Re: [PATCH 5/5] slub: Only IPI CPUs that have per cpu obj to flush

[Pekka Enberg <penberg@cs.helsinki.fi>]

On Mon, Sep 26, 2011 at 11:35 AM, Gilad Ben-Yossef <gilad@benyossef.com> wrote:
>> Right, having to do that for_each_oneline_cpu() loop only to then IPI
>> them can cause a massive cacheline bounce fest.. Ideally you'd want to
>> keep a cpumask per kmem_cache, although I bet the memory overhead of
>> that isn't attractive.
>>
>> Also, what Pekka says, having that alloc here isn't good either.
>
> Yes, the alloc in the flush_all path definitively needs to go. I
> wonder if just to resolve that allocating the mask per cpu and not in
> kmem_cache itself is not better - after all, all we need is a single
> mask per cpu when we wish to do a flush_all and no per cache. The
> memory overhead of that is slightly better. This doesn't cover the
> cahce bounce issue.

I'm fine with whatever works for you as long as you don't add a
kmalloc() call in flush_all().

                        Pekka

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