On 01/16/2014 08:44 AM, Christoph Lameter wrote:
> On Tue, 14 Jan 2014, Dave Hansen wrote:
>
>> On 01/14/2014 12:07 PM, Christoph Lameter wrote:
>>> One easy way to shrink struct page is to simply remove the feature. The
>>> patchset looked a bit complicated and does many other things.
>>
>> Sure. There's a clear path if you only care about 'struct page' size,
>> or if you only care about making the slub fast path as fast as possible.
>> We've got three variables, though:
>>
>> 1. slub fast path speed
>
> The fast path does use this_cpu_cmpxchg_double which is something
> different from a cmpxchg_double and its not used on struct page.
Yeah, I'm confusing the two. I might as well say: "slub speed when
touching 'struct page'"
>> Arranged in three basic choices:
>>
>> 1. Big 'struct page', fast, medium complexity code
>> 2. Small 'struct page', slow, lowest complexity
>
> The numbers that I see seem to indicate that a big struct page means slow.
This was a really tight loop where the caches are really hot, but it did
show the large 'struct page' winning:
http://sr71.net/~dave/intel/slub/slub-perf-20140109.png
As I said in the earlier description, the paravirt code doing interrupt
disabling was what really hurt the two spinlock cases.
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