Messages in this thread | | | Date | Tue, 17 Dec 2013 15:17:37 +0000 | From | Christoph Lameter <> | Subject | Re: [RFC][PATCH 0/7] re-shrink 'struct page' when SLUB is on. |
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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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