linux-kernel - Re: FS-Cache: Duplicate cookie detected

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Date:   Fri, 8 Mar 2019 09:57:13 -0800 (PST)
From:   Christian Kujau <lists@...dbynature.de>
To:     David Howells <dhowells@...hat.com>
cc:     linux-kernel@...r.kernel.org,
        Anna Schumaker <anna.schumaker@...app.com>,
        Steve Dickson <steved@...hat.com>
Subject: Re: FS-Cache: Duplicate cookie detected

On Fri, 8 Mar 2019, David Howells wrote:
> > $ mount | grep nfs4
> > nfs:/usr/local/src on /usr/local/src type nfs4 (ro,relatime,vers=4.2,rsize=1048576,wsize=1048576,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=192.168.56.139,local_lock=none,addr=192.168.0.115)
> > 
> > ...so FS-Cache ("fsc") isn't even used here.
> 
> Interesting.  Can you do:
> 
> 	cat /proc/fs/nfsfs/volumes

That seems to confirm the mount options, fsc is disabled:

# cat /proc/fs/nfsfs/volumes
NV SERVER   PORT DEV          FSID                              FSC
v4 c0a80073  801 0:46         1cfd45bf1921474d:a795870ea80f5ff7 no

> See the attached for a patch that helps with certain kinds of collision,
> though I can't see that it should help with what you're seeing since the
> RELINQUISHED flag isn't set on the old cookie (fl=222, but 0x10 isn't in
> there).  You can monitor the number of waits by looking in
> /proc/fs/fscache/stats for the:
> 
> 	Acquire: n=289166 nul=0 noc=0 ok=286331 nbf=2 oom=0 wrq=23748

Ah, the wrq= field gets only introduced by this patch. OK, I'll see if I 
can build a test kernel with that and will report back.

Thanks for looking in to this,
Christian.
-- 
BOFH excuse #290:

The CPU has shifted, and become decentralized.