Hi,
On 10/22/2015 02:54 AM, Gregory Farnum wrote:
On Sun, Oct 18, 2015 at 8:27 PM, Yan, Zheng <ukernel@xxxxxxxxx> wrote:
On Sat, Oct 17, 2015 at 1:42 AM, Burkhard Linke
<Burkhard.Linke@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
Hi,
I've noticed that CephFS (both ceph-fuse and kernel client in version 4.2.3)
remove files from page cache as soon as they are not in use by a process
anymore.
Is this intended behaviour? We use CephFS as a replacement for NFS in our
HPC cluster. It should serve large files which are read by multiple jobs on
multiple hosts, so keeping them in the page cache over the duration of
several job invocations is crucial.
Yes. MDS needs resource to track the cached data. We don't want MDS
use too much resource.
So if I'm reading things right, the code to drop the page cache for
ceph-fuse was added in https://github.com/ceph/ceph/pull/1594
(specifically 82015e409d09701a7048848f1d4379e51dd00892). I don't think
it's actually needed for the cap trimming stuff or to prevent MDS
cache pressure and it's actually not clear to me why it was added here
anyway. But you do say the PR as a whole fixed a lot of bugs. Do you
know if the page cache clearing was for any bugs in particular, Zheng?
In general I think proactively clearing the page cache is something we
really only want to do as part of our consistency and cap handling
story, and file closes don't really play into that. I've pushed a
TOTALLY UNTESTED (NOT EVEN COMPILED) branch client-pagecache-norevoke
based on master to the gitbuilders. If it does succeed in building you
should be able to download it and you can use it for testing, or
cherry-pick the top commit out of git and build your own packages.
Then set the (new to this branch) client_preserve_pagecache config
option to true (default: false) and it should avoid flushing the page
cache.
Thanks a lot for having a closer look at this. I'm currently preparing
the deployment of 0.94.4 (or 0.94.5 due to rbd bug), and need to add
some patches to ceph-fuse for correct permission handling. I'll
cherry-pick the changes of that branch and test the package.
Regards,
Burkhard
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