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From:   Chris Chilvers <chilversc@gmail.com>
Date:   Tue, 23 May 2023 12:18:08 +0100
Message-ID: <CAAmbk-ffz-6LqkEo+XavgiuefZK7BOHC7648ZhSs0BN88N=M4A@mail.gmail.com>
Subject: Re: [Linux-cachefs] [BUG] fscache writing but not reading
To:     David Howells <dhowells@redhat.com>
Cc:     linux-nfs@vger.kernel.org, linux-cachefs@redhat.com,
        brennandoyle@google.com, Benjamin Maynard <benmaynard@google.com>
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On Fri, 19 May 2023 at 10:40, David Howells <dhowells@redhat.com> wrote:
>
> Chris Chilvers <chilversc@gmail.com> wrote:
>
> > While testing the fscache performance fixes [1] that were merged into 6.4-rc1
> > it appears that the caching no longer works. The client will write to the cache
> > but never reads.
>
> Can you try reading from afs?  You would need to enable CONFIG_AFS_FS in your
> kernel if it's not already set.
>
> Install kafs-client and do:
>
>         systemctl enable afs.mount
>         md5sum /afs/openafs.org/software/openafs/1.9.1/openafs-1.9.1-doc.tar.bz2
>         cat /proc/fs/fscache/stats

FS-Cache statistics
Cookies: n=13 v=7 vcol=0 voom=0
Acquire: n=13 ok=13 oom=0
LRU    : n=1 exp=0 rmv=0 drp=0 at=2833
Invals : n=0
Updates: n=0 rsz=0 rsn=0
Relinqs: n=0 rtr=0 drop=0
NoSpace: nwr=0 ncr=0 cull=0
IO     : rd=0 wr=18
RdHelp : RA=18 RP=0 WB=0 WBZ=0 rr=0 sr=0
RdHelp : ZR=1 sh=0 sk=0
RdHelp : DL=18 ds=18 df=0 di=0
RdHelp : RD=0 rs=0 rf=0
RdHelp : WR=18 ws=18 wf=0

This was on an instance that was only just created, so the cache was
initially unused (all the counters were 0).

>         umount /afs/openafs.org
>         md5sum /afs/openafs.org/software/openafs/1.9.1/openafs-1.9.1-doc.tar.bz2
>         cat /proc/fs/fscache/stats

FS-Cache statistics
Cookies: n=13 v=7 vcol=0 voom=0
Acquire: n=26 ok=26 oom=0
LRU    : n=1 exp=1 rmv=0 drp=0 at=467
Invals : n=0
Updates: n=0 rsz=0 rsn=0
Relinqs: n=13 rtr=0 drop=13
NoSpace: nwr=0 ncr=0 cull=0
IO     : rd=18 wr=18
RdHelp : RA=36 RP=0 WB=0 WBZ=0 rr=0 sr=0
RdHelp : ZR=1 sh=0 sk=0
RdHelp : DL=18 ds=18 df=0 di=0
RdHelp : RD=18 rs=18 rf=0
RdHelp : WR=18 ws=18 wf=0

Looks like the cache is working fine with AFS. The second md5sum
seemed a lot quicker than the first.