Re: [RFC][PATCH 0/7] re-shrink 'struct page' when SLUB is on.

[Christoph Lameter]

On Mon, 16 Dec 2013, Dave Hansen wrote:

> I'll do some testing and see if I can coax out any delta from the
> optimization myself.  Christoph went to a lot of trouble to put this
> together, so I assumed that he had a really good reason, although the
> changelogs don't really mention any.

The cmpxchg on the struct page avoids disabling interrupts etc and
therefore simplifies the code significantly.

> I honestly can't imagine that a cmpxchg16 is going to be *THAT* much
> cheaper than a per-page spinlock.  The contended case of the cmpxchg is
> way more expensive than spinlock contention for sure.

Make sure slub does not set __CMPXCHG_DOUBLE in the kmem_cache flags
and it will fall back to spinlocks if you want to do a comparison. Most
non x86 arches will use that fallback code.


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