On Wed, Nov 07, 2007 at 09:02:05AM -0800, Zach Brown wrote: > Badari Pulavarty wrote: > > On Tue, 2007-11-06 at 17:43 -0800, Zach Brown wrote: > >> At the FS meeting at LCE there was some talk of doing O_DIRECT writes from the > >> kernel with pages instead of with iovecs. T > > > > Why ? Whats the use case ? > > Well, I think there's a few: > > There are existing callers which hold a kmap() across ->write, which > isn't great. ecryptfs() does this. That's mentioned in the patch > series. Arguably loopback should be using this instead of copying some > fs paths and trying to call aop methods directly. > > I seem to remember Christoph and David having stories of knfsd folks in > SGI wanting to do O_DIRECT writes from knfsd? (If not, *I* kind of want > to, after rolling some patches to align net rx descriptors :)). The main reason is to remove the serialised writer problem when multiple clients are writing to the one file. With XFS and direct I/O, we can have multiple concurrent writers to the one file and have it scale rather than be limited to what a single cpu holding the i_mutex can do.... > Lustre shows us that there is a point at which you can't saturate your > network and storage if your cpu is copying all the data. Buy more CPUs ;) Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group - 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
