[Linux-cachefs] background mount failing because of FS-Cache?

[Daniel Goering]

Thank you for the detailed answer!

At this point I'm certain that my problem comes from nfs utils,
i.e. mount.nfs, directly and is not related to FS-Cache.

I mailed a detailed description of the issue to
linux-nfs at vger.kernel.org and it seems that the problem is [partially]
solved in more recent kernels.

Cheers
	Daniel


David Howells wrote:
> Daniel Goering <g_daniel at gmx.net> wrote:
> 
>> I'd like to mount an NFS4 share with the option bg as described in man 5
>> nfs.
>> This works perfectly fine e.g. on a Gentoo system. I tried the same with
>> some Fedora 12 clients and the bg option just seems to be ignored. All
>> mounts are carried out in the foreground and time out after 2 minutes
>> [and the client is blocked e.g. during boot for the entire time] instead
>> of trying in the background for about 1 week until the server is back up.
> 
> Have you logged this with bugzilla?
> 
>> The only difference I could find was that Fedora 12 automatically tries
>> to use FS-Cache when issuing the mount and may be FS-Cache forces the
>> whole task into the foreground...
> 
> It does not.
> 
> Apart from setting up a couple of memory structures, no cache-related activity
> is done during mount.  Nothing more happens until the first regular file is
> opened for reading.  Certainly nothing will happen unless you specify an 'fsc'
> option on the mount command line.  You can check this:
> 
> 	[root at andromeda ~]# cat /proc/fs/nfsfs/volumes 
> 	NV SERVER   PORT DEV     FSID              FSC
> 	v4 5a9b4a12  801 0:18    7edcf8bbc93b4329  yes
> 
> As you can see, my test machine has a cached mount - the FSC column says 'yes'.
> 
>> When I issue the mount command I find the following lines in dmesg:
>> FS-Cache: Loaded
>> FS-Cache: Netfs 'nfs' registered for caching
> 
> That just means that the NFS module was loaded and registered itself with
> FS-Cache, which doesn't really mean anything.
> 
>> I certainly did not specify the mount option fsc or anything else to
>> activate FS-Cache and I could not find any option to avoid it.
>> Can someone tell me how to deactivate FS-Cache?
> 
> It isn't necessarily active.  If you want to get rid of FS-Cache completely
> for NFS, you'll have to build a kernel with:
> 
> 	CONFIG_NFS_FSCACHE=y
> 
> changed to 'n'.
> 
>> I tried to blacklist the fscache module, but it was used any ways when
>> issuing mount. Removing the .ko file resulted in a broken nfs module
> 
> nfs.ko depends on fscache.ko.  It wouldn't be able to use it otherwise.
> 
>> Is there a nice way to get rid of FS-Cache or do I have to build my own
>> kernel?
> 
> You'll have to build your own kernel.  I doubt FS-Cache is the problem.
> Unless you activate it by requesting it in a mount option, it won't do
> anything.
> 
> You can also check /proc/fs/fscache/stats.
> 
> You can also turn on NFS debugging for FS-Cache to see what it's doing:
> 
> 	echo $((0x800)) >/proc/sys/sunrpc/nfs_debug 
> 
> David
> 
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