On Sat, 2007-10-27 at 23:30 +0200, Peter Zijlstra wrote: > On Sat, 2007-10-27 at 16:02 -0500, Steve French wrote: > > On 10/27/07, Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote: > > > Hi, > > > > > > I had me a little look at bdi usage in networked filesystems. > > > > > > NFS, CIFS, (smbfs), AFS, CODA and NCP > > > > > > And of those, NFS is the only one that I could find that creates > > > backing_dev_info structures. The rest seems to fall back to > > > default_backing_dev_info. > > > > > > With my recent per bdi dirty limit patches the bdi has become more > > > important than it has been in the past. While falling back to the > > > default_backing_dev_info isn't wrong per-se, it isn't right either. > > > > > > Could I implore the various maintainers to look into this issue for > > > their respective filesystem. I'll try and come up with some patches to > > > address this, but feel free to beat me to it. > > > > I would like to understand more about your patches to see what bdi > > values makes sense for CIFS and how to report possible congestion back > > to the page manager. > > So, what my recent patches do is carve up the total writeback cache > size, or dirty page limit as we call it, proportionally to a BDIs > writeout speed. So a fast device gets more than a slow device, but will > not starve it. > > However, for this to work, each device, or remote backing store in the > case of networked filesystems, need to have a BDI. > > > I had been thinking about setting bdi->ra_pages > > so that we do more sensible readahead and writebehind - better > > matching what is possible over the network and what the server > > prefers. > > Well, you'd first have to create backing_dev_info instances before > setting that value :-) > > > SMB/CIFS Servers typically allow a maximum of 50 requests > > in parallel at one time from one client (although this is adjustable > > for some). > > That seems like a perfect point to set congestion. > > So in short, stick a struct backing_dev_info into whatever represents a > client, initialize it using bdi_init(), destroy using bdi_destroy(). Oh, and the most important point, make your fresh I_NEW inodes point to this bdi struct. > Mark it congested once you have 50 (or more) outstanding requests, clear > congestion when you drop below 50. > > and you should be set. > - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
