Re: [rfc][patch 3/3] use SLAB_ALIGN_SMP

[Pekka Enberg]

Hi,

On Mon, Mar 3, 2008 at 3:46 PM, Nick Piggin <npiggin@xxxxxxx> wrote:
>  > Maybe we need to use three flags to separate the meanings ?
>  >
>  > SLAB_HINT_SMP_ALIGN
>  > SLAB_HINT_HWCACHE_ALIGN
>  > SLAB_HWCACHE_ALIGN /* strong requirement that two objects dont share a
>  > cache line */
>
>  Possibly, but I'm beginning to prefer that strong requirements should
>  request the explicit alignment (they can even use cache_line_size() after
>  Pekka's patch to make it generic). I don't like how the name implies
>  that you get a guarantee, however I guess in practice people are using it
>  more as a hint (or because they vaguely hope it makes their code run
>  faster :))

At least historically SLAB_HWCACHE_ALIGN has been just a hint,
although slab tries very hard to satisfy it (see the comments in
mm/slab.c). Why do we need stronger guarantees than that, btw?
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