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Subject: Re: [patch] SLQB slab allocator (try 2)
From: Pekka Enberg <penberg@cs.helsinki.fi>
To: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Christoph Lameter <cl@linux-foundation.org>,
       Johannes Weiner <hannes@cmpxchg.org>, Mel Gorman <mel@csn.ul.ie>,
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       "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
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Date: Thu, 19 Feb 2009 11:16:07 +0200
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On Wed, 2009-02-18 at 09:48 +0900, KOSAKI Motohiro wrote:
> > > In addition, if pekka patch (SLAB_LIMIT = 8K) run on ia64, 16K allocation 
> > > always fallback to page allocator and using 64K (4 times memory consumption!).
> > 
> > Yes, correct, but SLUB does that already by passing all allocations over
> > 4K to the page allocator.
> 
> hmhm
> OK. my mail was pointless.
> 
> but why? In my understanding, slab framework mainly exist for efficient
> sub-page allocation.
> the fallbacking of 4K allocation in 64K page-sized architecture seems
> inefficient.

I don't think any of the slab allocators are known for memory
efficiency. That said, the original patch description sums up the
rationale for page allocator pass-through:

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=aadb4bc4a1f9108c1d0fbd121827c936c2ed4217

Interesting enough, there seems to be some performance gain from it as
well as seen by Mel Gorman's recent slab allocator benchmarks.

			Pekka