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Date: Fri, 13 Dec 2013 20:32:56 +0100
From: Sander Klein <roedie@roedie.nl>
To: "J. Bruce Fields" <bfields@fieldses.org>
Cc: linux-nfs@vger.kernel.org, linux-nfs-owner@vger.kernel.org
Subject: Re: rpc.mountd high cpu usage
In-Reply-To: <20131212212213.GC13467@fieldses.org>
References: <889b64df295ba04d47f941762ebe0bac@roedie.nl>
 <20131212154642.GA11521@fieldses.org>
 <3e92cb841fa81d6a16f3d471cdd8bb20@roedie.nl>
 <20131212212213.GC13467@fieldses.org>
Message-ID: <c50ec8735833f8c05a351928ae48b6df@roedie.nl>
Sender: linux-nfs-owner@vger.kernel.org

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.

Greets,

Sander