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    SubjectRe: [PATCH 09/10] Change table chaining layout
    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.

    --
    Mathematics is the supreme nostalgia of our time.
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