On Saturday 16 June 2012, Arnd Bergmann wrote: > On Friday 15 June 2012, Andreas Dilger wrote: > > > Oh, that's cool. And I don't think that's hard to do. We could just > > > keep a flag in the in-core inode indicating whether it is in "large > > > unit" mode. If it is in large unit mode, we can make the fs writeback > > > function make sure that we adhere to the restrictions of the large > > > unit mode, and if at any point we need to do something that might > > > violate the constraints, the file system would simply close the > > > context. > > > > This is very similar to what was implemented in mballoc preallocation. > > Large files will get their own preallocation context, while small files > > would share a context (i.e. an 8MB extent) and be packed densely into > > this extent to avoid seeking. It wouldn't be unreasonable to just give > > each mballoc context a different eMMC context. > > My understanding is that once we do that, we have already won much more > than we can by using contexts, because we get perfect write patterns. > The only thing that contexts would still buy us is that the device has > more freedom to cache things separately in each context if we write > with less than superpage alignment. Sorry, I replied in the wrong order and had not actually read what Ted said about actually being able to use the large-unit contexts. If we use large-unit contexts in write-only mode, that would indeed be a way for the device to get significantly better than if we just do the alignment. Arnd -- 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
