Messages in this thread | | | Date | Thu, 1 Feb 2001 18:02:37 +0100 | From | Christoph Hellwig <> | Subject | Re: [Kiobuf-io-devel] RFC: Kernel mechanism: Compound event wait /notify + callback chains |
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On Thu, Feb 01, 2001 at 04:49:58PM +0000, Stephen C. Tweedie wrote: > > Enquiring minds would like to know if you are working towards this > > revamp of the kiobuf structure at the moment, you have been very quiet > > recently. > > I'm in the middle of some parts of it, and am actively soliciting > feedback on what cleanups are required.
The real issue is that Linus dislikes the current kiobuf scheme. I do not like everything he proposes, but lots of things makes sense.
> I've been merging all of the 2.2 fixes into a 2.4 kiobuf tree, and > have started doing some of the cleanups needed --- removing the > embedded page vector, and adding support for lightweight stacking of > kiobufs for completion callback chains.
Ok, great.
> However, filesystem IO is almost *always* page aligned: O_DIRECT IO > comes from VM pages, and internal filesystem IO comes from page cache > pages. Buffer cache IOs are the only exception, and kiobufs only fail > for such IOs once you have multiple buffer_heads being merged into > single requests. > > So, what are the benefits in the disk IO stack of adding length/offset > pairs to each page of the kiobuf?
I don't see any real advantage for disk IO. The real advantage is that we can have a generic structure that is also usefull in e.g. networking and can lead to a unified IO buffering scheme (a little like IO-Lite).
Christoph
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