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Date:   Fri, 8 Mar 2019 15:15:14 -0800 (PST)
From:   Christian Kujau <lists@nerdbynature.de>
To:     David Howells <dhowells@redhat.com>
cc:     linux-kernel@vger.kernel.org,
        Anna Schumaker <anna.schumaker@netapp.com>,
        Steve Dickson <steved@redhat.com>
Subject: Re: FS-Cache: Duplicate cookie detected
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On Fri, 8 Mar 2019, David Howells wrote:
> 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

Running Linux v5.0 with this patch applied does indeed still produce the 
"Duplicate cookie detected" messages, but I only ever see wrq=0 when 
running nfstest_cache: 

   https://paste.fedoraproject.org/paste/dkav0FQzYZxE9-V7GphjAQ

(Scroll down until the messages start to appear again)

Only the n= field seems to change during that test:


fedora0# grep wrq n2.log  | sort | uniq -c | sort -n
     28 Acquire: n=8 nul=0 noc=0 ok=1 nbf=0 oom=0 wrq=0
     29 Acquire: n=7 nul=0 noc=0 ok=1 nbf=0 oom=0 wrq=0
     34 Acquire: n=6 nul=0 noc=0 ok=1 nbf=0 oom=0 wrq=0
     82 Acquire: n=9 nul=0 noc=0 ok=1 nbf=0 oom=0 wrq=0
     93 Acquire: n=5 nul=0 noc=0 ok=1 nbf=0 oom=0 wrq=0

HTH,
Christian.
-- 
BOFH excuse #5:

static from plastic slide rules