Re: [BUG] fscache writing but not reading

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]


On Tue, 16 May 2023 at 20:28, David Wysochanski <dwysocha@xxxxxxxxxx> wrote:
> On Tue, May 16, 2023 at 11:42 AM Chris Chilvers <chilversc@xxxxxxxxx> 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.
> >
> Thanks for the report.
> If you reboot do you see reads from the cache?

On the first read after a reboot it uses the cache, but subsequent
reads do not use the cache.

> You can check if the cache is being read from by looking in
> /proc/fs/fscache/stats
> at the "IO" line:
> # grep IO /proc/fs/fscache/stats
> IO     : rd=80030 wr=0

Running the tests 4 times (twice before reboot, and twice after) give
the following metrics:
FS-Cache I/O (delta)
Run       rd        wr
 1         0    39,250
 2       130    38,894
 3    39,000         0
 4        72    38,991

> Can you share:
> 1. NFS server you're using (is it localhost or something else)
> 2. NFS version

The NFS server and client are separate VMs on the same network.
Server NFS version: Ubuntu 22.04 jammy, kernel 5.15.0-1021-gcp
Client NFS version: Ubuntu 22.04 jammy, kernel 6.4.0-060400rc1-generic
Client nfs-utils: 2.6.3-rc6
Client cachefilesd: 0.10.10-0.2ubuntu1

> In addition to checking the above for the reads from the cache, you can also
> see whether NFS reads are going over the wire pretty easily with a similar
> technique.
> Copy /proc/self/mounstats to a file before your test, then make a second copy
> after the test, then run mountstats as follows:
> mountstats -S /tmp/mountstats.1 -f /tmp/mountstats.2

app read    = applications read bytes via read(2)
client read = client read bytes via NFS READ

Run           app read        client read
 1     322,122,547,200    322,122,547,200
 2     322,122,547,200    321,048,805,376
 3     322,122,547,200                  0
 4     322,122,547,200    321,593,053,184

I've put the full data in a GitHub gist, along with a graph collected
from a metrics agent:

Linux-cachefs mailing list

[Index of Archives]     [LARTC]     [Bugtraq]     [Yosemite Forum]
  Powered by Linux