On Mon, Jul 09, 2007 at 05:59:47PM -0700, Christoph Lameter wrote: > On Tue, 10 Jul 2007, Nick Piggin wrote: > > > > Hmmm.... I did not notice that yet but then I have not done much work > > > there. > > > > Notice what? > > The bad code for the buffer heads. Oh. Well my first mail in this thrad listed some of the problems with them. > > > > - A real "nobh" mode. nobh was created I think mainly to avoid problems > > > > with buffer_head memory consumption, especially on lowmem machines. It > > > > is basically a hack (sorry), which requires special code in filesystems, > > > > and duplication of quite a bit of tricky buffer layer code (and bugs). > > > > It also doesn't work so well for buffers with non-trivial private data > > > > (like most journalling ones). fsblock implements this with basically a > > > > few lines of code, and it shold work in situations like ext3. > > > > > > Hmmm.... That means simply page struct are not working... > > > > I don't understand you. jbd needs to attach private data to each bh, and > > that can stay around for longer than the life of the page in the pagecache. > > Right. So just using page struct alone wont work for the filesystems. > > > There are no changes to the filesystem API for large pages (although I > > am adding a couple of helpers to do page based bitmap ops). And I don't > > want to rely on contiguous memory. Why do you think handling of large > > pages (presumably you mean larger than page sized blocks) is strange? > > We already have a way to handle large pages: Compound pages. Yes but I don't want to use large pages and I am not going to use them (at least, they won't be mandatory). > > Conglomerating the constituent pages via the pagecache radix-tree seems > > logical to me. > > Meaning overhead to handle each page still exists? This scheme cannot > handle large contiguous blocks as a single entity? Of course some things have to be done per-page if the pages are not contiguous. I actually haven't seen that to be a problem or have much reason to think it will suddenly become a problem (although I do like Andrea's config page sizes approach for really big systems that cannot change their HW page size). - 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
