... That's probably happening in one of the
>>>libblkid calls in uuid_by_path()? I wonder if there's something wrong
>>>with libblkid configuration or with the way we're using it?
>>
>>Is there any way I can help getting this fixed? My coding skills are
>>limited but I am very willing to help in any way I can.
>
>I wonder if ltrace could help determine if libblkid is where most of
>those stat's are coming from (and if so, which calls)?
>
>May also be worth reading up on libblkid (man libblkid, etc.) and
>checking your configuration to make sure there's nothing obvious broken
>there. (If so, maybe the libblkid commandline tools would exhibit the
>same problem?)
I didn't have any config in /etc/blkid.conf and the manpage says it
will use EVALUATE=udev,scan which in fact scans through all the
/dev/disk/by-* dirs and parses the /proc/partitions. I put
'EVALUATE=scan' in /etc/blkid.conf but that doesn't help. I
restarted anything NFS related...
I also attached ltrace to the rpc.mountd process. The output of the
trace is at http://pastebin.com/ika1Vetq . I'm not sure what I'm
looking for. The ltrace is done on a server with only 10 harddisks
but the strace showed the same behavour of newfstatat-ing every disk
in a lot of ways.
Hm. I *think* that those SYS_262's are the newfstatat's. And it looks
like they happen as part of the implementation of
blkid_devno_to_devname
(just because you see that call start above the SYS_262's and return
only after).
That is indeed called from utils/mountd/cache.c:get_uuid_blkdev().
So libblkid is mapping device numbers to paths by stat'ing lots of
stuff
under /dev.
I'm not sure what to do about that.... Cc'ing util-linux in case they
can help.
--b.
Anything else I can do to help a bit getting this fixed?
Regards,
Sander
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