On Tue, Jun 26, 2007 at 07:23:09PM +1000, David Chinner wrote: > On Tue, Jun 26, 2007 at 01:55:11PM +1000, Nick Piggin wrote: [ ... fsblocks vs extent range mapping ] > iomaps can double as range locks simply because iomaps are > expressions of ranges within the file. Seeing as you can only > access a given range exclusively to modify it, inserting an empty > mapping into the tree as a range lock gives an effective method of > allowing safe parallel reads, writes and allocation into the file. > > The fsblocks and the vm page cache interface cannot be used to > facilitate this because a radix tree is the wrong type of tree to > store this information in. A sparse, range based tree (e.g. btree) > is the right way to do this and it matches very well with > a range based API. I'm really not against the extent based page cache idea, but I kind of assumed it would be too big a change for this kind of generic setup. At any rate, if we'd like to do it, it may be best to ditch the idea of "attach mapping information to a page", and switch to "lookup mapping information and range locking for a page". A btree could be used to hold the range mapping and locking, but it could just as easily be a radix tree where you do a gang lookup for the end of the range (the same way my placeholder patch did). It'll still find intersecting range locks but is much faster for random insertion/deletion than the btrees. -chris - 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
