Re: SLUB

[Christoph Lameter <clameter@sgi.com>]

On Thu, 20 Dec 2007, Mark Seger wrote:

> I did some preliminary prototyping and I guess I'm not sure of the math.  If I
> understand what you're saying, an object has a particular size, but given the
> fact that you may need alignment, the true size is really the slab size, and
> the difference is the overhead.  What I don't understand is how to calculate
> how much memory a particular slab takes up.  If the slabsize is really the

If you want the use in terms of pages allocated from the page allocator 
then you do

slabs << order

If you want to use in actual bytes in allocated objects by the user of 
a slab cache then you can do

objects * obj_size

> this IS close enough?  If so, what's the significance of the number of slabs?

Its the amount of pages that were taken from the page allocator.

> Would I divide the 15997K by the number of slabs to find out how big a single
> slab is?  I would have thought that's what the slab_size is but clearly it
> isn't.

The size of a single slab that contains multiple objects is

PAGE_SIZE << order

> 49 N0=19 N1=30
> 
> which I'm guessing may mean 19 objects are allocated to socket 0 and 30 to
> socket 1?  this is a dual-core, dual-socket system.

Right. There are 49 objects in use. 19 of those are on node 0 and 30 on 
node 0. The Nx values only show up on NUMA systems otherwise this will be 
omitted.


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