On Fri, Jan 10, 2020 at 4:18 PM Daniel P. Berrangé <berra...@redhat.com> wrote: > > On Fri, Jan 10, 2020 at 04:13:08PM +0100, Miklos Szeredi wrote: > > On Fri, Jan 10, 2020 at 4:04 PM Dr. David Alan Gilbert > > <dgilb...@redhat.com> wrote: > > > > > > * Daniel P. Berrangé (berra...@redhat.com) wrote: > > > > On Thu, Dec 12, 2019 at 04:38:28PM +0000, Dr. David Alan Gilbert (git) > > > > wrote: > > > > > From: Miklos Szeredi <mszer...@redhat.com> > > > > > > > > > > > > > What is readdirplus and what do we need a command line option to > > > > control it ? What's the user benefit of changing the setting ? > > > > > > cc'ing Miklos who understands this better than me. > > > > > > My understanding is that readdirplus is a heuristic inherited from NFS > > > where when you iterate over the directory you also pick up stat() data > > > for each entry in the directory. You then cache that stat data > > > somewhere. > > > The Plus-ness is that a lot of directory operations involve you stating > > > each entry (e.g. to figure out if you can access it etc) so rolling it > > > into one op avoids the separate stat. The unplus-ness is that it's an > > > overhead and I think changes some of the caching behaviour. > > > > Yeah, so either may give better performance and it's hard to pick a > > clear winner. NFS also has an option to control this. > > IIUC from the man page, the NFS option for controlling this is a client > side mount option. This makes sense as only the client really has knowledge > of whether its workload will benefit. > > With this in mind, should the readdirplus control for virtio-fs also be a > guest mount option instead of a host virtiofsd CLI option ? The guest admin > seems best placed to know whether their workload will benefit or not.
Definitely. In fact other options, e.g. ones that control caching, should probably also be client side (cache=XXX, writeback, timeout=XXX, etc). This needs an extension of the INIT message, so options can be passed to the server. Added this to our TODO list. Thanks, Miklos
