Messages in this thread | | | Date | Mon, 22 Oct 2007 15:38:48 -0500 | From | Matt Mackall <> | Subject | Re: [PATCH 09/10] Change table chaining layout |
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On Mon, Oct 22, 2007 at 09:16:17PM +0100, Alan Cox 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.
Also, the current version of SLOB will return objects aligned at 2 bytes if the architecture allows it.
> 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...)
I'm guessing the extra entry makes slab-like allocators unhappy.
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