Messages in this thread | | | Date | Mon, 22 Oct 2007 23:16:46 +0200 | From | Benny Halevy <> | Subject | Re: [PATCH 09/10] Change table chaining layout |
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On Oct. 22, 2007, 22:16 +0200, Alan Cox <alan@lxorguk.ukuu.org.uk> wrote: > On Mon, 22 Oct 2007 12:49:40 -0700 (PDT) > Linus Torvalds <torvalds@linux-foundation.org> wrote: > >> >> On Mon, 22 Oct 2007, Geert Uytterhoeven wrote: >>> Better safe than sorry... >>> >>> Is it possible that a chain entry pointer has bit 1 set on architectures >>> (e.g. m68k) where the natural alignment of 32-bit quantities is _2_ bytes, >>> not 4? >> Better make sure that such alignment never happens... But no, I don't >> think it will, since these things would generally always have to be >> allocated with an allocator, and the *allocator* won't return 2-byte >> aligned data structures. > > No - but a structure which has other objects in it before the object > being written out may well be 2 byte aligned on M68K and some of the > other externally 16bit platforms - ditto local dynamic objects. > > Why can't we just make the list one item longer than the entry count and > stick a NULL on the end of it like normal people ? Then you need one bit > which ought to be safe for everyone (and if the bit is a macro any CPU > warped enough to have byte alignment is surely going to have top bits > spare...)
Alternatively, I proposed to check for end of list in sg_next by calling it with the next iterator value and number of list elements. We tried that patch here and it seems like a reasonable alternative. If folks are interested, I can send the full patch for review.
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