2012/5/16 Matthew Wilcox <willy@xxxxxxxxxxxxxxx>: > On Tue, May 15, 2012 at 10:46:39AM -0700, Greg KH wrote: >> On Tue, May 15, 2012 at 09:34:51AM -0400, Matthew Wilcox wrote: >> > What we'd really like is for people to think about how they might use >> > fast NVM inside the kernel. There's likely to be a lot of it (at least in >> > servers); all the technologies are promising cheaper per-bit prices than >> > DRAM, so it's likely to be sold in larger capacities than DRAM is today. >> > >> > Caching is one obvious use (be it FS-Cache, Bcache, Flashcache or >> > something else), but I bet there are more radical things we can do >> > with it. What if we stored the inode cache in it? Would booting with >> > a hot inode cache improve boot times? How about storing the tree of >> > 'struct devices' in it so we don't have to rescan the busses at startup? >> >> Rescanning the busses at startup are required anyway, as devices can be >> added and removed when the power is off, and I would be amazed if that >> is actually taking any measurable time. Do you have any numbers for >> this for different busses? > > Hi Greg, > > I wasn't particularly serious about this example ... I did once time > the scan of a PCIe bus and it took a noticable number of milliseconds > (which is why we now only scan the first device for the downstream "bus" > of root ports and downstream ports). > > I'm just trying to stimulate a bit of discussion of possible usages for > persistent memory. > >> What about pramfs for the nvram? I have a recent copy of the patches, >> and I think they are clean enough for acceptance, there was no >> complaints the last time it was suggested. Can you use that for this >> type of hardware? > > pramfs is definitely one filesystem that's under investigation. I know > there will be types of NVM for which it won't be suitable, so rather For example? > than people calling pramfs-specific functions, the notion is to get a > core API in the VFS that can call into the various different filesystems > that can handle the vagaries of different types of NVM. > The idea could be good but I have doubt about it. Any fs is designed for a specific environment, to provide VFS api to manage NVM is not enough. I mean, a fs designed to reduce the seek time on hd, it adds not needed complexity for this kind of environment. Maybe the goal could be only for a "specific" support, for the journal for example. Marco -- 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
