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Message-Id: <20071022.170741.41638232.davem@davemloft.net> Date: Mon, 22 Oct 2007 17:07:41 -0700 (PDT) From: David Miller <davem@...emloft.net> To: torvalds@...ux-foundation.org Cc: alan@...rguk.ukuu.org.uk, geert@...ux-m68k.org, jens.axboe@...cle.com, linux-kernel@...r.kernel.org, mingo@...e.hu, linux-m68k@...r.kernel.org Subject: Re: [PATCH 09/10] Change table chaining layout From: Linus Torvalds <torvalds@...ux-foundation.org> Date: Mon, 22 Oct 2007 14:47:38 -0700 (PDT) > On Mon, 22 Oct 2007, Alan Cox wrote: > > > Still doesn't answer the rather more important question - why not just > > stick a NULL on the end instead of all the nutty hacks ? > > You still do need one bit for the discontiguous case, so it's not like you > can avoid the hacks anyway (unless you just blow up the structure > entirely) and make it a separate member). So once you have that > bit+pointer, using a separate NULL entry isn't exactly prettier. > > Especially as we actally want to see the difference between > "end-of-allocation" and "not yet filled in", so you shouldn't use NULL > anyway, you should probably use something like "all-ones". Indeed that's the crux of the matter, we need to express a trinary state "end of scatterlist, next entry is linear, next entry is indirect" plus a pointer for the indirect case. Generally, Jens was doing a good job cooking up the patch that implemented this fully and I took care of making sure tricky ports like sparc64 built cleanly etc. He went away for a few days, but when he gets back we should seriously work on integrating his work. I fully recognize Alan's m68k on-stack alignment concern. The on-stack cases are troublesome in other ways as well, and I think therefore the way to move forward is to convert those to some kind of dynamic scheme. Usually such code is working in a locked context on some object (crypto instance, for example) and thus the scatterlist chunk can be embedded into that object for ensured alignment. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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