On Tue, May 08, 2007 at 07:57:37PM -0700, Christoph Lameter wrote:
> On Wed, 9 May 2007, Nick Piggin wrote:
>
> > > Exactly. That overhead does not exist in SLUB. Thus SLOB is less efficient
> > > than SLUB.
> >
> > What you trade for that is that one page page can only serve one slab.
>
> Right.
>
> > For small systems, I would not be surprised if that was less space
> > efficient, even just looking at kmalloc caches in isolation. Or do you
> > have numbers to support your conclusion?
>
> No I do not have any number beyond the efficiency calculations based on
> whole slabs. We would have to do some experiments to figure out how much
> space is actually wasted through partial slabs.
The expectation would be (PAGE_SIZE + (PAGE_SIZE % size))/2 on average
per cache.
> The situation becomes different with allocation and frees. Then we may
> have lots of partial slabs that we allocate from. But the SLOB approach
> also will have holes to manage. So I do not see how this could be a
> benefit unless you only have a few precious pages and you need to put
> multiple object sizes into it. A 4M system still has 1000 pages.
A 4M system has approximately zero pages free once you've actually got
stuff running in userspace. The marginal utility of each page is very
high.
--
Mathematics is the supreme nostalgia of our time.
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