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From:   David Wysochanski <dwysocha@redhat.com>
Date:   Tue, 23 May 2023 10:15:48 -0400
Message-ID: <CALF+zOmbORezpTam09CAvZmPu2KzwR==KNpA32xe90eVkSDK0g@mail.gmail.com>
Subject: Re: [Linux-cachefs] [BUG] fscache writing but not reading
To:     Chris Chilvers <chilversc@gmail.com>
Cc:     David Howells <dhowells@redhat.com>,
        Benjamin Maynard <benmaynard@google.com>,
        linux-nfs@vger.kernel.org, linux-cachefs@redhat.com,
        brennandoyle@google.com
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On Tue, May 23, 2023 at 7:18=E2=80=AFAM Chris Chilvers <chilversc@gmail.com=
> wrote:
>
> 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 i=
n 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-do=
c.tar.bz2
> >         cat /proc/fs/fscache/stats
>
> FS-Cache statistics
> Cookies: n=3D13 v=3D7 vcol=3D0 voom=3D0
> Acquire: n=3D13 ok=3D13 oom=3D0
> LRU    : n=3D1 exp=3D0 rmv=3D0 drp=3D0 at=3D2833
> Invals : n=3D0
> Updates: n=3D0 rsz=3D0 rsn=3D0
> Relinqs: n=3D0 rtr=3D0 drop=3D0
> NoSpace: nwr=3D0 ncr=3D0 cull=3D0
> IO     : rd=3D0 wr=3D18
> RdHelp : RA=3D18 RP=3D0 WB=3D0 WBZ=3D0 rr=3D0 sr=3D0
> RdHelp : ZR=3D1 sh=3D0 sk=3D0
> RdHelp : DL=3D18 ds=3D18 df=3D0 di=3D0
> RdHelp : RD=3D0 rs=3D0 rf=3D0
> RdHelp : WR=3D18 ws=3D18 wf=3D0
>
> 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-do=
c.tar.bz2
> >         cat /proc/fs/fscache/stats
>
> FS-Cache statistics
> Cookies: n=3D13 v=3D7 vcol=3D0 voom=3D0
> Acquire: n=3D26 ok=3D26 oom=3D0
> LRU    : n=3D1 exp=3D1 rmv=3D0 drp=3D0 at=3D467
> Invals : n=3D0
> Updates: n=3D0 rsz=3D0 rsn=3D0
> Relinqs: n=3D13 rtr=3D0 drop=3D13
> NoSpace: nwr=3D0 ncr=3D0 cull=3D0
> IO     : rd=3D18 wr=3D18
> RdHelp : RA=3D36 RP=3D0 WB=3D0 WBZ=3D0 rr=3D0 sr=3D0
> RdHelp : ZR=3D1 sh=3D0 sk=3D0
> RdHelp : DL=3D18 ds=3D18 df=3D0 di=3D0
> RdHelp : RD=3D18 rs=3D18 rf=3D0
> RdHelp : WR=3D18 ws=3D18 wf=3D0
>
> Looks like the cache is working fine with AFS. The second md5sum
> seemed a lot quicker than the first.
>
> --
> Linux-cachefs mailing list
> Linux-cachefs@redhat.com
> https://listman.redhat.com/mailman/listinfo/linux-cachefs
>

I don't think this test demonstrates the failure Chris is seeing, or
correct me if I'm wrong Chris.

Chris, does this same test fail for you with NFS on 6.4-rc1?  The same
test passes for me with NFSv3.
1st time through: writes to the cache seen, no reads: IO     : rd=3D0 wr=3D=
16
2nd time through: reads from the cache seen, no writes: IO     : rd=3D16 wr=
=3D16


# mount -o vers=3D3,fsc 127.0.0.1:/export/ /mnt/nfs
# cat /proc/fs/fscache/stats
FS-Cache statistics
Cookies: n=3D0 v=3D1 vcol=3D0 voom=3D0
Acquire: n=3D0 ok=3D0 oom=3D0
LRU    : n=3D0 exp=3D0 rmv=3D0 drp=3D0 at=3D0
Invals : n=3D0
Updates: n=3D0 rsz=3D0 rsn=3D0
Relinqs: n=3D0 rtr=3D0 drop=3D0
NoSpace: nwr=3D0 ncr=3D0 cull=3D0
IO     : rd=3D0 wr=3D0
RdHelp : RA=3D0 RP=3D0 WB=3D0 WBZ=3D0 rr=3D0 sr=3D0
RdHelp : ZR=3D0 sh=3D0 sk=3D0
RdHelp : DL=3D0 ds=3D0 df=3D0 di=3D0
RdHelp : RD=3D0 rs=3D0 rf=3D0
RdHelp : WR=3D0 ws=3D0 wf=3D0
# md5sum /mnt/nfs/openafs-1.9.1-doc.tar.bz2
ca25530ec01afc3b71bc081bc93b87cf  /mnt/nfs/openafs-1.9.1-doc.tar.bz2
# cat /proc/fs/fscache/stats
FS-Cache statistics
Cookies: n=3D1 v=3D1 vcol=3D0 voom=3D0
Acquire: n=3D1 ok=3D1 oom=3D0
LRU    : n=3D1 exp=3D0 rmv=3D0 drp=3D0 at=3D6444
Invals : n=3D0
Updates: n=3D1 rsz=3D0 rsn=3D0
Relinqs: n=3D0 rtr=3D0 drop=3D0
NoSpace: nwr=3D0 ncr=3D0 cull=3D0
IO     : rd=3D0 wr=3D16
RdHelp : RA=3D16 RP=3D0 WB=3D0 WBZ=3D0 rr=3D0 sr=3D0
RdHelp : ZR=3D1 sh=3D0 sk=3D0
RdHelp : DL=3D16 ds=3D16 df=3D0 di=3D0
RdHelp : RD=3D0 rs=3D0 rf=3D0
RdHelp : WR=3D16 ws=3D16 wf=3D0
# umount /mnt/nfs
# mount -o vers=3D3,fsc 127.0.0.1:/export/ /mnt/nfs
# md5sum /mnt/nfs/openafs-1.9.1-doc.tar.bz2
ca25530ec01afc3b71bc081bc93b87cf  /mnt/nfs/openafs-1.9.1-doc.tar.bz2
# cat /proc/fs/fscache/stats
FS-Cache statistics
Cookies: n=3D1 v=3D1 vcol=3D0 voom=3D0
Acquire: n=3D2 ok=3D2 oom=3D0
LRU    : n=3D1 exp=3D1 rmv=3D0 drp=3D0 at=3D6710
Invals : n=3D0
Updates: n=3D2 rsz=3D0 rsn=3D0
Relinqs: n=3D1 rtr=3D0 drop=3D1
NoSpace: nwr=3D0 ncr=3D0 cull=3D0
IO     : rd=3D16 wr=3D16
RdHelp : RA=3D32 RP=3D0 WB=3D0 WBZ=3D0 rr=3D0 sr=3D0
RdHelp : ZR=3D1 sh=3D0 sk=3D0
RdHelp : DL=3D16 ds=3D16 df=3D0 di=3D0
RdHelp : RD=3D16 rs=3D16 rf=3D0
RdHelp : WR=3D16 ws=3D16 wf=3D0
# uname -r
6.4.0-rc1